[Show abstract][Hide abstract] ABSTRACT: An operational satellite-based approach was implemented to monitor turbidity and organic absorption in the Mekong river system. Using physics-based algorithms linked together in a fully automated processing chain, more than 300 Landsat Enhanced Thematic Mapper (ETM) scenes and 1000 MODIS scenes, representing five years of data, were used to produce standardized, quantitative time series of turbidity and organic absorption across Vietnam, Thailand, Cambodia, Laos, and China. To set up this system, the specific inherent optical properties (SIOPs) of the Mekong river system were determined through three separate field campaigns, laboratory analysis, and subsequent optical closure calculations. Following this, a range of satellite data types was tested using the derived Mekong-specific inherent optical properties, including Moderate Resolution Imaging Spectroradiometer (MODIS) 500 m data, Landsat ETM, Medium Resolution Imaging Spectrometer (MERIS), Satellite Pour l’Observation de la Terre (SPOT) 5, RapidEye, Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and QuickBird. The satellite-based turbidity estimates were coincident with available field data, and comparisons showed them to be in good agreement. Overall, the derived SIOPs were suitable for water-quality monitoring of the Mekong, and the MODIS, MERIS, Landsat, and RapidEye sensors were found to be the most radiometrically stable and thereby suitable for ongoing operational processing. The implemented system delivers consistent results across the different satellite sensors and over time, but is limited to where the spatial resolution of the sensor is still able to resolve the river width. The system is currently applicable for the entire Mekong river system, both for near-real-time monitoring and for analysis of historical data archive.
International Journal of Remote Sensing 04/2014; 35(8):2910-2926. · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Remote sensing has recently become a powerful tool for water quality
monitoring. Satellite-borne remote sensing information about water
quality indicators of inland water bodies has limited availability. Due
to cloudy weather or satellite instrument unavailability, time periods
without remote sensing scenes may vary from several hours to several
weeks. This is often unacceptable for operational end users. To overcome
this problem we propose an idea of assimilating satellite observations
into hydrodynamic model. In our study, we use MODIS-retrieved total
suspended matter (TSM) distribution across the lake, processed with the
Modular Inversion and Processing System (MIP). This scalar value is a
vertically integrated quantity and has to be converted to information
about TSM distribution in modeled water column. Besides TSM
concentration, also optical penetration depth (z90) can be derived from
MODIS satellite images. This quantity sets the lower integration
boundary for integrated TSM concentration from the whole water column.
Based on field studies with CTD profiler, satellite borne integrated TSM
and z90, we reconstruct a TSM profile structure. Reconstructed TSM
profiles are systematically (as far as MODIS acquisition is possible)
assimilated to hydrodynamic model. Assimilation is based on weighted
average between modeled (from Delft3d) and reconstructed (from satellite
observation) TSM profiles. Averaging weights come from pixel quality
information which is retrieved from satellite image during atmospheric
correction. As a study site, Lake Constance has been chosen. Thanks to
its large dimensions, it was possible to monitor it using the Moderate
Resolution Imaging Spectroradiometer (MODIS). Another advantage of this
study site is that in spring Lake Constance experiences also the mixing
of inflowing, highly turbid, cold Alpine Rhine water and transparent
warmer lake water. This phenomenon is highly related to hydrodynamic
(wind induced and density-driven) currents and can be monitored with
satellite-borne remote sensing. For hydrodynamic modeling, a three
dimensional Reynolds averaged Navier-Stokes hydrodynamic model (Delft3D)
was used. Inflowing glacier particles were assumed to be a passive
tracer, transported by advection according to simulated water currents.
Despite strong physical background hydrodynamic models still encounter
problems with results quality. Together with data from boundary
conditions (ex. wind shear stress, sun heat flux), models assimilate
also errors and uncertainties which make model results unreliable for
longer prediction time. This idea of data fusion from remote sensing and
hydrodynamic modeling leads to more reliable hydrodynamic transport
model results and more frequent data availability (in compare to pure
remote sensing). This research shows new possibilities in overcoming
hydrodynamic transport model uncertainty constraints and new application
field for remote sensing water quality products.
