Keqi Zhang

Florida International University | FIU · Department of Earth and Environment

Mangroves have been proven to be effective in storm surge attenuation but it remains an important challenge to accurately quantify such bio-shielding effects using numerical simulations, as it is very difficult to comprehensively represent the ecological characteristics of mangroves at both large and small scales. In this study, a numerical method...

Low elevation outliers (LEOs) in TanDEM-X (TDX) digital elevation models (DEMs) have a great effect on the accuracy of digital terrain models (DTMs) generated by filtering DEM data. A novel method, combining local elevation histograms and adaptive triangulated irregular network (HATIN), was developed to detect LEOs in TDX DEMs. The performance of H...

This study develops a method to identify the depth of closure using airborne laser bathymetric data, and compares the measured depth of closure to calculated depth of closures and subaqueous geomorphic units. Airborne laser data sets were collected before and after the 2004 hurricane season along 100 km of beaches in Palm Beach, Broward, and Miami-...

Mangrove migration, or transgression in response to global climatic changes or sea-level rise, is a slow process; to capture it, understanding both the present distribution of mangroves at individual patch (single- or clumped trees) scale, and their rates of change are essential. In this study, a new method was developed to delineate individual pat...

The TanDEM-X (TDX) mission launched by the German Aerospace Center delivers unprecedented global coverage of a high-quality digital elevation model (DEM) with a pixel spacing of 12 m. To examine the relationships of terrain, vegetation, and building elevations with hydrologic, geologic, geomorphologic, or ecologic factors, quantification of TDX DEM...

The geographic area that the Joint Airborne LiDAR Bathymetry Technical Center of Expertise (JALBTCX) covers with their Light Detection and Ranging (LiDAR) program allows for researchers to quantify coastal metrics on national, regional and local scales. As these studies progressed, it has become apparent that software needs to be developed to quant...

This study evaluated the impact of human modifications and natural variations (e.g., seasonal riverine fluxes, plant growth, and estuarine environments) on the short-term morphological changes in estuarine tidal flats. Central to the study was an embankment, constructed in 2014, which changed the path of a tidal flat evolution in the Yangtze Estuar...

Quantification of tidal flat morphological changes at varying timescales is critical from a management point of view. High-resolution tidal flat morphology data, including those for mudflats and salt-marshes, are rare due to monitoring difficulty by traditional methods. Recent advances in Terrestrial Laser Scanner (TLS) technology allow rapid acqui...

Hurricanes Frances, Jeanne, and Wilma passed over Lake Okeechobee, Florida, in September 2004 and October 2005, respectively. Strong winds caused a large surface seiche on the lake during all three storms. These storms resulted in erosion damage to the Herbert Hoover Dike (HHD) on Lake Okeechobee. In this paper, we use the Fully Adaptive Storm Tide...

Kelly et al. (Coast Eng J 57(4):1–30, 2015) present a finite volume dynamic adaptive mesh model based on Osher’s approximate Riemann solver for the prediction of storm surges over complex landscapes. Here, the model described in that paper is extended to use distributed memory parallel block tree-based mesh refinement via the PARAMESH library. The...

Knowledge of the spatial and temporal changes caused by episodic disturbances and seasonal variability is essential for understanding the dynamics of mangrove forests at the landscape scale, and for building a baseline that allows detection of the effects of future environmental change. In combination with LiDAR data, we calculated four vegetation...

A numerical model for the prediction of storm surges over complex landscapes is assembled using state-of-the-art techniques. The model is based on the full nonlinear depth-averaged long wave equations solved via an explicit finite volume scheme. The interfacial fluxes are computed from slope limited reconstructions of the state variables using Oshe...

The snake algorithm has been proposed to solve many remote sensing and computer vision problems such as object segmentation, surface reconstruction, and object tracking. This paper introduces a framework for 3-D building model construction from LIDAR data based on the snake algorithm. It consists of nonterrain object identification, building and tr...

High quality DEM (Digital Elevation Model) is indispensable for a smart city nowadays. A large quantity of useful spatial information can be extracted from the big data acquired by surveying, imaging, and even mobile device with GPS system. This information is critical to many applications such as urban management, emergency event planning, and soc...

