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A new perspective of storm bite on sandy beaches using Unmanned Aerial Vehicles
Abstract
Aerial imagery collected before and after major storm events is ideal for the assessment of coastal landscape change driven by individual high-magnitude events. Using traditional satellite sensors and manned aerial systems can be challenging due to issues related to cloud cover, mobilization expenses and resolution. Rapid advances in unmanned aerial vehicle (UAV) technology allow for the cost-effective collection of aerial imagery and topography at centimetre resolution suitable for assessing change in coastal ecosystems. In this study we demonstrate the utility of UAV-based photogrammetry to quantify storm-driven sediment dynamics on a sandy beach on the open-coast shoreline of Victoria, Aus-tralia. UAV-based aerial photography was collected before and after a major storm event. High-resolution (< 5 cm) aerial imagery and digital surface models were acquired and change-detection techniques were applied to quantify changes in the beachface. An average beach erosion of 12.24 m 3 /m with a maximum of 28.05 m 3 /m was observed, and the volume of sand cut from the beachface and retreat of the foredune are clearly illustrated. Following the storm event, erosion was estimated at 7259.94 ± 503.69 m 3 along 550 m of beach. By combining the aerial imagery and derived topographic datasets we demonstrate the advantage of UAV-based photogrammetry techniques for rapid high-resolution data collection in semi-remote locations. Its utility in setting unlimited virtual vantage points is also illustrated and the valuable perspective it provides for tracking landscape change discussed.
... The UAV studies mainly consist of taking images using a red-green-blue (RGB) camera mounted onto a suitable UAV platform and processing those images using a SfM workflow within a suitable software to derive DSMs/DEMs/orthomosaics [67,[86][87][88][89][90][91][92][93][94][95][96]. Although most authors used only a single type of UAV for conducting the studies [86,87,[89][90][91][92][93][94][95][96], others used different types of UAVs [67] and different models of the same UAV [88] to discern any differences in the output induced due to different UAV types/models. ...
... The UAV studies mainly consist of taking images using a red-green-blue (RGB) camera mounted onto a suitable UAV platform and processing those images using a SfM workflow within a suitable software to derive DSMs/DEMs/orthomosaics [67,[86][87][88][89][90][91][92][93][94][95][96]. Although most authors used only a single type of UAV for conducting the studies [86,87,[89][90][91][92][93][94][95][96], others used different types of UAVs [67] and different models of the same UAV [88] to discern any differences in the output induced due to different UAV types/models. While [67] found that the markedly lower cost quadcopter outperformed the more expensive fixed-wing UAV with DSM accuracy values comparable to a reference lidar DEM and the ground truth data, Ref. [88] found that a more recent version of the same UAV quadcopter fitted with a 20 Mpix camera resulted in a substantially more accurate DSM and that the DSM from the lower-cost version largely met the standards for coastal monitoring. ...
... GCPs are used for georeferencing, and though it is possible that the aerial images are already geolocated by the UAV's autopilot, the utilisation of external GCPs lead to more accurate results (lower standard error) of the DSMs/DEMs/orthomosaics [67,86,93]. Additionally, Ref. [88] also demonstrated a positive correlation between number of GCPs and DSM vertical accuracy. ...
Unequivocal change in the climate system has put coastal regions around the world at increasing risk from climate-related hazards. Monitoring the coast is often difficult and expensive, resulting in sparse monitoring equipment lacking in sufficient temporal and spatial coverage. Thus, low-cost methods to monitor the coast at finer temporal and spatial resolution are imperative for climate resilience along the world’s coasts. Exploiting such low-cost methods for the development of early warning support could be invaluable to coastal settlements. This paper aims to provide the most up-to-date low-cost techniques developed and used in the last decade for monitoring coastal hazards and their forcing agents via systematic review of the peer-reviewed literature in three scientific databases: Scopus, Web of Science and ScienceDirect. A total of 60 papers retrieved from these databases through the preferred reporting items for systematic reviews and meta-analyses (PRISMA) protocol were analysed in detail to yield different categories of low-cost sensors. These sensors span the entire domain for monitoring coastal hazards, as they focus on monitoring coastal zone characteristics (e.g., topography), forcing agents (e.g., water levels), and the hazards themselves (e.g., coastal flooding). It was found from the meta-analysis of the retrieved papers that terrestrial photogrammetry, followed by aerial photogrammetry, was the most widely used technique for monitoring different coastal hazards, mainly coastal erosion and shoreline change. Different monitoring techniques are available to monitor the same hazard/forcing agent, for instance, unmanned aerial vehicles (UAVs), time-lapse cameras, and wireless sensor networks (WSNs) for monitoring coastal morphological changes such as beach erosion, creating opportunities to not only select but also combine different techniques to meet specific monitoring objectives. The sensors considered in this paper are useful for monitoring the most pressing challenges in coastal zones due to the changing climate. Such a review could be extended to encompass more sensors and variables in the future due to the systematic approach of this review. This study is the first to systematically review a wide range of low-cost sensors available for the monitoring of coastal zones in the context of changing climate and is expected to benefit coastal researchers and managers to choose suitable low-cost sensors to meet their desired objectives for the regular monitoring of the coast to increase climate resilience.
... LB was subject to rapid sediment accretion and progradation of over 300m on its western side, and some erosion along its northern shore, following a succession of coastal management decisions which included the construction of the viaduct and the breakwater in the late 1800s (Gill, 1984). More recently, seasonal analysis of four multibeam echosounder surveys conducted by Schimel et al. (2015) revealed that the seafloor of the bay near the breakwater experienced large sediment transfer (mostly erosion) between July and November 2013, whereas Ierodiaconou et al. (2016) calculated a volumetric loss of approximately 7260m 3 (average of 12.2m 3 m À1 ) from the beachface and consequent retreat of the foredune along 550 m of shoreline near the breakwater following a major southwesterly storm event that happened in June 2014. ...
... Volumetric analysis was limited to the DoD pixels displaying an absolute value larger than the limit of detection (LoD), which accounted for areas that experienced little change being removed from the calculations (Ierodiaconou et al., 2016). A LoD was used for each DoD based on the standard deviation of RMSEs reported in Table III, as an estimation of its inherent uncertainty. ...
... The general overlapping of the three cross-section lines in the first 500m of LB (Figure 6d) suggests that the erosion occurred after 1986. This recent erosional pattern in the 500m close to the breakwater was also observed by Ierodiaconou et al. (2016) following a southwesterly storm in 2014, which removed a maximum of 28 m 3 m À1 from the area. The fact that the decadal maximum volumetric cut was about half of that calculated for the storm event can be attributed to the beach nourishment that occurred during the dredging of Warrnambool Harbour in 2001 and 2005, which possibly added an extra 46000m 3 to the shoreline (GHD, 2009), and also to the long time needed for these environments to recover from single events as observed in other sandy beaches (McLean and Shen, 2006;Turner et al., 2016). ...
Historical aerial photographs are an invaluable tool in shoreline mapping and change detection in coastal landscapes. We evaluate the extent to which Structure‐from‐Motion (SfM) photogrammetric methods can be applied to quantify volumetric changes along sandy beaches, using archival imagery. We demonstrate the application of SfM‐derived Digital Surface Models (DSMs) at East Beach and Lady Bay in southwest Victoria, Australia, using photographic datasets taken in 1969, 1977 and 1986, and compared them to Light Detection and Ranging‐derived DSMs acquired at both sites in 2007. The SfM approaches resulted in two entire and two partial suitable DSMs out of six datasets. Good quality DSMs were spatially‐continuous with a good spread of Ground Control Points (GCPs) near the beach at Lady Bay, whereas unsuitable DSMs were mostly restricted by poor distribution and number of GCPs in spatially‐segmented areas of East Beach, due to limited overlapping of images, possible poor quality of GCPs and also the propagation of error in the derived point clouds. A volume of approximately 223,000 ± 72,000 m3 was deposited at Lady Bay between 1969 and 2007, despite minimal erosion observed near the breakwater. The partially suitable dataset of East Beach indicated that beach erosion of at least 39 m3/m occurred immediately to the east of the seawall after 1977. We also discuss the drawbacks and strengths of SfM approaches as benchmark of historical erosion assessments along sandy beaches.
... The potential of UAVs for environmental assessment and monitoring is increasingly being demonstrated, and the impacts of environmental disturbances can be assessed rapidly because of the ease of deployment and portability of UAVs 14,15 . Recent studies show the advantage of using UAVs in forest and crop monitoring 16,17 , monitoring coastal erosion 15,18,19 , and quantification of submerged vegetation in shallow water 20 . ...
... The potential of UAVs for environmental assessment and monitoring is increasingly being demonstrated, and the impacts of environmental disturbances can be assessed rapidly because of the ease of deployment and portability of UAVs 14,15 . Recent studies show the advantage of using UAVs in forest and crop monitoring 16,17 , monitoring coastal erosion 15,18,19 , and quantification of submerged vegetation in shallow water 20 . UAV systems can also use multispectral sensors to assist with identification of species and vegetation health via spectral classifications 21 and can be deployed to perform population censuses of species in remote or difficult to access areas [22][23][24] . ...
... Whilst UAVs have been used to assess broad-scale coastal morphology along beaches and sand dunes 15,19,25 applications to intertidal reef systems to investigate community structure have been limited, though a few studies have considered innovative ways to capture intertidal reefs at a much higher resolution using low altitude remote sensing platforms. For example, a blimp fitted with a multispectral sensor was deployed to map an intertidal reef from an altitude of 80 m to estimate algal biomass using normalised difference vegetation indices (NDVI) and topographic heterogeneity of the reef for scale-dependent analyses of algal-topography relationships 26 . ...