[Show abstract][Hide abstract] ABSTRACT: The construction of dams alters the flow regime and suspended sediment
dynamics of a river essentially. This is also the case in the Lancang,
the Chinese part of the Mekong river. The impact of the cascade of dams
has been reported in a number of papers, but because the actual measured
data are not accessible after the closure of the first dam in the early
1990s, these analysis are either based on the first gauging station
outside China only, or just provides aggregated numbers over long time
periods. In order to fill this knowledge and data gap, a long time
series of Landsat images of the Lancang was used to determine the
nephelometric turbidity, which in turn is closely correlated to the
suspended sediments. Turbidity is determined by the backward scattering
of light between 450 to 800nm wave length. The Landsat scenes provided
7-10 images per year allowing for a low but continuous temporal coverage
of the river reach upstream of the Dachaoshan and Xiaowan dam. This data
collection and analysis of this kind is the first publicly available for
this part of the river. From these images the turbidity, resp. the
suspended sediment load was derived along the covered river reach. The
temporal analysis the suspended sediment loads showed the impact of the
dams in terms of reduction of the mean sediment load as well as the
variability within the time spans between dam closures. Particularly the
closure of the huge Xiaowan dam in 2010 caused a dramatic decline both
before and after the dam.
[Show abstract][Hide abstract] ABSTRACT: Research, monitoring and management of large marine protected areas require detailed and up-to-date habitat maps. Ningaloo Marine Park (including the Muiron Islands) in north-western Australia (stretching across three degrees of latitude) was mapped to 20 m depth using HyMap airborne hyperspectral imagery (125 bands) at 3.5 m resolution across the 762 km(2) of reef environment between the shoreline and reef slope. The imagery was corrected for atmospheric, air-water interface and water column influences to retrieve bottom reflectance and bathymetry using the physics-based Modular Inversion and Processing System. Using field-validated, image-derived spectra from a representative range of cover types, the classification combined a semi-automated, pixel-based approach with fuzzy logic and derivative techniques. Five thematic classification levels for benthic cover (with probability maps) were generated with varying degrees of detail, ranging from a basic one with three classes (biotic, abiotic and mixed) to the most detailed with 46 classes. The latter consisted of all abiotic and biotic seabed components and hard coral growth forms in dominant or mixed states. The overall accuracy of mapping for the most detailed maps was 70% for the highest classification level. Macro-algal communities formed most of the benthic cover, while hard and soft corals represented only about 7% of the mapped area (58.6 km(2)). Dense tabulate coral was the largest coral mosaic type (37% of all corals) and the rest of the corals were a mix of tabulate, digitate, massive and soft corals. Our results show that for this shallow, fringing reef environment situated in the arid tropics, hyperspectral remote sensing techniques can offer an efficient and cost-effective approach to mapping and monitoring reef habitats over large, remote and inaccessible areas.
PLoS ONE 01/2013; 8(7):e70105. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We applied remote sensing techniques using WorldView-2 images with high spatial resolution and field verification to map the bathymetry and benthic habitats of the Puerto Morelos Reef National Park in the Mexican Caribbean. These images were processed using the standardized physics-based data processing of EOMAP´s Modular Inversion and Processing System (MIP). To generate a detailed benthic habitat map we developed a two level-classification scheme based on biological and geomorphologic characteristics. These images showed high effectiveness for mapping benthic habitat. Further improvements will emphasize and focus on the selection of regional specific main spectral components and the automation of the radiometric fine tuning. The main contribution is the generation of a detailed benthic habitat map representing functional classification by combining both maps. These studies serve for the management of marine areas in Mexico and could be extended to the entire Mesoamerican Reef System.
Geoscience and Remote Sensing Symposium (IGARSS), München; 07/2012
[Show abstract][Hide abstract] ABSTRACT: A method to obtain underwater topography for coastal areas using state-of-the-art remote sensing data and techniques worldwide is presented. The data from the new Synthetic Aperture Radar (SAR) satellite TerraSAR-X with high resolution up to 1 m are used to render the ocean waves. As bathymetry is reflected by long swell wave refraction governed by underwater structures in shallow areas, it can be derived using the dispersion relation from observed swell properties. To complete the bathymetric maps, optical satellite data of the QuickBird satellite are fused to map extreme shallow waters, e.g., in near-coast areas. The algorithms for bathymetry estimation from optical and SAR data are combined and integrated in order to cover different depth domains. Both techniques make use of different physical phenomena and mathematical treatment. The optical methods based on sunlight reflection analysis provide depths in shallow water up to 20 m in preferably calm weather conditions. The depth estimation from SAR is based on the observation of long waves and covers the areas between about 70- and 10-m water depths depending on sea state and acquisition quality. The depths in the range of 20 m up to 10 m represent the domain where the synergy of data from both sources arises. Thus, the results derived from SAR and optical sensors complement each other. In this study, a bathymetry map near Rottnest Island, Australia, is derived. QuickBird satellite optical data and radar data from TerraSAR-X have been used. The depths estimated are aligned on two different grids. The first one is a uniform rectangular mesh with a horizontal resolution of 150 m, which corresponds to an average swell wavelength observed in the 10 × 10-km SAR image acquired. The second mesh has a resolution of 150 m for depths up to 20 m (deeper domain covered by SAR-based technique) and 2.4 m resolution for the shallow domain imaged by an optical sensor. This new technique provides a platform for mapping of coastal bathymetry over a broad area on a scale that is relevant to marine planners, managers, and offshore industry.