This paper presents a Graphical User Interface (GUI) system to process huge volume geospatial data acquired from LIDAR survey. This GUI system provides friendly user interface to display, edit and process LIDAR data. It also offers useful geospatial tool kits to process area of interest from a big data set. The processing results would be used for...

LIDAR (Light Detection and Ranging) is a widely used technology to measure terrain properties and topographic mapping nowadays. Many filtering methods have been developed to process the geospatial data generated by LIDAR to generate bare earth digital terrain models. Among these methods, mathematical morphological filtering is a very effective and...

The sensitivity of the mangrove effect on reducing storm surge flooding to hurricane characteristics is investigated by using the numerical model Coastal and Estuarine Storm Tide (CEST). First, the attenuation of storm surge by mangroves is incorporated into the model by updating Manning’s coefficient based on the National Land Cover Dataset (NLCD)...

The operational forecast demands and constraints of the National Hurricane Center require that a storm surge model in research mode be tested against a benchmark model such as Sea, Lake, and Overland Surges from Hurricanes (SLOSH) for accuracy, computation time, and numerical stability before the model is used for operational forecasts. Additionall...

Two linear methods, including the simple linear addition and linear addition by expansion, and numerical simulations were employed to estimate storm surges and associated flooding caused by Hurricane Andrew for scenarios of sea level rise (SLR) from 0.15 m to 1.05 m with an interval of 0.15 m. The interaction between storm surge and SLR is almost l...

Oceanic responses to a hypothetical landfalling tropical cyclone (TC) are studied by using a coupled atmosphere-wave-ocean modeling system (CAWOMS). A set of experiments are conducted to compare the effects of atmosphere-wave-ocean interaction on ocean responses in coastal and deep waters. The results show that in a three-way coupled atmosphere-wav...

In this chapter, we propose a system which integrates storm surge projection, meteorological, topographical, and road data to simulate storm surge conditions. The motivation behind the system is to serve local governments seeking to overcome difficulties in persuading residents to adhere to evacuation notices. The storm surge simulation system intr...

Background/Question/Methods Key Biscayne is the southernmost of the barrier beaches along the coast of the southeastern U. S. Prior to the 20th Century, vegetation on the island consisted primarily of beach vegetation on the eastern shore, backed by oak-palmetto scrub on the dunes, and an interdigitating mangrove forest that extended to Biscayne...

Background/Question/Methods The Miami-Dade urban region is characterized by a unique and paradoxical set of conditions and forces: a global commerce center, where assets are vulnerable to catastrophic coastal disasters; an affluent city with among the highest rates of poverty in the nation; a de-vegetated city situated between and dependent upon...

The potential impacts of sea level rise (SLR) on 95% of the land areas of the Florida Keys were estimated through analysis of a digital elevation model (DEM) derived from airborne light detection and ranging (LiDAR) measurements in a geographic information system. The topographic detail of the LiDAR DEM allowed projections of land, population, and...

A 1.5 m sea level rise by 2100 will cause calamitous inundation to Miami-Dade and Broward Counties and the Everglades in South Florida. Inundation processes are non-linear: inundation is gradual before reaching a tipping point, and speeds up rapidly afterwards due to the regional topography. Accelerated sea level rise will cause the tipping point t...

By analyzing a digital elevation model (DEM) derived from airborne light detection and ranging (LIDAR) data and airborne height finder measurements, this study demonstrates that a 1.5m sea-level rise by 2100 would cause inundation of large areas of Miami-Dade County, southern Broward County, and Everglades National Park. Inundation processes are no...

Barrier islands, the dominant geomorphic features along the U.S. Atlantic and Gulf Coasts, are a favorite place for living and visiting. Unfortunately, barrier islands are vulnerable to storm-surge flooding and erosion because of low elevations and the movement of sand by waves and tides. In order to estimate the impacts of surge flooding, sea-leve...

The effectiveness of simulating surge inundation using the Eulerian–Lagrangian circulation (ELCIRC) model over multi-scale unstructured grids was examined in this study. The large domain model grid encompasses the western North Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea to appropriately account for remote and resonance effects during...

The distribution of mangrove biomass and forest structure along Shark River estuary in the Florida Coastal Everglades (FCE) has been correlated with elevated total phosphorus concentration in soils thought to be associated with storm events. The passage of Hurricane Wilma across Shark River estuary in 2005 allowed us to quantify sediment deposition...