Monitoring of intertidal reefs is traditionally undertaken by on-ground survey methods which have assisted in understanding these complex habitats; however, often only a small spatial footprint of the reef is observed. Recent developments in unmanned aerial vehicles (UAVs) provide new opportunities for monitoring broad scale coastal ecosystems through the ability to capture centimetre resolution imagery and topographic data not possible with conventional approaches. This study compares UAV remote sensing of intertidal reefs to traditional on-ground monitoring surveys, and investigates the role of UAV derived geomorphological variables in explaining observed intertidal algal and invertebrate assemblages. A multirotor UAV was used to capture <1 cm resolution data from intertidal reefs, with on-ground quadrat surveys of intertidal biotic data for comparison. UAV surveys provided reliable estimates of dominant canopy-forming algae, however, understorey species were obscured and often underestimated. UAV derived geomorphic variables showed elevation and distance to seaward reef edge explained 19.7% and 15.9% of the variation in algal and invertebrate assemblage structure respectively. The findings of this study demonstrate benefits of low-cost UAVs for intertidal monitoring through rapid data collection, full coverage census, identification of dominant canopy habitat and generation of geomorphic derivatives for explaining biological variation.
... In parallel, the development and popularization of unmanned aerial vehicles (UAVs) and structure-from-motion (SfM) have fostered new perspectives in coastal monitoring and geomorphology studies (Brunier et al., 2016;Colomina & Molina, 2014;Gonçalves & Henriques, 2015). As a result, studies on contemporary change detection and volumetric analysis have been conducted on beaches worldwide, including Italy (Mancini et al., 2013), Ireland (Guisado-Pintado et al., 2019), French Guiana (Brunier et al., 2016), Australia (Ierodiaconou et al., 2016), Malaysia and the Solomon Islands (Lowe et al., 2019), and the United States (Wernette et al., 2020). ...
... Volumetric analyses were limited to the DoD pixels that had absolute values larger than the limit of detection (LoD), which accounted for areas subject to minimal change being removed from the calculations (Ierodiaconou et al., 2016). An LoD was used for each DoD based on the standard deviation of RMSEs (Table 3) and ...
Technological advances have reinvigorated the aerial photogrammetric technique using both historical and contemporary imagery, and fostered new perspectives in geomorphology studies. On sandy beaches, however, the dynamic processes, the lack of tonal contrast and reduced texture, make the application of photogrammetry extremely more difficult than in most other landscapes. This study quantifies decadal volumetric changes along the beaches of the Great Ocean Road, Australia, using improved Digital Surface Models (DSMs) derived from Structure‐from‐Motion (SfM) photogrammetry applied to historical archives and a contemporary Unmanned Aerial Vehicle survey. Alongside surficial sediment analysis, this approach demonstrates the potential to relate present‐day to historical morphological changes at sandy beaches world‐wide. The discussion highlights the influence of photographic scale, lens distortions, ground control points in segmented blocks, and the use of shoreline as a proxy of volumetric change. DSMs were derived using datasets obtained in 1946, 1966, 1971, 1977, 1986 and 2019, and compared to a 2007 LiDAR‐derived DSM. The emerging approach produced suitable DSMs for volumetric analysis, except for the 1946 dataset, which had the smallest scale and was significantly vertically offset. Volumetric losses of up to 60 m³/m of beach length were calculated for parts of Mounts Bay between 1977 and 2007, and up to 21 m³/m in recent years. At Apollo Bay, the construction of the port in the early 1950s significantly impacted the natural longshore drift to the beach. The adjacent stretch of coastline accreted at a rate of ~ 35 m³/m between 1966 and 2007, as a function of dredge disposal and changes in sediment transport, whereas a maximum volumetric loss of ~47 m³/m was detected further north between 1977 and 2007. A volume of ~71,330 ± 15,200 m³ was lost from the system from 2007 to 2019, despite the continued deposition along the northern section of the beach.
... Consequently, unmanned aerial vehicles (UAVs) are becoming valuable mapping and research tools in most branches of geomorphology (Gomez-Gutierrez et al., 2014;Immerzeel et al., 2014;Lucieer et al., 2014;Prosdocimi et al., 2015;Cook, 2017;Dąbski et al., 2017;Rossini et al., 2018). In coastal regions UAVs have been used to monitor and map beaches, dunes, cliffs, rocky foreshores, and other coastal elements that often change very rapidly or are in areas that are difficult or dangerous to access (Delacourt et al., 2009;Gonçalves and Henriques, 2015;Trenhaile, 2015a, 2015b;Autret et al., 2016;Casella et al., 2016;Ierodiaconou et al., 2016;Castelle et al., 2017;Sturdivant et al., 2017). ...
... It also uses a different methodology from the previous work by Perez-Alberti and Trenhaile (Pérez-Alberti and Trenhaile, 2015a, Pérez-Alberti andTrenhaile, 2015b), being based on photogrammetric analysis of two high resolution (1.8 cm) digital surface models (DSMs) of the entire study area. This procedure, which has previously been applied to sandy beaches (Ierodiaconou et al., 2016), allows the data to be processed semi-automatically, thereby reducing the processing time and facilitating repetition of the analytical procedures and their application to other areas of study. ...
An unmanned aerial vehicle (UAV) was flown over a boulder beach (area 20,000 m²) on the southern coast of Galicia (northwestern Spain) in May 2016, continuing earlier work based on flights over the same beach in July 2012, May 2013, and late March 2014. Digital Surface Models (DSMs) with 1.8 cm resolution were constructed from the 2014 and 2016 data to identify changes in beach morphology over the intervening period. Analyses were conducted using a Limit of Detection (LoD) of 0 cm and 3.71 cm. In both cases, the analyses showed that erosion dominated over 19 % of the beach area. Accretion occurred over the rest of the beach, which acquired an additional 1500 m³ of material over the study period. Re‐analysis of the data from earlier flights suggested that erosion dominated on the beach in 2012‐2013 and deposition in 2013‐2014. Without any clear relationship between beach behaviour and storm severity during each winter period, it is proposed that gravitationally induced erosion and storm‐wave induced deposition are the result of perturbations about an equilibrium beach gradient. The UAV data also suggested that an essentially random component modulates regional patterns of movement.
... Alternatively, very high-spatialresolution (<10 cm) multispectral imagery derived from unoccupied aerial vehicles (UAVs) (also known as unmanned aerial vehicles) can be collected multiple times during a growing season at the temporal discretion of the user [63,64]. This is important in coastal environments where complex factors, such as seasonal phenology, tidal cycles, and storm events, may influence the spectra of the targets being imaged [65][66][67]. ...
New England salt marshes provide many services to humans and the environment, but these landscapes are threatened by drivers such as sea level rise. Mapping the distribution of salt marsh plant species can help resource managers better monitor these ecosystems. Because salt marsh species often have spatial distributions that change over horizontal distances of less than a meter, accurately mapping this type of vegetation requires the use of high-spatial-resolution data. Previous work has proven that unoccupied aerial vehicle (UAV)-acquired imagery can provide this level of spatial resolution. However, despite many advances in remote sensing mapping methods over the last few decades, limited research focuses on which spectral band, elevation layer, and acquisition date combinations produce the most accurate species classification mappings from UAV imagery within salt marsh landscapes. Thus, our work classified and assessed various combinations of these characteristics of UAV imagery for mapping the distribution of plant species within these ecosystems. The results revealed that red, green, and near-infrared camera image band composites produced more accurate image classifications than true-color camera-band composites. The addition of an elevation layer within image composites further improved classification accuracies, particularly between species with similar spectral characteristics, such as two forms of dominant salt marsh cord grasses (Spartina alterniflora) that live at different elevations from each other. Finer assessments of misclassifications between other plant species pairs provided us with additional insights into the dynamics of why classification total accuracies differed between assessed image composites. The results also suggest that seasonality can significantly affect classification accuracies. The methods and findings utilized in this study may provide resource managers with increased precision in detecting otherwise subtle changes in vegetation patterns over time that can inform future management strategies.
... Unoccupied Aerial Vehicle (UAV) surveys using a DJI Phantom 4 Pro and RTK models, with RTK-GPS ground control points, were undertaken every 6-8 weeks from June 2018 until December 2022 (see Pucino et al. (2021a) and Ierodiaconou et al. (2022) for methodological detail). All imagery was processed into digital surface models using Structure-from-Motion techniques (Westoby et al., 2012) and subsequently analysed in ArcMap (Ierodiaconou et al., 2016). Transects at 30 m spacing were cast across all images to analyse shoreline change. ...
... Volumetric analysis was conducted by computing Digital Elevation Models (DEM) of Difference (DoD) between UAV DSMs. A limit of detection (LoD) approach (Ierodiaconou et al., 2016;Gómez-Pazo et al., 2019) has been used to take DSM errors into consideration during volumetric analysis. The median absolute deviation (NMAD) is used as a robust estimator for elevation precision that has been derived from a wider dataset for various sites across the Victorian Coast (Pucino et al., 2021), giving a global median LoD value of 0.05 m. ...
Understanding the drivers of coastal change is important for establishing how a system behaves and responds under different conditions, which is then used for informing management interventions. At seasonal to decadal scales this ideally requires long periods of repeat and frequent monitoring to detect changes in, for instance, shoreline position and beach volume. In this study, we analysed just two years of unmanned aerial vehicle (UAV) surveys over a single eroding beach-dune system (Victoria, Australia), in order to assess its utility in understanding the drivers of change. This morphological data was combined with a WAVEWATCH III (CAWCR) model hindcast, that was assessed against a newly installed, portable, wave buoy. Between August 2018–2020, net shoreline recession, at a rate of 3.1 m/year and net erosion volume change of 1736 m3 occurred along Main Beach in Inverloch. Negative correlations were found between coastal change metrics and wave height, wave direction and rougher sea states. Stronger correlations were found between oceanic conditions and volumetric change than with shoreline change. Beachface changes at this scale have a more instantaneous response to driving conditions, whereas the shoreline reflects longer-term patterns and the impact of extreme events. Spatial and temporal variations were evident, resulting from increasing wave exposure from west to east along the coast, geological controls, human interventions, and variable wave and storm patterns. Strong seasonal patterns were identified in rates of coastal change; however, these changes were offset by the most energetic wave and storm seasons due to morphological hysteresis and the relative change in magnitude of waves or frequency of storms between seasons. The data prove that studies over short period and spatial scales can be highly effective in understanding the drivers of beach change. These findings allow managers to have confidence that small datasets can be highly useful for sound planning strategies.