[Show abstract][Hide abstract] ABSTRACT: Multispectral satellite data (WordView-2, IKONOS, QuickBird) are used to map bathymetry and spectral sea floor classes in a range of coastal areas. The standardized physics-based data processing integrates MODIS satellite data for the radiometric intercalibration and estimates of turbidity. This process includes corrections for sunglitter, the adjacency and the atmospheric effect. The water depth is calculated iteratively in combination with the spectral unmixing of the respective bottom reflectance on base of the subsurface reflectance. The final step of the processing classifies the bottom reflectance due to the spectral signature of different bottom types and biota using a specific cluster and classification approach. The comparison with in situ data at different sites worldwide proves the approach, but also emphasizes the necessity of radiometric well calibrated satellite data.
[Show abstract][Hide abstract] ABSTRACT: Physics-based remote sensing in littoral environments for ecological monitoring and assessment is a challenging task that
depends on adequate atmospheric conditions during data acquisition, sensor capabilities and correction of signal disturbances
associated with water surface and water column. Airborne hyper-spectral scanners offer higher potential than satellite sensors
for wetland monitoring and assessment. However, application in remote areas is often limited by national restrictions, time
and high costs compared to satellite data. In this study, we tested the potential of the commercial, high-resolution multi-spectral
satellite QuickBird for monitoring littoral zones of Lake Sevan (Armenia). We present a classification procedure that uses
a physics-based image processing system (MIP) and GIS tools for calculating spatial metrics. We focused on classification
of littoral sediment coverage over three consecutive years (2006–2008) to document changes in vegetation structure associated
with a rise in water levels. We describe a spectral unmixing algorithm for basic classification and a supervised algorithm
for mapping vegetation types. Atmospheric aerosol retrieval, lake-specific parameterisation and validation of classifications
were supported by underwater spectral measurements in the respective seasons. Results revealed accurate classification of
submersed aquatic vegetation and sediment structures in the littoral zone, documenting spatial vegetation dynamics induced
by water level fluctuations and inter-annual variations in phytoplankton blooms. The data prove the cost-effective applicability
of satellite remote-sensing approaches for high-resolution mapping in space and time of lake littoral zones playing a major
role in lake ecosystem functioning. Such approaches could be used for monitoring wetlands anywhere in the world.
KeywordsRemote sensing-Littoral vegetation-Water level fluctuations-Spectral unmixing-Inversion-QuickBird
[Show abstract][Hide abstract] ABSTRACT: The Applied Remote Sensing Cluster at the German Aerospace Center DLR has long lasting experiences with air- and spaceborne acquisition and processing of hyperspectral image data. Jointly with the German Space Operations Center it is responsible for the establishment of the ground segment of the future German hyperspectral satellite mission EnMAP (Environmental Mapping and Analysis Program) which is planned to be launched in 2013. The primary goal of EnMAP is to quantify and analyze diagnostic parameters describing key processes on the Earth’s surface. Extensive calibration and validation activities are foreseen during the planned five years of operations to ensure high quality data products, which include radiometric, geometric and atmospheric correction. This paper focuses on the automatic processing chain, as well as the calibration and quality control activities for the generation of standard EnMAP products.
[Show abstract][Hide abstract] ABSTRACT: The German Aerospace Center DLR – namely the Applied Remote Sensing Cluster CAF and the German Space Operations Center GSOC – is responsible for the establishment of the ground segment of the future German hyperspectral satellite mission EnMAP (Environmental Mapping and Analysis Program). The Applied Remote Sensing Cluster has long lasting experiences with air- and spaceborne acquisition, processing, and analysis of hyperspectral image data. This paper mainly addresses the concept of the operational and automatic processing chain and the calibration / data quality to generate high quality data products.
