Anisotropic Reflectance Correction Of SPOT-3 HRV

The problem of anisotropic reflectance in mountainous terrain is well known. It was required to determine the efficacy of anisotropic reflectance correction (ARC) of imagery acquired over the western Himalaya. The Minnaert correction procedure was evaluated using a single Minnaert constant (k), locally computed ks and land cover-computed ks. Findings illustrate the need for computing ks, such that anisotropic reflectance caused by topography and land cover is accounted for. This resulted in a significant reduction in the topographic effect. The results indicate that land cover-computed k values can be used effectively for anisotropic reflectance correction

Techniques For GIS Modeling Of Coastal Dunes

Coastal dunes present a unique problem to coastal scientists because of the dynamic nature of most coastal dune systems. Coastal dunes can change shape quickly and frequently due to storm-generated winds and waves. Prevailing winds can transport significant amounts of sand throughout the dune system. Topographic and volumetric changes in a 150×40 m site on the Outer Banks of North Carolina were assessed through a series of monthly field surveys conducted over a 1-year period from May 1997 to May 1998. This paper discusses the Geographic Information System (GIS) methodology used for data acquisition and analysis and presents one methodology developed to measure 3-D dune morphodynamics using a 2-D and 3-D GIS. It serves as a guide for other coastal researchers who may have limited surveying or GIS experience. Issues concerning sampling routine, data density and grid cell size are discussed. The methodology followed results in the production of a grid of interpolated elevation values that can be represented in a variety of ways, including as topographic maps, digital elevation models (DEM) or two-dimensional cross-sections of the dune system. The grid from the May 1998 survey is subtracted from the May 1997 grid to obtain elevation change information that in turn can be represented graphically. The results of the analysis show that volumetric change over the 1-year period was dominated by erosion along the seaward face of the dune. The monthly surveys show that this erosion was the result of two northeasters in January and February 1998. The loss of volume is partially compensated for by accumulation to the rear of the foredune ridge, primarily in locations where blowouts facilitate aeolian transport of sediment from the beach. The implication is that the dune system is eroding rapidly due to storm activity. It also suggests that there is a mechanism for offsetting some of the volumetric loss through aeolian transport into the dune system

Spatial Characterization, Resolution, And Volumetric Change Of Coastal Dunes Using Airborne LIDAR: Cape Hatteras, North Carolina

The technological advancement in topographic mapping known as airborne Light Detection and Ranging (LIDAR) allows researchers to gather highly accurate and densely sampled coastal elevation data at a rapid rate. The problem is to determine the optimal resolutions at which to represent coastal dunes for volumetric change analysis. This study uses digital elevation models (DEM) generated from LIDAR data and spatial statistics to better understand dune characterization at a series of spatial resolutions. The LIDAR data were collected jointly by the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the U.S. Geological Survey (USGS). DEMs of two study sites (100×200 m) located in Cape Hatteras National Seashore, North Carolina were generated using a raster-based geographic information system (GIS). Changes in the dune volume were calculated for a 1-year period of time (Fall 1996–1997) at grid cell resolutions ranging from 1×1 to 20×20 m. Directional statistics algorithms were used to calculate local variance and characterize topographic complexity. Data processing was described in detail in order to provide an introduction to working with LIDAR data in a GIS. Results from these study sites indicated that a 1–2 m resolution provided the most reliable representation of coastal dunes on Cape Hatteras and most accurate volumetric change measurements. Results may vary at other sites and at different spatial extents, but the methods developed here can be applied to other locations to determine the optimum resolutions at which to represent and characterize topography using common GIS and database software

An Efficient Method For Mapping Flood Extent In A Coastal Floodplain Using Landsat TM And DEM Data