... We mitigated this systematic error by removing vegetation and applying specific limits of detection thresholds, which is a form of split data test 46 used to obtain the expected DSMs vertical errors by computing the elevation difference between pre-and post-survey pairs over known stable areas (i.e. calibration areas 22 ). ...
Sandy beaches are highly dynamic systems which provide natural protection from the impact of waves to coastal communities. With coastal erosion hazards predicted to increase globally, data to inform decision making on erosion mitigation and adaptation strategies is becoming critical. However, multi-temporal topographic data over wide geographical areas is expensive and time consuming and often requires highly trained professionals. In this study we demonstrate a novel approach combining citizen science with low-cost unmanned aerial vehicles that reliably produces survey-grade morphological data able to model sediment dynamics from event to annual scales. The high-energy wave-dominated coast of south-eastern Australia, in Victoria, is used as a field laboratory to test the reliability of our protocol and develop a set of indices to study multi-scale erosional dynamics. We found that citizen scientists provide unbiased data as accurate as professional researchers. We then observed that open-ocean beaches mobilise three times as much sediment as embayed beaches and distinguished between slowed and accelerated erosional modes. The data was also able to assess the efficiency of sand nourishment for shore protection. Our citizen science protocol provides high quality monitoring capabilities, which although subject to important legislative preconditions, it is applicable in other parts of the world and transferable to other landscape systems where the understanding of sediment dynamics is critical for management of natural or anthropogenic processes.
... Drone-based citizen science has started organically with, for example, recordings of informative marine animal behaviours or submission of shark sightings via apps. There are now bespoke drone-based citizen science programs such as the Victorian Coastal Monitoring Program, which has more than 120 citizen scientists engaged in flying drones to map and monitor coastal change [170]. We recommend in areas where drones are already being used recreationally (e.g., along beaches) that scientists explore the potential of citizen scientists. ...
The use of drones to study marine animals shows promise for the examination of numerous aspects of their ecology, behaviour, health and movement patterns. However, the responses of some marine phyla to the presence of drones varies broadly, as do the general operational protocols used to study them. Inconsistent methodological approaches could lead to difficulties comparing studies and can call into question the repeatability of research. This review draws on current literature and researchers with a wealth of practical experience to outline the idiosyncrasies of studying various marine taxa with drones. We also outline current best practice for drone operation in marine environments based on the literature and our practical experience in the field. The protocols outlined herein will be of use to researchers interested in incorporating drones as a tool into their research on marine animals and will help form consistent approaches for drone-based studies in the future.
... The elevation of each MEM site at Lorne was surveyed using a total station and the relative heights have been reduced to the Australian Height Datum (AHD) (mean sea level) using available geodetic survey benchmarks. The Marengo profile was generated by using a UAV (unmanned aerial vehicle) -PPK (postprocessing kinematic) -SfM (structure-from-motion) workflow (Ierodiaconou et al., 2016;Zhang et al., 2019). A vertical accuracy of 20 mm was calculated through comparison of the UAV to the total station surveys at Lorne. ...
Knowledge of the spatial pattern of erosion on shore platforms is needed to better understand their evolution. The long-term spatial and temporal variation of downwearing remains difficult to interpret from erosion data commonly collected over 1–3 years of monitoring. We report erosion data recorded with a micro-erosion meter (MEM) over 40 years (1979–2019) on sandstone shore platforms in a micro-tidal environment along the Otway coast, Victoria, Australia. This well-preserved monitoring network (43 out of 44 original MEM sites) allowed a detailed investigation over a multidecadal timescale not previously considered. Over 40 years the mean erosion rate was 0.25 mm/yr. This value was statistically similar to erosion rates calculated over 2-year (0.32 mm/yr) and 32-year (0.26 mm/yr) periods. In the vertical plane, two significant but opposite relationships between elevation and erosion rates were displayed in the central intertidal zone. There was also a peak in the erosion rate near mean higher high water level. This spatial pattern was strongly associated with wetting and drying controlled by tides and waves. At elevations lower than mean higher low water, downwearing rates were one or two orders of magnitude lower than the average rate of the entire platform. The low erosion rates may be caused by the longer wetting condition of surfaces at lower elevation. Fast erosion rates were recorded in the upper intertidal zone where the bedrock was only inundated by spring high tides or storm waves. Salt weathering may be the primary mechanism but the effect of thermal weathering cannot be neglected at higher elevation. Based on the experience from the near complete MEM network in the study area, suggestions were provided to extend the longevity of monitoring network for future long-term erosion records on shore platforms.
... 8,18,26 Therefore, in the present study, the Pix4D software was used to apply the SfM algorithm to create multi-temporal 3D dense point clouds, mesh models, very high-resolution DSMs and to model the morphodynamic processes in the meandering structures along the BMR by processing the images taken by UAVs. 41,42 SfM photogrammetric measurement steps were performed in order to map overlapping images, derive dense point clouds, create 3-D network models over dense point clouds, and produce high resolution orthomosaics and digital elevation models (DEMs). 43,44 DEM is a generic term that covers digital topographic data in all its various forms as well as the method for interpreting implicitly of the elevations between observations. ...
Change detection analysis for monitoring and modeling riverine systems requires
detailed spatial and temporal surveying of river morphology dynamics. Accurate digital surface
models are an essential part of the studies of morphodynamic modeling of rivers and river channel evolution. An accurate high-resolution surface model of the river channel and floodplain
enables a more comprehensive view of the riverbed evolution and allows monitoring of morphological changes of the entire river channel more precisely compared with traditional methods.
In current practice, unmanned aerial systems (UAS) are widely used for various applications in
photogrammetry, especially for three-dimensional surface modeling and large-scale mapping of
riverine environments. UASs offer many advantages in terms of cost and image resolution and
approaches for mapping across varying spatial extents when compared with terrestrial photogrammetry and satellite remote sensing systems. UAS-based aerial mapping was implemented in
order to produce very high resolution surface models of a flood-sensitive region based on structure from motion technique. Ultimately, multitemporal topographic data were produced, and
morphodynamic processes in the lower course of the Büyük Menderes River in Turkey were
modeled by digital shoreline analysis system and digital elevation model of difference methods.
These methods were employed to examine the changes in the shoreline and to analyze the size of
geomorphological changes and spatial patterns. The results showed that the change in the shoreline of the meanders varied from 3 to 27 m, and the water levels varied between ∼0.3 and 3 m.
Although there was both sediment erosion and deposition along the shoreline, the predominant
process was identified as deposition in the shoreline. A significant correlation was found
between the deposited sediments and the sinuosity index values (r=0.88) according to the
changes in water level over the months. In addition, major changes on the deposition rate were
found to occur mostly after the summer season. This research showed that UASs could provide
a suitable measurement model for determining areal and volumetric eroded/deposited sediment
quantities along the meandering fields.
... A number of ecological and environmental monitoring studies have been published that demonstrate the costeffectiveness of drones as a rapid and versatile spatio-temporal monitoring platform in preference to other traditional techniques (for summary of the benefits of drones over traditional aerial surveys (see Hodgson et al. 2013). In relation to marine monitoring, drones have been used for two-dimension habitat mapping (Joyce et al. 2018), detecting change (Ruwaimana et al. 2018), three-dimensional habitat complexity models, sea surface temperature (SST) observations (Casella et al. 2017), animal physiological and ecological monitoring of megafauna (Hodgson et al. 2013, Christiansen et al. 2018, and geomorphological modelling and coastal change detection (Ierodiaconou et al. 2016). ...
A suite of field manuals was released by the NESP Marine Hub in early 2018 to facilitate a
national monitoring framework, with a focus on seven marine sampling platforms: multibeam sonar, autonomous underwater vehicles, baited remote underwater video (pelagic and demersal), towed imagery, sleds and trawls, and grabs and box corers. These platforms were identified based on frequency of use in previous open water sampling and monitoring programs. Stakeholder feedback revealed several key sampling platforms and data types not included in the original release, as well as a possible need for field manuals related to cultural or socioeconomic standard operating procedures (SOPs).
The current report scopes the need and feasibility of developing new field manuals as related to monitoring Australia’s waters for the following:
• Remote operating vehicles (ROVs)
• Passive acoustic monitoring (PAM)
• Sub-bottom profiling (SBP)
• Drones
• Satellite imagery
• Marine plastics
• Environmental DNA (e-DNA)
• Plankton
• Sampling for Sea Country
• Socioeconomic monitoring
Based on recommendations provided here, an ROV field manual seems necessary and
achievable for the NESP Marine Hub program in 2019-2020, while the new NESP Project D6 will provide foundations in 2019-2020 from which a new SOP on socioeconomic monitoring may eventuate. A further six SOPs and associated field manuals may be developed in the future (UVC, PAM, SBP, drones, e-DNA, plankton), assuming suitable resources are secured, including a champion to chair a collaborative working group and lead the development of a field manual.
Recommendations from this report indicate that three of the scoped SOPs are not needed, either due to a scope too broad to allow a national SOP (satellite imagery) or other initiatives that are already in advanced development stages (marine plastics, sampling for Sea Country).
... The newest techniques, often involving Structure from Motion-Multi View StereoScan (SfM-MVS onwards) and UAVs, produce low cost and high quality-quantity topographical information. This technology plays a key role in assessing, monitoring, and analysing global change and, accordingly, there has been an exponential increase in their use in the geomorphological disciplines, including mass movements (Turner et al., 2015;Abellán et al., 2014;Lucieer et al., 2014;Daehne and Corsini, 2013;Niethammer et al., 2012;Prokop and Panholzer, 2009;Baldi et al., 2008) and coasts (Castelle et al., 2017;Sturdivant et al., 2017;Autret et al., 2016;Casella et al., 2016;Ierodiaconou et al., 2016;Turner et al., 2016;Gonçalves and Henriques, 2015;Trenhaile, 2015a, 2015b;Harwin and Lucieer, 2012;Delacourt et al., 2009). ...