[Show abstract][Hide abstract] ABSTRACT: Traditional methods for aerosol retrieval and atmospheric correction of remote sensing data over water surfaces are based on the assumption of zero water reflectance in the near-infrared. Another type of approach which is becoming very popular in atmospheric correction over water is based on the simultaneous retrieval of atmospheric and water parameters through the inversion of coupled atmospheric and bio-optical water models. Both types of approaches may lead to substantial errors over optically-complex water bodies, such as case II waters, in which a wide range of temporal and spatial variations in the concentration of water constituents is expected. This causes the water reflectance in the near-infrared to be non-negligible, and that the water reflectance response under extreme values of the water constituents cannot be described by the assumed bio-optical models. As an alternative to these methods, the SCAPE-M atmospheric processor is proposed in this paper for the automatic atmospheric correction of ENVISAT/MERIS data over inland waters. A-priori assumptions on the water composition and its spectral response are avoided by SCAPE-M by calculating reflectance of close-to-land water pixels through spatial extension of atmospheric parameters derived over neighboring land pixels. This approach is supported by the results obtained from the validation of SCAPE-M over a number of European inland water validation sites which is presented in this work. MERIS-derived aerosol optical thickness, water reflectance and water pigments are compared to in-situ data acquired concurrently to MERIS images in 20 validation match-ups. SCAPE-M has also been compared to specific processors designed for the retrieval of lake water constituents from MERIS data. The performance of SCAPE-M to reproduce ground-based measurements under a range of water types and the ability of MERIS data to monitor chlorophyll-a and phycocyanin pigments using semiempirical algorithms after SCAPE-M processing are discussed. It has been found that SCAPE-M is able to provide high accurate water reflectance over turbid waters, outperforming models based on site-specific bio-optical models, although problems of SCAPE-M to cope with clear waters in some cases have also been identified.
Remote Sensing of Environment 01/2010; · 5.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Semi-analytical remote sensing applications for eutrophic waters are not applicable to oligo- and mesotrophic lakes in the perialpine area, since they are insensitive to chlorophyll concentration variations between 1 and 10 mg/m3. The neural network based Case-2-Regional algorithm for MERIS was developed to fill this gap, along with the ICOL adjacency effect correction algorithm. The algorithms are applied to a collection of 239 satellite images from 2003–2008, and the results are compared to experimental and official water quality data collected in six perialpine lakes in the same period. It is shown that remote sensing estimates can provide an adequate supplementary data source to in situ data series of the top 5 m water layer, provided that a sufficient number of matchups for a site specific maximum temporal offset are available.
Remote Sensing of Environment 01/2010; · 5.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Earth observation sensors collect valuable data of aquatic systems, which are further used for the retrieval of concentrations of water constituents such as suspended matter and phytoplankton. Different sensors deliver data with various spatial and temporal resolution ranging from 1 day to approximately a month in time and from 1 km to 3 m in space, high spatial resolution being connected with low temporal resolution and vice versa. In order to have detailed information on both spatial distribution of water constituents and their temporal variability, that is especially important for small aquatic objects like rivers and lakes, it is necessary to combine the data from several sensors. This creates certain problems as also spectral and radiometric resolutions of the sensors can be different. The use of the modular image processing system MIP for the integration of data from different sensor is advantageous as it ensures standardized product outputs for a variety of satellite sensors such as MERIS, MODIS, SPOT, IKONOS, RapidEye. The processing chain of this system is automatically adapted to the sensor parameters as well as to the region specific inherent optical properties (SIOP) of the water basin. Various worldwide applications and time series for lakes, rivers and coastal areas are demonstrated and discussed.
IEEE Geoscience and Remote Sensing Symposium, IGARSS 2009; 08/2009
[Show abstract][Hide abstract] ABSTRACT: The applicability of MERIS data for the retrieval of water constituent concentrations in oligo- to mesotrophic perialpine lakes is demonstrated by means of two different algorithms. The C2R algorithm is an easily applicable neural network processor which is bound to MERIS data. The MIP algorithm is a complex, coupled inversion program, which can be used with a variety of remote sensing sensors, but requires extensive parameterization. Both algorithms were applied with the ICOL adjacency effect correction. C2R's potential for automatic processing of large data quantities is validated in a time series study with water quality monitoring data. Individual C2R image products are then compared to MIP, which will allow for an extended comparison with new APEX imaging spectrometry data in the near future.
IEEE Geoscience and Remote Sensing Symposium, IGARSS 2009; 08/2009
[Show abstract][Hide abstract] ABSTRACT: The objective of the ESA funded project “Development of MERIS Lake Water Algorithms” (January 2007 – June 2008) was to develop and validate a plug-in module for the BEAM toolbox that allows the retrieval of water quality parameters in lake waters from MERIS imagery. For this purpose, new algorithms were developed, based on the optical properties of lakes and atmospheric aerosols from different areas of Europe. The validation campaigns were carried out in eleven lakes in Finland, Germany and Spain. A summary of the main validation results is presented.
2nd MERIS/(A)ATSR User Workshop, Frascati, Italy; 09/2008