The rise of offshore water caused by the high winds of a low pressure weather system, or storm surge, is a hurricane's greatest threat to human life. As weather forecasters struggle to enable coastal residents to make timely evacuation decisions, the need arises for more visually compelling and interactive storm surge visualization tools. This pape...

The authors summarize the main findings of the Florida Coastal Everglades Long-Term Ecological Research (FCE-LTER) program in the EMER, within the context of the Comprehensive Everglades Restoration Plan (CERP), to understand how regional processes, mediated by water flow, control population and ecosystem dynamics across the EMER landscape. Tree ca...

Sea-level rise presents an imminent threat to freshwater-dependent ecosystems on small oceanic islands, which often harbor rare and endemic taxa. Conservation of these assemblages is complicated by feedbacks between sea level and recurring pulse disturbances (eg hurricanes, fire). Once sea level reaches a critical level, the transition from a lands...

A framework which includes six major components has been developed to reconstruct 3D building models from airborne LiDAR measurements. The application of the framework to both commercial and adjacent residential areas shows that the proposed methods identified building patches well, and reconstructed 3D building models effectively. The entire proce...

Nutrient loading and eutrophication in coastal waters are the causes of water quality degradation and loss of marine biota, which has led to ecological imbalance. Understanding and modeling the level of eutrophication as a function of environmental parameters can be beneficial to coastal ecosystem management. The limitation of deterministic and emp...

This paper presents a 3D traffic animation system that provides features of vehicle interaction and storm surge response to emulate realistic scenarios in a hurricane affected area. The proposed system constructs road objects based on a series of line segments. Vehicles on the roads are animated by keeping them coherent with the direction of the ro...

This study develops a method to identify the depth of closure using airborne laser bathymetric data, and compares the measured depth of closure to calculated depth of closures and subaqueous geomorphic units. Airborne laser data sets were collected before and after the 2004 hurricane season along 100 km of beaches in Palm Beach, Broward, and Miami-...

Mangrove forests change frequently due to disturbances from tropical storms, frost, lightning, and insects. It has been suggested that the death and regeneration of trees in small gaps due to lightning may play a critical role in mangrove forest turnover; however, the large-scale quantification of spatial pattern and areas of gaps is lacking for in...

Airborne light detection and ranging (LIDAR) measurements derived before and after Hurricanes Katrina and Wilma (2005) were used to quantify the impact of hurricanes and lightning strikes on the mangrove forest at two sites in Everglades National Park (ENP). Analysis of LIDAR measurements covering 61 and 68 ha areas of mangrove forest at the Shark...

The Coastal and Estuarine Storm Tide (CEST) model for the boundary-fitted curvilinear grid has been developed recently to simulate a hurricane-induced storm surge. A new wetting-drying algorithm was based on accumulated volume and was created for simulating overland flooding. To evaluate the capability of the CEST model, it was compared with the we...

This paper illustrates branch breaking and flying effect animation for trees in our 3D interactive visualization system for hurricanes and storm surge flooding. The tree branch breaking and flying effect animation extends our current tree animation framework by estimating the destination quadrant, direction (angle) and traveling speed with which a...

Depth of closure (DOC) is an important concept in coastal engineering that defines the seaward limit of significant net sediment transport along a wave-dominated sandy beach profile. Few surveys measured the DOC over large areas because traditional methods for measuring DOC are time consuming and cost prohibitive. With a dramatic increase in airbor...

Airborne LIDAR technology allows accurate and inexpensive measurements of topography, vegetation canopy heights, and buildings over large areas. In order to provide researchers high quality data, NSF has created the National Center for Airborne Laser Mapping (NCALM) to collect, archive, and distribute the LIDAR data. However, the LIDAR systems coll...

This study develops a method to identify the depth of closure using airborne laser bathymetric data, and compares the measured depth of closure with estimated depth of closures. Airborne laser data sets were collected before and after the 2004 hurricane season in southeast Florida. Estimated depth of closures in terms of wave data is compatible to...

This study used airborne laser data to investigate spatial variations in shoreline migration, beach width, subaerial volume, and subaqueous volume change due to a hurricane event. Five separate airborne laser data sets of Panama City, FL area beaches were collected during a seven-month period before and after landfall of Hurricane Ivan. Contour sho...