Historical air photographs, LiDAR, and an unmanned aerial vehicle (UAV) were used to record the movement, from 1956 to 2018, of a clay and clast earthflow in a coastal valley in northwestern Spain. Two procedures were employed. The first tracked changes, in a GIS environment, in the location of eight, easily identified objects on the surface of the deposit (large boulders, topographic lobes, and the foundations of an old hut). The second used DEMs of Difference (DoDs) based on Digital Elevation Models from a 2011 LiDAR flight and two UAV flights in 2016 and 2018 obtained by Structure from Motion-Photogrammetry techniques. While the first procedure provided estimates for earthflow movement over a 62-year period, the second produced more precise data for periods of up to 8-years. The first procedure indicated that the mean rate of movement was 0.48 m•yr-1, increasing from only 0.14 m•yr-1 from 1956 to 1983 to between 0.50 and 0.83 m•yr-1 from 1983 to 2018. Despite some temporal and spatial changes in direction, rates of surface movement were quite uniform on the deposit. The increase in earthflow movement after 1983 may be related to an increase in rainfall, although human activities associated with the removal of a wrecked ship from the nearshore may have been a contributing factor. The role of debuttressing due to the wave-induced removal of lateral support from the toe of the deposit is less clear. While there was no clear relationship between wave erosion and rates of movement, coastal retreat may have triggered changes in the direction and sediment flux in the toe of the deposit. This effect could have been tempered by negative feedback, however, whereby coastal erosion and increased flow activity were countered by the protection afforded by the accumulation of large, dislodged boulders on the beach. Because of this feedback, it is difficult to predict the impact of sea level rise and other elements of climate change along this coast.
... In recent years, the SFM technique has been used to generate high resolution digital terrain models and orthophoto maps by processing images obtained from UAV through commercial softwares. Therefore, in the scope of the study, the Pix4D software was used to apply the SfM algorithm to create multi-temporal 3D dense point clouds, mesh models, very high-resolution digital surface models and to model the morphodynamic processes in the meandering river by processing the images taken by UAVs [11,12]. ...
... In recent years, the SFM technique has been used to generate high resolution digital terrain models and orthophoto maps by processing images obtained from UAV through commercial softwares. Therefore, in the scope of the study, the Pix4D software was used to apply the SfM algorithm to create multi-temporal 3D dense point clouds, mesh models, very high-resolution digital surface models and to model the morphodynamic processes in the meandering river by processing the images taken by UAVs [11,12]. ...
... low tide; see Casella et al. 2017) or before and after events (e.g. storms; see Ierodiaconou et al. 2016). Where in-water surveys are limited in their coverage, drones can survey significantly larger areas while still providing high-resolution information, with the added benefit of being spatially explicit and highly replicable (Hamylton 2017b). ...
With almost limitless applications across marine and freshwater environments, the number of people using, and wanting to use, remotely piloted aircraft systems (or drones) is increasing exponentially. However, successfully using drones for data collection and mapping is often preceded by hours of researching drone capabilities and functionality followed by numerous limited-success flights as users tailor their approach to data collection through trial and error. Working over water can be particularly complex and the published research using drones rarely documents the methodology and practical information in sufficient detail to allow others, with little remote pilot experience, to replicate them or to learn from their mistakes. This can be frustrating and expensive, particularly when working in remote locations where the window of access is small. The aim of this paper is to provide a practical guide to drone-based data acquisition considerations. We hope to minimise the amount of trial and error required to obtain high-quality, map-ready data by outlining the principles and practice of data collection using drones, particularly in marine and freshwater environments. Importantly, our recommendations are grounded in remote sensing and photogrammetry theory so that the data collected are appropriate for making measurements and conducting quantitative data analysis.
Coasts are highly dynamic systems. Understanding how they respond to individual storms events and to future climate change is difficult as local boundary conditions determines their evolutionary trajectory. A lack of field data at this local scale therefore limits the ability of managers and researchers to apply existing modelling frameworks to their region of interest to ensure preservation of the natural environment. Data acquisition through low-cost Unoccupied Aerial Vehicles (UAVs) has become a viable means for obtaining high-resolution surveys (cm-scale) on the coast for whole sediment compartments (km-scale). A continued limitation however is the intensive labour costs involved in data acquisition. Here we show the power of Citizen Science in providing high quality, cost-effective data collection, when provided with adequate training and resources along a high-energy, temperate coast in Victoria, Australia. This was conducted through the Victorian Coastal Monitoring Program (VCMP), formed in 2018 as a collaboration between Australian universities and the Victorian State Government. As of 2022, this program covered 28 sites, with over 450 individual surveys taken at 6–8 week intervals. The VCMP has guided and driven significant management actions on the coast from realignment of coastal walking paths for public safety to measuring sand renourishment success. In this paper we (i) present the Citizen Science UAV program methodology, as an example that can be replicated in other jurisdictions, and (ii) illustrate, through a case-study of a sandy beach and rocky cliff, the benefits and precision achievable using our Citizen Science approach. We outline how outputs can be made widely available and applied to coastal management, with the aid of data portals and decision support systems. This data accessibility has been central to our community engagement, enabling citizen scientists to conduct their own bespoke analysis for co-creation of management solutions for their local area. It was also found to be key for facilitating continued community engagement during one of the world's longest lockdowns of the COVID-19 pandemic, impacting the program for almost two years.
Two aerial surveys were processed with Structure from Motion -
Multiview-Stereo with a Co-Alignment approach in two sectors of
a wetland: El Picaflor (EP) and El Sarand�ı (ES). Shoreline changes
were analysed with Digital Shoreline Analysis System (DSAS) using
high-resolution orthophotos and change detection was calculated
with M3C2. In EP the shoreline changes rate averages �0.71 m/yr
and the M3C2 comparison shows that the coast is mainly erosional.
In ES the shoreline rates of change averages 0.59 m/yr and
the M3C2 comparison shows both erosion and deposition. When
EP and ES were compared, the main differences are land use,
orientation of the coast, and the presence of intertidal vegetation.
The use of the Co-Alignment approach together with DSAS
proves to be a valuable technique for monitoring shoreline
changes at a high spatial and temporal resolution in this wetland
and can be applied to study other coastal wetlands worldwide.
Shore platforms evolve over millennial scales but understanding precisely how instantaneous processes scale over these longer periods is a major scientific quandary. A reason for this, is that erosion often occurs on the granular scale and measurement of magnitude and frequency of this decay is difficult. Over the past 50 years, a number of techniques have been used to quantify the micro-scale (0.01–10 mm) erosion of coastal bedrock, from direct surface contact techniques to those which involve remote sensing. The micro-erosion meter (MEM) and traversing micro-erosion meter (TMEM) are the most common techniques, recording erosion rates from <0.1 to 5 mm/yr on rock surfaces of c. 50 cm². The traversing erosion beam (TEB) is specifically designed to measure rapid erosion (> 10 mm/yr) while the Swantesson laser scanner (SLS) and close-range Structure-from-motion (SfM) photogrammetry have been used for observation of larger rock surfaces of 0.2 m². The rock tablet method is used to investigate the individual processes operating on downwearing. By comparing their advantages and disadvantages, the T/MEM is suggested to continue to play an important role in monitoring surface lowering in conditions where the total erosion is 20 mm over the monitoring period, with close-range SfM recommended as ideal for quantifying erosion of 2–50 mm. However, all the instruments are biased in the field conditions under which they can be operated, and it is important for researchers to contextualise their measured surfaces in regards to a whole platform. Future studies will benefit from the combination of the ground-based methods with new techniques that provide finer morphological features at the regional scale or interpret the evolution of shore platforms over long timescales.
The coastal zone is extremely active, where multiple geodynamic agents converge, contributing to its constant morphological evolution. One of the most common coastal forms are cliffs, where it occurs mass movements that contribute to the change of its profile, representing a high risk for people and goods, both at its top and base. The evolution of coastal cliffs is spatially different and it is the result of a combination of various factors – such as morphology, rock strength, exposure of slopes and the action of erosive agents – which determine their stability.
In the context of coastal risk prevention and spatial planning, the monitoring of cliffs plays a key role in monitoring their dynamics, trends, and geomorphological changes. This work aims to present a low-cost experimental methodological approach, applied at a municipal level which, combining the use of an unmanned aircraft (UAS) with the application of the Structure-from-Motion with Multi-View Stereo (SfM-MVS) photogrammetry technique, allows to safely check for signs of instability and anticipate dangerous events; obtain high resolution and accurate cartographic data often; determine and quantify the changes occurred in a certain period; and, in a medium/long term, assess the cliff retreat rate and contribute to the identification of patterns that promote coastal erosion.
The results accomplished demonstrate the potential of this methodology. It contributes to the management of the coast and support the decision making. Through the products generated, the results prove the effectiveness and decimetric precision obtained, highlighting the dynamics of the coastline of the municipality of Torres Vedras.
Several occurrences of mass movements were recorded in a short period time, revealing signs of instability that during the bathing season can result in a high risk for exposed vacationers, demonstrating the importance of implementing a regular coastal monitoring plan.
Morphological changes, caused by the erosion and deposition processes due to water discharge and sediment flux occur, in the banks along the river channels and in the estuaries. Flow rate is one of the most important factors that can change river morphology. The geometric shapes of the meanders and the river flow parameters are crucial components in the areas where erosion or deposition occurs in the meandering rivers. Extreme precipitation triggers erosion on the slopes, which causes significant morphological changes in large areas during and after the event. The flow and sediment amount observed in a river basin with extreme precipitation increases and exceeds the long-term average value. Hereby, erosion severity can be determined by performing spatial analyses on remotely sensed imagery acquired before and after an extreme precipitation event. Changes of erosion and deposition along the river channels and overspill channels can be examined by comparing multi-temporal Unmanned Aerial Vehicle (UAV) based Digital Surface Model (DSM) data. In this study, morphological changes in the Büyük Menderes River located in the western Turkey, were monitored with pre-flood (June 2018), during flood (January 2019), and post-flood (September 2019) UAV surveys, and the spatial and volumetric changes of eroded/deposited sediment were quantified. For this purpose, the DSAS (Digital Shoreline Analysis System) method and the DEM of Difference (DoD) method were used to determine the changes on the riverbank and to compare the periodic volumetric morphological changes. Hereby, Structure from Motion (SfM) photogrammetry technique was exploited to a low-cost UAV derived imagery to achieve riverbank, areal and volumetric changes following the extreme rainfall events extracted from the time series of Tropical Rainfall Measuring Mission (TRMM) satellite data. The change analyses were performed to figure out the periodic morphodynamic variations and the impact of the flood on the selected meandering structures. In conclusion, although the river water level increased by 0.4–5.9 meters with the flood occurred in January 2019, the sediment deposition areas reformed after the flood event, as the water level decreased. Two-year monitoring revealed that the sinuosity index (SI) values changed during the flood approached the pre-flood values over time. Moreover, it was observed that the amount of the deposited sediments in September 2019 approached that of June 2018.
There is currently little understanding regarding storm surge in New Zealand, particularly in the southern region. To date, there has been no attempt to establish the frequency and magnitude of storm surge using observed sea level data on the open coast. The aim of this study is to examine the nature of storm surge in southern New Zealand and explore the influence of the Southern Annular Mode (SAM) and the El Nino Southern Oscillation (ENSO) on the frequency and magnitude of storm surge. Bayesian estimation is used through the ‘extRemes’ package in R to determine the return period for storm surge at three locations around southern New Zealand. The 100-year return level varied between 0.91 and 1.31 m. In addition, a statistically significant increase (2.88%) in storm surge intensity (SSI) on the south-east coastline was found. Applying cross-correlation to assess the response of SSI to ENSO and SAM, returned no detectable relationship, except a weak relationship between SAM and SSI on the south-east coast where a two-three month lagged response was present.
• Intertidal habitat maps are needed at both fine and coarse scales to monitor change and inform conservation and management, but current methods of field survey and expert interpretation of aerial imagery can be time‐consuming and subjective. Object‐based image analysis (OBIA) of remote sensing data is increasingly employed for producing habitat or land cover maps. Users create automated workflows to segment imagery, creating ecologically meaningful objects, which are then classified based on their spectral or geometric properties, relationships to other objects and contextual data.
• This study evaluates the change‐detection capability of OBIA in the intertidal environment by developing and comparing two OBIA methods for quantifying change in extent and distribution of habitats from freely available multi‐temporal aerial imagery and LiDAR data. Despite considerable variability in the data, pre‐ and post‐classification change detection methods had sufficient accuracy (mean overall accuracy from 70.5 to 82.6%) to monitor deviation from a background level of natural environmental fluctuation.
• This insight into spatial and temporal patterns of natural cyclical change and their detectability by OBIA could inform use of remote sensing for regular, rapid coastal assessment, providing an alert system to direct survey resources to areas of ecologically relevant change.
Beaches are characterized by high morphodynamic activity, and high-frequency measurements are needed to understand their states and rates of change. Ideally, beach survey methods should be at once accurate, rapid and low-cost. Recently, unmanned aerial systems (drones) have been increasingly utilized to measure beach topography. In this paper, we present a review of the state of art in drones and photogrammetry for beach surveys and the respective achieved measurement quality (where reported). We then show how drones with a minimal configuration and a low-cost setup can meet the high accuracy and rapidity required for beach surveys. To test a minimal drone and ground control point configuration, we used consumer-grade equipment to perform the same flight path with different cameras and at different altitudes. We then used photogrammetry to produce digital elevation models of the beach. Using a GNSS-RTK system, we collected 2950 independent control points to evaluate the accuracy of the digital elevation models. Results show that, once a few potential sources of uncertainties in the final digital elevation model are taken into account, the average RMSE(z) of the digital elevation models was ~5 cm, with a survey efficiency of ca. 3 m² min⁻¹. Digital elevation models taken at different times were used to calculate the before–after sediment budget following a storm that hit a sandy coast in Sylt Island at the German North Sea coast.
A State-of-the-Art of scientific literature related with Beach geomorphology is presented, from utilization of Tree of Science® tool - ToS. In a search done in November 2016, 73 papers were found in the Web of Science® with the combination of words ‘beach’ and ‘geomorphology. Papers were classified by ToS in roots (high input degree; n=5), trunks (high intermediation degree; n=10) and leaves (high output degree; n=58). Geomorphology was the most relevant journal, with 16 articles published (21.05%), which help to Elsevier to be the most relevant publisher in this topic (n=37; 48.7%). About authors, Helmut Brückner was the most relevant author, with a high number (3) of papers revised. Analysis of countries of authors’ affiliation shows a clear leading of United States (n = 80; 28%), followed by Germany (n = 31; 11%) and United Kingdom (n = 28; 10%). A general overview allows to identify a growing ToS in Beach geomorphology, with some very strong references in leaves, and several others references without less attention by scientific community belonging to this topic. Finally, a prospective analysis from branches suggest that scientific community is researching around four subtopics (sedimentation processes, coastal dune vegetation, remote sensors and coastline erosion), which could be in the near future a new ToS in the forest of beach geomorphology theme.
In this introduction to the special issue on Photogeomorphology and Landscape Change, the guest editor and section editor team up to provide a background to the use of photography and imagery within geomorphology. The authors examine a range of approaches and applications within the geomorphology subfield (of photogeomorphology), where historical imagery (either in print as photographs or as digital images), such as postcards, books, archival collections, and so forth, are adopted for portrayal, comparison, and measurement of landscape alterations across both time and space. The uses have been myriad, as they are applied from a variety of approaches and represent a visual tool for assessment and quantification. Following a brief commentary on various approaches and applications, this introduction outlines papers contained as part of the special issue that represent a variety of current approaches and applications adopted within a photogeomorphological methodology to study landscape change. © 2016 Gebrüder Borntraeger Verlagsbuchhandlung, Stuttgart, Germany.
Remotely-sensed glaciological measurements can be expensive, and often involve a trade-off between resolution, scale, and frequency. In an attempt to overcome these issues we report on a case study in which two low-cost techniques were used to generate orthomosaic images and digital elevation models (DEMs) of an arctic glacier in two consecutive ablation seasons. In the first aerial survey we used an unmanned aerial vehicle (UAV) and acquired images autonomously, while in the second we used a piloted helicopter and acquired images manually. We present a preliminary assessment of accuracy and apply these data to measure glacier thinning and motion.
Models of seabed sediment mobilisation by waves and currents over Australia's continental shelf environment are used to examine whether disturbance regimes exist in the context of the intermediate disturbance hypothesis (IDH), whereby maximum biodiversity coincides with moderate levels of disturbance. Our study shows that it is feasible to model the frequency and magnitude of seabed disturbance in relation to the dominant energy source (wave-, tide- or cyclone-dominated shelf). Areas are mapped where the recurrence interval of disturbance events is comparable to the rate of ecological succession, which meets criteria defined for a disturbance regime. We focus our attention on high-energy, patch-clearing events defined as exceeding the Shields (bed shear stress) parameter value of 0.25. Using known rates of ecological succession for different substrate types (gravel, sand and mud), predictions are made of the spatial distribution of a dimensionless ecological disturbance (ED) index, given as: ED = FA(ES/RI), where ES is the ecological succession rate for different substrates, RI is the recurrence interval of disturbance events and FA is the fraction of the frame of reference (surface area) disturbed. Maps for the Australian continental shelf show small patches of seafloor where ED indicates the potential existence of disturbance regimes (and inferred greater biodiversity) distributed around the continent, on both the inner and outer shelf. The patterns are different for wave-dominated (patches on the outer shelf trending parallel to the coast), tide-dominated (patches crossing the middle-shelf trending normal to the coast) and cyclone-dominated (large oval-shaped patches crossing all depths) shelf environments. Only a small portion of the shelf (similar to 10%) is characterised by a disturbance regime as defined here.
In this study, we used an Unmanned Aerial Vehicle (UAV) to collect a time series of high-resolution images over four years at seven epochs to assess landslide dynamics. Structure from Motion (SfM) was applied to create Digital Surface Models (DSMs) of the landslide surface with an accuracy of 4-5 cm in the horizontal and 3-4 cm in the vertical direction. The accuracy of the co-registration of subsequent DSMs was checked and corrected based on comparing non-active areas of the landslide, which minimized alignment errors to a mean of 0.07 m. Variables such as landslide area and the leading edge slope were measured and temporal patterns were discovered. Volumetric changes of particular areas of the landslide were measured over the time series. Surface movement of the landslide was tracked and quantified with the COSI-Corr image correlation algorithm but without ground validation. Historical aerial photographs were used to create a baseline DSM, and the total displacement of the landslide was found to be approximately 6630 m3. This study has demonstrated a robust and repeatable algorithm that allows a landslide's dynamics to be mapped and monitored with a UAV over a relatively long time series.
Remotely sensed glaciological measurements can be expensive, often involving
a trade-off between resolution, scale, and frequency. We report on a case
study in which two low-cost techniques were used to generate digital
elevation models and orthomosaics of an Arctic glacier in consecutive
ablation seasons. In the first aerial survey we used an unmanned aerial
vehicle and acquired images autonomously. The following year we took
advantage of the helicopter used for site access, and were able to acquire
images manually, for little additional helicopter time. We present a
preliminary assessment of accuracy and apply these data to measure glacier
thinning and motion.
Ecologists need data on animal-habitat associations in terrestrial and aquatic environments to design and implement effective conservation strategies. Habitat characteristics used in models typically incorporate (1) field data of limited spatial extent and/or (2) remote sensing data that do not characterize the vertical habitat structure. Remote sensing tools that directly characterize three-dimensional (3-D) habitat structure and that provide data relevant to organism-habitat interactions across a hierarchy of scales promise to improve our understanding of animal-habitat relationships. Laser altimetry, commonly called light detection and ranging (lidar), is a source of geospatial data that can provide fine-grained information about the 3-D structure of ecosystems across broad spatial extents. In this review, we present a brief overview of lidar technology, discuss recent applications of lidar data in investigations of animal-habitat relationships, and propose future applications of this technology to issues of broad species-management and conservation interest.