SHEN, J.; ZHANG, K.; XIAO, C., and GONG, W., 2006. Improved prediction of storm surge inundation with a high-resolution unstructured grid model. Journal of Coastal Research, 22(6), 1309–1319. West Palm Beach (Florida), ISSN 0749-0208. Accuracy of predicting storm surge inundation depends on the model grid resolution. The spatial resolutions of many...

This paper presents a framework that applies a series of algorithms to automatically extract building footprints from airborne light detection and ranging (LIDAR) measurements. In the proposed framework, the ground and nonground LIDAR measurements are first separated using a progressive morphological filter. Then, building measurements are identifi...

In this paper we describe a methodology to map mangrove forests in 3D in the Caribbean region. We used shuttle radar topography mission (SRTM) elevation, lidar and field data to estimate mangrove mean tree height at the landscape scale. This paper emphasizes two regions which are undergoing ecosystem restoration activities: The Everglades National...

Remote sensing technologies have provided valuable data for landscape modeling, vegetation mapping and comprehensive studies of ecosystems. Airborne laser mapping or LIDAR (Light Detection and Ranging) can directly measure the three dimensional structure of plant canopies, as well as, provide accurate digital terrain models (DTM). While temperate a...

We produced a landscape scale map of mean tree height in mangrove forests in Everglades National Park (ENP) using the elevation data from the Shuttle Radar Topography Mission (SRTM). The SRTM data was calibrated using airborne lidar data and a high resolution USGS digital elevation model (DEM). The resulting mangrove height map has a mean tree heig...

Three-dimensional computer visualization and animation can provide a substitute for coastal residents', lack of personal experience with hurricane-surge flooding. Tremendous progress has been made in D animation in the last decade, which movies such as Perfect Storm and The Day After Tomorrow have demonstrated. However, the D visualization and anim...

Hurricanes are a major source for erosion and damage along the southeastern US coastline. This study uses airborne LIDAR data to quantify shoreline change due to Hurricane Ivan. Hurricane Ivan made landfall on the Alabama gulf coast in September, 2004 with maximum sustained winds of 58 m/s. Five separate LIDAR data sets of barrier beaches situated...

This paper describes an implementation of vertex weighting for real-time animation of 3D trees as a result of wind force and direction. This method improves over similar techniques because it incorporates individual branch animation on 3D models, whereas previous works perform animations on the model as a whole or use planar billboards to visualize...

This paper compares three methods for removing non-ground measurements from airborne laser scanning data. These methods, including the elevation threshold with expanding window (ETEW), maximum local slope (MLS), and progressive morphological (PM) filters, analyze data points based on variations of local slope, and elevation. Low and high-relief dat...

Quantitative data on beach changes caused by coastal storms is critical to the understanding of coastal morphodynamics and mitigation of coastal erosion hazards. Recent advances in airborne LIDAR technology allow large-scale mapping of beach erosion, dune scarping, and overwash deposition with incredible detail. By comparing 40 km of beaches along...

An accretion/erosion wave is a local irregularity in beach form that moves along the shore in the direction of net littoral drift. The initial irregularity may be caused by a wide variety of events such as the bulge from an ephemeral stream delta, the material from the collapse of a sea cliff, erosion or accretion associated with convergence and di...

ISSN 0749-0208. This paper examines the feasibility of using LIDAR surveys to update existing historical shoreline data sets by com-paring contour shorelines and the high water line (HWL) at eight study locations in North and South Carolina. The analysis was based on airborne LIDAR topography and orthoimagery collected simultaneously during June 20...

One of the most certain consequences of global warming is an increase of global (eustatic) sea level. The resulting inundation from rising seas will heavily impact low-lying areas; at least 100 million persons live within one meter of mean sea level and are at increased risk in the coming decades. The very existence of some island states and deltai...

Recent advances in airborne light detection and ranging (LIDAR) technology allow rapid and inexpensive measurements of topography over large areas. This technology is becoming a primary method for generating high-resolution digital terrain models (DTMs) that are essential to numerous applications such as flood modeling and landslide prediction. Air...

This paper describes an approach to develop a high performance animation environment for storm surge. The system provides the capability to simulate the storm surge effects in the physical world by (1) modeling a region using the airborne light detection and ranging (LIDAR) data, USGS orthophotos, RLG road data and photos; (2) animating the storm i...