A synthesis of some results obtained over the period 1979–1982 from a study of beach and surf zone dynamics is presented. The paper deals with the different natural beach states, the process signatures associated with these states, environmental controls on modal beach state, and the temporal variability of beach state and beach profiles.Hydrodynamic processes and the relative contributions of different mechanisms to sediment transport and morphologic change differ dramatically as functions of beach state, that is depending on whether the surf zone and beach are reflective, dissipative or in one of several intermediate states. Depending on beach state, near bottom currents show variations in the relative dominance of motions due to: incident waves, subharmonic oscillations, infragravity oscillations, and mean longshore and rip currents. On reflective beaches, incident waves and subharmonic edge waves are dominant. In highly dissipative surf zones, shoreward decay of incident waves is accompanied by shoreward growth of infragravity energy; in the inner surf zone, currents associated with infragravity standing waves dominate. On intermediate states with pronounced bar-trough (straight or crescentic) topographies, incident wave orbital velocities are generally dominant but significant roles are also played by subharmonic and infragravity standing waves, longshore currents, and rips. The strongest rips and associated feeder currents occur in association with intermediate transverse bar and rip topographies.Long-term consecutive surveys of different beaches with contrasting local environmental conditions provide the data sets for empirical—statistical assessment of beach mobility, direction of change and response to environmental conditions. Conditions of persistently high wave energy combined with abundant and/or fine grained sediment results in maintaining highly dissipative states which exhibit very low mobility. Relatively low mobility is also associated with persistently low-steepness waves acting on coarsegrained beach sediments. In such cases, the modal beach state is reflective. The greatest degree of mobility is associated with intermediate but highly changeable wave conditions, medium grained sediment and a modest or meager sediment supply. Under such conditions, the beach and surf zone tend to alternate among the intermediate states and to exhibit well-developed bar trough and rhythmic topographies. A good association is found between beach state and the environmental parameter where Hb is breaker height, is mean sediment fall velocity and T is wave period. Temporal variability of beach state reflects, in part, the temporal variability and rate of change of Ω, which, in turn depends on deep-water wave climate and nearshore wave modifications.
This article presents an environmental remote sensing application using a UAV that is specifically aimed at reducing the data gap between field scale and satellite scale in soil erosion monitoring in Morocco. A fixed-wing aircraft type Sirius I (MAVinci, Germany) equipped with a digital system camera (Panasonic) is employed. UAV surveys are conducted over different study sites with varying extents and flying heights in order to provide both very high resolution site-specific data and lower-resolution overviews, thus fully exploiting the large potential of the chosen UAV for multi-scale mapping purposes. Depending on the scale and area coverage, two different approaches for georeferencing are used, based on high-precision GCPs or the UAV’s log file with exterior orientation values respectively. The photogrammetric image processing enables the creation of Digital Terrain Models (DTMs) and ortho-image mosaics with very high resolution on a sub-decimetre level. The created data products were used for quantifying gully and badland erosion in 2D and 3D as well as for the analysis of the surrounding areas and landscape development for larger extents.
We present the development of a low-cost Unmanned Aerial Vehicle-Light Detecting and Ranging (UAV-LiDAR) system and an accompanying workflow to produce 3D point clouds. UAV systems provide an unrivalled combination of high temporal and spatial resolution datasets. The TerraLuma UAV-LiDAR system has been developed to take advantage of these properties and in doing so overcome some of the current limitations of the use of this technology within the forestry industry. A modified processing workflow including a novel trajectory determination algorithm fusing observations from a GPS receiver, an Inertial Measurement Unit (IMU) and a High Definition (HD) video camera is presented. The advantages of this workflow are demonstrated using a rigorous assessment of the spatial accuracy of the final point clouds. It is shown that due to the inclusion of video the horizontal accuracy of the final point cloud improves from 0.61 m to 0.34 m (RMS error assessed against ground control). The effect of the very high density point clouds (up to 62 points per m(2)) produced by the UAV-LiDAR system on the measurement of tree location, height and crown width are also assessed by performing repeat surveys over individual isolated trees. The standard deviation of tree height is shown to reduce from 0.26 m, when using data with a density of 8 points per m(2), to 0.15 m when the higher density data was used. Improvements in the uncertainty of the measurement of tree location, 0.80 m to 0.53 m, and crown width, 0.69 m to 0.61 m are also shown.
The Southern Australian continental margin is exposed to some of the largest waves of the global ocean, having been generated by Southern Ocean extra-tropical storms. Waverider buoy data from four buoys which span the full 3000 km length of the Southern Australian continental margin, supplemented with 10 years of numerical model output from the WAVEWATCH III wave model, have been used to describe the directional wave climate of the region. The buoy records include two records at the western end of the margin (a 10-year record from Rottnest Island, and an 8-year record from Cape Naturaliste); a 6-year record from Cape de Couedic in the central portion of the margin; and a record spanning 20 years from Cape Sorell, at the southeastern end of the margin. Cape Sorell exhibits the steepest waves, largest mean significant wave heights, and most westerly wave directions, indicating increased proximity to Southern Ocean wave generating storms. Rottnest exhibits the least steep, smallest mean significant wave heights, and most southerly wave directions, reflecting the greater distance from the Southern Ocean generating storms. All sites demonstrate highly energetic extreme events, particularly at Cape Sorell, and a predominance of swell over wind sea states.
A morphodynamic classification of surfzones, beaches and dunes of the microtidal, low- to high-energy southeast Australian coast is presented.The first section (A: Waves and beaches) briefly deals with the transformation of deep-water wave energy as it crosses the shelf, nearshore and surfzone. Depending on the deep-water wave characteristics and shelf and inshore morphology, resultant breaker wave energy may be high, moderate or low, and the accompanying beach surfzone morphodynamic state in fine to medium sand beaches either dissipative, intermediate or reflective. Dissipative beaches have wide surfzones with shore parallel bar(s) and channel(s) and predominantly shore-normal circulation; intermediate beaches are characterised by rip circulation, crescentic-transverse bars and megacusps; and reflective beaches by a barless surfzone and steep, cusped or bermed beach. Each beach form has a characteristic level of beach stability, zone of sediment storage and mode of beach and dune erosion.Landward aeolian sediment transport of swash-deposited sand (Section B) is dependent on the subaerial beach topography and the aerodynamic flow regime across that topography. Characteristic profile shapes are ascribed to each beach type (dissipative, intermediate and reflective). Aeolian sand transport rates are potentially highest on dissipative beaches, moderate on intermediate beaches and lowest on reflective beaches. These rates determine the potential size of foredunes which are correspondingly largest on dissipative beaches and smallest on reflective beaches. The combination of mode and frequency of beach/dune erosion, rates of aeolian sand transport, and foredune volume and morphology provide an explanation of the nature and morphology of landward-occurring, large-scale dune systems. Dissipative beaches are frequently characterised by large-scale transgressive dune sheets; intermediate, by a trend from large-scale parabolic dune systems (high-wave energy) to small-scale blowouts (low-wave energy); and reflective beaches by minimal dune development.
Foredunes are shore-parallel dunes formed by aeolian deposition within vegetation. Modern established foredunes are classified into five morphologic stages and the morphologies and processes of each is described. Stage 1 foredunes are well vegetated, symmetric, stable ridges characterised by stoss face and crest deposition. Stage 2 foredunes display minor erosional patches, 75–90% vegetation cover and slight lateral variation in deposition and erosion. Stage 3 foredunes are hummocky, have a 45–75% vegetation cover range, and display various scales of blowouts, concave stoss faces and steeper lee faces. Stage 4 foredunes are characterised by large-scale erosional features such as blowouts, sand sheets and high asymmetry. Stage 5 foredunes comprise poorly vegetated remnant knobs. Each stage is characterised by a set of erosional and depositional processes which produce generally distinctive sets of cross-strata. Sedimentary structures within examples of each foredune stage are examined. Stage 1 and 2 foredunes are dominated by simple, large-scale, convex, continuous strata. Stage 3 and 4 foredunes display increasingly variable sets of cross-strata and a greater degree of planar and trough cross-stratification. Wave-cut scarps, blowout structures and very steep lee slope bedding may be preserved. The internal sedimentary structures presented here, form the basis of a facies model for foredunes.
This paper reviews LiDAR ground filtering algorithms used in the process of creating Digital Elevation Models. We discuss critical issues for the development and application of LiDAR ground filtering algorithms, including filtering procedures for different feature types, and criteria for study site selection, accuracy assessment, and algorithm classification. This review highlights three feature types for which current ground filtering algorithms are suboptimal, and which can be improved upon in future studies: surfaces with rough terrain or discontinuous slope, dense forest areas that laser beams cannot penetrate, and regions with low vegetation that is often ignored by ground filters.
Cambridge Core - Oceanography and Marine Science - Introduction to Coastal Processes and Geomorphology - by Robin Davidson-Arnott
Cambridge Core - Oceanography and Marine Science - Coasts - by Colin D. Woodroffe
Measurement of landscape form is a fundamental technique for geomorphologists. A range of surveying equipment is available, with this chapter focussing on the common surveying systems encountered by researchers and students, namely engineer's/auto level, electronic distance meter, total station, and terrestrial laser scanner. The choice of which type of instrument is to be used in the field will depend on: (1) the accuracy required; (2) field conditions; (3) reliability of benchmarks; (4) instrument ruggedness; and (5) facilities for post-field data analysis. This chapter is not a substitute for a professional surveying degree, but aims to outline the basic principles of surveying for a geomorphological audience.
The Victorian Coastal DEM represents a multi-million dollar investment by the Victorian Government to consider climate change adaptation on the coast. In this project The Victorian Department of Sustainability and Environment (DSE) has collected high resolution elevation data in both the marine and terrestrial environments. Significant planning, surveying and processing has been undertaken to generate a seamless, state-wide coastal DEM. A combination of aerial, sea and land surveying techniques were used in the construction of the Victorian Coastal DEM. Multiple topographic LiDAR surveys were conducted in the
terrestrial environment. In the marine environment one of the largest single-season bathymetric LiDAR surveys ever undertaken covered the entire length of the State, some 2000 linear kilometres. In addition to these airborne surveys, multi-beam sonar was used to fill in gaps where bathymetric LiDAR was unsuitable for data acquisition.
The combination of surveying projects and technologies has involved considerable ground control, data analysis and integration processing. The ground control has been strategically identified to maintain the quality and accuracy of the integrated DEM. The data analysis primarily involved assessing the quality of data and the differences between adjacent topographic to topographic and topographic to bathymetric projects. Automated procedures were developed to integrate the adjacent project datasets.
The Coastal DEM spans a height range of 30m and includes elevations up to +10m and depths down to -20m relative to the Australian Height Datum (AHD). In area, the DEM includes 6,400km2 of topographic LiDAR coverage, 4,700km2 of bathymetric LiDAR coverage and 315km2 of multi-beam sonar coverage. What is likely to be the world’s largest seamless, state-wide, high-resolution coastal DEM is now being used to assess the impact of climate change in Victoria.
The effects of large floods on river morphology are variable and poorly understood. In this study, we apply multi-temporal datasets collected with small unmanned aircraft systems (UASs) to analyze three-dimensional morphodynamic changes associated with an extreme flood event that occurred from June 19-23, 2013 on the Elbow River, Alberta. We documented reach-scale spatial patterns of erosion and deposition using high-resolution (4-5 cm/pixel) orthoimagery and digital elevation models (DEMs) produced from photogrammetry. Significant bank erosion and channel widening occurred, with an average elevation change of -0.24 m. The channel pattern was re-organized and overall elevation variation increased as the channel adjusted to full mobilization of most of the bed surface sediments. To test the extent to which geomorphic changes can be predicted from initial conditions, we compared shear stresses from a 2D hydrodynamic model of peak discharge to critical shear stresses for bed surface sediment sizes. We found no relation between modeled normalized shear stresses and patterns of scour and fill, confirming the complex nature of sediment mobilization and flux in high magnitude events. However, comparing modeled peak flows through the pre- and post-flood topography showed that the flood resulted in an adjustment that contributes to overall stability, with lower percentages of bed area below thresholds for full mobility in the post-flood geomorphic configuration. Overall, this work highlights the potential of UAS-based remote sensing for measuring three-dimensional changes in fluvial settings and provides a detailed analysis of potential relationships between flood forces and geomorphic change. This article is protected by copyright. All rights reserved.
Low altitude flights by a micro-drone were made in 2012 and 2013 over two boulder beaches in northwestern Spain. Geographical information system software was used to map the data. Boulder outlines from the first flight were recorded on 4796 clasts at Laxe Brava and 2508 clasts at Oia. Changes in location were identified by overlaying these outlines on the 2013 images. About 17.5 % of the boulders (mean surface area 0.32 m2) moved at Laxe Brava and about 53 % (mean surface area 0.23 m2) at Oia. Most movement on both beaches was between the mid-tide to about 2 m above the high tidal level. The location and elevation of the highest points were also recorded on the 2012 images on 4093 boulders at Laxe Brava and 3324 boulders at Oia. These elevations were compared with the elevations at the same locations in 2013. The occurrence and scale of the elevational changes were generally consistent with changes in the boulder outlines. The study confirmed that boulder beaches can be cheaply and effectively monitored using high resolution, micro-drone technology. This article is protected by copyright. All rights reserved.
To understand and predict Earth-surface dynamics, scientists often rely
on access to the latest remote sensing data. Over the past several
decades, considerable progress has been made in the development of
specialized Earth observation sensors for measuring a wide range of
processes and features. Comparatively little progress has been made,
however, in the development of new platforms upon which these sensors
can be deployed. Conventional platforms are still almost exclusively
restricted to piloted aircraft and satellites. For many Earth science
research questions and applications these platforms do not yet have the
resolution or operational flexibility to provide answers affordably. The
most effective remote sensing data match the spatiotemporal scale of the
process or feature of interest. An emerging technology comprising
unmanned aircraft systems (UAS), also known as unmanned aerial vehicles
(UAV), is poised to offer a viable alternative to conventional platforms
for acquiring high-resolution remote sensing data with increased
operational flexibility, lower cost, and greater versatility (Figure 1).
Mosses, the dominant flora of East Antarctica, show evidence of drying in recent decades, likely due to the regional effects of climate change. Given the relatively small area that such moss beds occupy, new tools are needed to map and monitor these fragile ecosystems in sufficient detail. In this study, we collected low altitude aerial photography with a small multi-rotor Unmanned Aerial Vehicle (UAV). Structure from Motion (SfM) computer vision techniques were applied to derive ultra-high resolution 3D models from multi-view aerial photography. A 2 cm digital surface model (DSM) and 1 cm orthophoto mosaic were derived from the 3D model and aerial photographs, respectively. The geometric accuracy of the orthophoto and DSM was 4 cm. A weighted contributing upstream area was derived with the D-infinity algorithm, based on the DSM and a snow cover map derived from the orthophoto. The contributing upstream area was used as a proxy for water availability from snowmelt, one of the key environmental drivers of moss health. A Monte Carlo simulation with 300 realisations was implemented to model the impact of error in the DSM on runoff direction. Significant correlations were found between these simulated water availability values and field measurements of moss health and water content. In the future ultra-high spatial resolution DSMs acquired with a UAV could thus be used to determine the impact of changing snow cover on the health and spatial distribution of polar vegetation non-destructively.
[1] Previous flume-based research on braided channels has revealed four classic mechanisms that produce braiding: central bar development, chute cutoff, lobe dissection, and transverse bar conversion. The importance of these braiding mechanisms relative to other morphodynamic mechanisms in shaping braided rivers has not yet been investigated in the field. Here we exploit repeat topographic surveys of the braided River Feshie (UK) to explore the morphodynamic signatures of different mechanisms of change in sediment storage. Our results indicate that, when combined, the four classic braiding mechanisms do indeed account for the majority of volumetric change in storage in the study reach (61% total). Chute cutoff, traditionally thought of as an erosional braiding mechanism, appears to be the most common braiding mechanism in the study river, but was more the result of deposition during the construction of diagonal bars than it was the erosion of the chute. Three of the four classic mechanisms appeared to be largely net aggradational in nature, whereas secondary mechanisms (including bank erosion, channel incision, and bar sculpting) were primarily net erosional. Although the role of readily erodible banks in facilitating braiding is often conceptualized, we show that bank erosion is as or more important a mechanism in changes in sediment storage than most of the braiding mechanisms, and is the most important “secondary” mechanism (17% of total change). The results of this study provide one of the first field tests of the relative importance of braiding mechanisms observed in flume settings.
Unmanned aerial vehicles (UAVs) equipped with digital compact cameras can be used to map landslides quickly and at a high ground resolution. Images taken by a radio-controlled mini quad-rotor UAV of the Super-Sauze, France landslide have been used to produce a high-resolution ortho-mosaic of the entire landslide and digital terrain models (DTMs) of several regions. The UAV capability for imaging fissures and displacements on the landslide surface has been evaluated, and the subsequent image processing approaches for suitably georectifying the data have been assessed. For Super-Sauze, horizontal displacements of 7 to 55m between a high-resolution airborne ortho-photo of May 2007 and a UAV-based ortho-mosaic of October 2008 have been measured. Fixed areas of persistent deformation have been identified, producing fissures of different distributions and orientations comparable to glacial crevasses, and relating directly to the bedrock topography. The UAV has demonstrated its capability for producing valuable landslide data but improvements are required to reduce data processing time for the efficient generation of ortho-mosaics based on photogrammetric DTMs, in order to minimise georeferencing errors.
Between 1974 and 1976, a series of east-coast cyclones in the western Tasman Sea resulted in extensive coastal erosion along southeastern Australia. In many beach compartments, the backshore and incipient foredune were completely removed, and the sea cut back into the swale and/or second dune ridge. This occurred at Moruya Beach, where a profile monitoring program had been established in 1972-a program that continues to this day. Here we report field evidence describing the initial condition of the beach, its subsequent erosion (such that the position of the initial backshore became the foreshore), and how this foreshore became reconstituted as a backshore ultimately developing into the present foredune. Critical to the formation of the frontal dune was the presence of a broad backshore berm at an elevation of 2.3 to 2.8 m above local mean sea level (MSL). Achievement of this elevation did not, by itself, guarantee foredune development. Rather, there is also a width threshold to the berm, which at Moruya is at least 30 m. While the berm reached either this elevation (2.3 to 2.8 m) or width (> 30 m) on several occasions prior to the formation of the incipient foredune, it was only when both conditions were satisfied that the embryo foredune developed into an incipient foredune. This was in the late 1970s and early 1980s. Incremental vertical growth of the foredune took place over the next 15 years, from an elevation of ca. 3.0 m up to 5 in above MSL. Initially, the position of the newly accreted foredune was well seaward of its prestorm (1972) position, but in the last few years it has tended to migrate inland, though the geographic position of the mean and high water level intercepts have not migrated with it.
Development of a notch at the base of a cliff reduces cliff stability and often induces a collapse. Pleistocene limestone coastal cliffs of elevation 5?m in Kuro-shima, Ryukyu Islands, have a prominent notch with a depth of 3–4?m at their bases. Around these coastal cliffs, collapses different from previous studies of cliff collapses in the Ryukyu Islands were found; collapses in Kuro-shima have a horizontal failure surface. The horizontal failure surface, situated at the height of the failure surface corresponding to the retreat point of the notch, is bounded by vertical joints cutting the whole cliff and the reef flat in front of the cliff. Two types of horizontal failure surface were found, triangular and quadrangular; the distinction appears to depend on the angle between the vertical joints and the front face of the cliff. Prior to collapse, these cliffs appear to have been separated from the adjacent cliffs by the development of vertical joints. Consequently, a cliff that will collapse can be identified in advance; cliff instability is strongly dependent on the development of a notch. To study the effect of notch development on cliff collapse, the notch depth at which collapse occurs was calculated using stability analysis. Instability of a cliff increases with notch depth; collapse occurs at the horizontal failure surface when the ratio of the notch depth to the seaward length of the cliff is approximately 0·5–0·7 for a triangular failure surface, and 0·7–0·9 for a quadrangular failure surface. Copyright © 2010 John Wiley & Sons, Ltd.
Beach profiles have been surveyed at monthly intervals between 1972 and 1988 at Moruya on the South Coast of New South Wales, Australia. Four profile sites have been used as a data set to provide an understanding of changes to beach volume, width, and shape. Moruya beach represents a moderately high energy, microtidal environment, which responds in a dramatic way to major storm events such as those experienced in the mid-1970s. This study distinguishes between profile characteristics associated with such a period (erosion-dominated or EDP) compared with periods when accretion dominated (ADP) accompanied by foredune expansion in both height and width.
Repeat topographic surveys are increasingly becoming more affordable, and possible at higher spatial resolutions and over greater spatial extents. Digital elevation models (DEMs) built from such surveys can be used to produce DEM of Difference (DoD) maps and estimate the net change in storage terms for morphological sediment budgets. While these products are extremely useful for monitoring and geomorphic interpretation, data and model uncertainties render them prone to misinterpretation. Two new methods are presented, which allow for more robust and spatially variable estimation of DEM uncertainties and propagate these forward to evaluate the consequences for estimates of geomorphic change. The first relies on a fuzzy inference system to estimate the spatial variability of elevation uncertainty in individual DEMs while the second approach modifies this estimate on the basis of the spatial coherence of erosion and deposition units. Both techniques allow for probabilistic representation of uncertainty on a cell-by-cell basis and thresholding of the sediment budget at a user-specified confidence interval. The application of these new techniques is illustrated with 5 years of high resolution survey data from a 1 km long braided reach of the River Feshie in the Highlands of Scotland. The reach was found to be consistently degradational, with between 570 and 1970 m3 of net erosion per annum, despite the fact that spatially, deposition covered more surface area than erosion. In the two wetter periods with extensive braid-plain inundation, the uncertainty analysis thresholded at a 95% confidence interval resulted in a larger percentage (57% for 2004–2005 and 59% for 2006–2007) of volumetric change being excluded from the budget than the drier years (24% for 2003–2004 and 31% for 2005–2006). For these data, the new uncertainty analysis is generally more conservative volumetrically than a standard spatially-uniform minimum level of detection analysis, but also produces more plausible and physically meaningful results. The tools are packaged in a wizard-driven Matlab software application available for download with this paper, and can be calibrated and extended for application to any topographic point cloud (x,y,z). Copyright © 2009 John Wiley & Sons, Ltd.
There are billions of photographs on the Internet, comprising the largest and most diverse photo collection ever assembled.
How can computer vision researchers exploit this imagery? This paper explores this question from the standpoint of 3D scene
modeling and visualization. We present structure-from-motion and image-based rendering algorithms that operate on hundreds
of images downloaded as a result of keyword-based image search queries like “Notre Dame” or “Trevi Fountain.” This approach,
which we call Photo Tourism, has enabled reconstructions of numerous well-known world sites. This paper presents these algorithms and results as a first
step towards 3D modeling of the world’s well-photographed sites, cities, and landscapes from Internet imagery, and discusses
key open problems and challenges for the research community.
Recent developments in extreme values modelling have been used to develop a framework for determining the coastal erosion hazard on sandy coastlines. This framework quantitatively reproduced the extreme beach erosion volumes obtained from field measurements at Narrabeen Beach, Australia. This encouraging finding was achieved using Kriebel and Dean's [Kriebel, D.L. and Dean, R.G., 1993. Convolution method for time-dependent beach profile response. Journal of Waterway, Port, Coastal and Ocean Engineering, 119(2): 204–226.] simple beach erosion and accretion model. The method includes allowances for joint probability between all basic erosion variates including; wave height, period and direction, event duration, tidal anomalies and event spacing. A new formulation for the dependency between wave height and period has been developed. It includes the physical wave steepness limitation. Event grouping, where significantly more erosion can occur from two closely spaced storms is handled by temporally simulating the synthetic wave climate and the resulting beach erosion and accretion.
The US Army Corps of Engineers' Field Research Facility (FRF) at Duck, North Carolina, has collected approximately biweekly beach-nearshore profile data to 8-m depth and associated wave data since 1981. Sediment budget analysis was used to examine the medium-scale (years to a decade) variability of the beach-nearshore profile from 1981 to 1991. Significant changes occurred during four groups of energetic storm events during February/March of 1983, 1987, 1989 and December 1989. Each group was comprised of at least two storms within a period of less than 39 days both with Hmo > 4 m. During each storm group, offshore sediment movement caused a distinct outer bar to migrate offshore and grow in size resulting in an abrupt increase in the volume of sediment on the upper shoreface. The net profile changes were much larger than the changes due to single storms and the cumulative effect of the storms can be considered as one ‘event’. During these events, the first storm appears to have a destabilizing effect on the profile which has insufficient time to recover before the second (and subsequent) storm (s). As a result, several storms in quick succession are able to have a large impact on the morphology. The intervening periods between the groups of storm events (termed fairweather conditions) lasted up to 4 years. They are characterized by slow, but steady sediment redistribution (averaging 33 m3 m−1 year−1) from the upper shoreface (> 5 m depth) toward the shore, while the total sediment volume was effectively constant. The onshore feed of sediment was not significantly affected by individual storms during the fairweather conditions. These two processes of (1) morphologic change during groups of storm events and (2) the steady onshore feed of sediments from the shoreface during fairweather conditions appear to play an important role on medium- and long-term profile evolution at least at Duck.
Airborne laser scanning systems are opening new possibilities for surveys and documentation of difficult areas and objects, such as dense city areas, forest areas and electrical power lines. Laser scanner systems available on the market are presently in a fairly mature state of art while the processing of airborne laser scanner data still is in an early phase of development. To come from irregular 3D point clouds to useful representations and formats for an end-user requires continued research and development of methods and algorithms for interpretation and modelling. This paper presents some methods and algorithms concerning filtering for determining the ground surface, DEM, classification of buildings for 3D City Models and the detection of electrical power lines. The classification algorithms are based on the Minimum Description Length criterion. The use of reflectance data and multiple echoes from the laser scanner is examined and found to be useful in many applications.
Estimates of significant wave height and period, together with tidal current speed over a semi-lunar cycle, were used to predict the area on the Australian continental shelf over which unconsolidated sediment was mobilised (threshold exceedance). These sediment-entraining processes were examined independently to quantify their relative importance on the continental shelf. Using observed grain size data, mobilisation from swell waves occurred on ∼31% and tidal currents on ∼41% of the continental shelf. Swell wave energy is sufficient to mobilise fine sand (0.1 mm diameter) to a water depth of 142 m on the Otway Shelf near the western entrance to Bass Strait. Tidal currents in King Sound (northwest shelf) are capable of mobilising large areas of medium sand (0.35 mm diameter) 100% of the time. Superimposing the distribution of threshold exceedance by wave and tidal currents indicates that there are areas on the shelf where either wave-induced or tidal currents dominate, some areas where waves and tides are of relatively equal importance and still other areas where neither is significant. We define six shelf regions of relative wave and tidal energy: zero (no-mobility); waves-only, wave-dominated, mixed, tide-dominated and tides-only. Our results provide a predictive, process-based understanding of the shelf sedimentary system that has applications to marine engineering projects and to regional studies of pollution dispersal and accumulation where significant shelf sediment mobilisation is a factor.
Notches cut by waves are currently developing at the base of vertical coastal limestone cliffs in Okinawa, Japan. The cliff height varies from 3.0–22.1 m, and the maximum notch depth is 8.8 m. Many rectangular or cubic blocks, which appear to have originated from cliff failures, are found on platforms in front of the cliffs. On the flat top surface of the cliff, tension cracks often run parallel to the cliff face. The vertical face of the cliffs displays small undulations but no sliding striation, suggesting that cliff failures have been caused by toppling rather than by shearing or sliding. We use slope stability analysis to determine the critical condition for toppling failure. Physical and mechanical properties of the cliff material were first obtained from laboratory tests. The results indicate that the strength of limestone shows a scale effect, such that the strength decreases with increasing size of the test specimens. Based on this result, we estimated the strength of a rock mass corresponding to the size of the coastal cliff. Cliff stability was then analyzed using a cantilever beam model. Comparison of the stability analysis and the dimension of fallen blocks indicates that toppling failure is strongly associated with the development of notches and tension cracks.
Alexandre C. G. Schimel, Centre for Integrative Ecology, School of Life and Environmental Sciences
- Daniel Ierodiaconou
Daniel Ierodiaconou (corresponding author), Alexandre C. G. Schimel, Centre for Integrative Ecology,
School of Life and Environmental Sciences, Deakin University, Warrnambool VIC 3280, Australia;
e-mail: iero@deakin.edu.au
The accuracy of automatic photogrammetric techniques on Ultra-Light UAV imagery
- O Küng
- C Strecha
- A Beyeler
- J.-C Zufferey
- D Floreano
- P Fua
- F Gervaix
Küng, O., Strecha, C., Beyeler, A., Zufferey, J.-C., Floreano, D., Fua, P. & Gervaix, F. (2011): The
accuracy of automatic photogrammetric techniques on Ultra-Light UAV imagery.-Proceedings of
the International Conference on Unmanned Aerial Vehicle in Geomatics (UAV-g), Zurich, Switzerland, 14-16 September 2011.-ISPRS Archives 2012, Volume XXXVIII-1/C22.
- G-H Lee
- R J Nicholls
- W A Birkemeier
Lee, G-H., Nicholls, R. J. & Birkemeier, W. A. (1998): Storm-driven variability of the beach-nearshore
profile at Duck, North Carolina, USA, 1981-1991. -Marine Geology 148: 163 -177.
- J B Vincent
- L K Werden
- M A Ditmer
Vincent, J. B., Werden, L. K. & Ditmer, M. A. (2015): Barriers to adding UAVs to the ecologist's toolbox.
-Frontiers in Ecology and the Environment 13: 74 -75.