An efficient and economical method for mapping flooding extent in a coastal floodplain is described. This method was based on the reflectance features of water versus non-water targets on a pair of Landsat 7 Thematic Mapper (TM) images ( before and during the flood event), as well as modelling inundation using Digital Elevation Model (DEM) data. Using limited ground observation, most flooded and non-flooded areas derived from this analysis were verified. Utilizingonly TM data, the total flooded areas in Pitt County, North Carolina on 30 September 1999 was 237.9 km2 or 14.0% of the total county area. This number could be low due to the underestimation of the flooded areas beneath dense vegetation canopies. To further investigate this underestimation, a subset of the area covering the four central topographic quadrangles, the Greenville area, in Pitt County was selected. Through addition of the DEM data into the flood mapping analysis of the Greenville area revealed that the total flooded area was 98.6 km2 (out of a study area of 593.9 km2 ) or 16.5%. In the Greenville study area, the three landuse and landcover categories most aVected by the flood were bottomland forest/hardwood swamps (32.7 km2 ), southern yellow pine ( 28.8 km2 ), and cultivated land (19.1 km2 ). Their total flooded areas were 80.6 km2 or 81.7% of the total flooded area within this study area. The DEM data helped greatly in identifying the flooding that occurred underneath forest canopies, especially within bottomland forest and hardwood swamps. The method was reliable and could be applied quickly in other coastal floodplain regions using data that are relatively easy to obtain and analyse, and at a reasonable cost. This method should also work well in areas of large spatial extent where topography is relative flat

Land Cover Classification Using Landsat TM Imagery In The Tropical Highlands: The Influence Of Anisotropic Reflectance

Despite the tremendous attention given to conservation projects in the Neotropics, few published studies have documented remote sensing studies in tropical highland areas. Even fewer publications have addressed the use of topographic normalization methods in these regions. This article discusses the influence of anisotropic reflectance patterns on land cover classification for two study areas characterized by very rugged terrain and high relief. Landsat Thematic Mapper subscenes for sites in both Costa Rica and Ecuador were corrected using both Lambertian and non-Lambertian models. While use of the Lambertian model proved inappropriate for these mountainous areas, application of the non-Lambertian model enhanced classification accuracies

Remote Sensing And Geomorphometry For Studying Relief Production In High Mountains

Mountain topography is the result of highly scale-dependent interactions involving climatic, tectonic, and surface processes. No complete understanding of the geodynamics of mountain building and topographic evolution yet exists, although numerous conceptual and physical models indicate that surficial erosion plays a significant role. Mapping and assessing landforms and erosion in mountain environments is essential in order to understand landscape denudation and complex feedback mechanisms. This requires the development and evaluation of new approaches in remote sensing and geomorphometry. The research herein evaluates the problem of topographic normalization of satellite imagery and demonstrates the use of terrain analysis using a digital elevation model (DEM) to evaluate the relief structure of the landscape in the western Himalaya. We specifically evaluated the Cosine-correction and Minnaert-correction methods to reduce spectral variation in imagery caused by the topography. Semivariogram analyses of the topography were used to examine the relationships between relief and surface processes. Remote-sensing results indicate that the Minnaert-correction method can be used to reduce the “topographic effect” in satellite imagery for mapping, although extreme radiance values are the result of not accounting for the diffuse-skylight and adjacent-terrain irradiance. Geomorphometry results indicate that river incision and glaciation can generate extreme relief, although the greatest mesoscale relief is produced by glaciation at high altitudes. At intermediate altitudes, warm-based glaciation was found to decrease relief. Our results indicate that glaciation can have a differential influence on the relief structure of the landscape. Collectively, our results indicate that scale-dependent analysis of the topography is required to address radiation transfer issues and the polygenetic nature of landscape denudation and relief production

Modeling Flooding Extent Due To Hurricane Floyd In The Coastal Plains Of North Carolina

In this article two modeling approaches were developed based on the use of US Geological Survey digital elevation model (DEM) data. These models were utilized to delineate the extent of flooding induced by precipitation from Hurricane Floyd in a portion of Pitt County, North Carolina. The patterns of flood extent derived from the two models were compared to the extent of flooding indicated on a digital aerial photograph taken two days after peak flood levels had been reached. In addition, floodplain boundaries based on Federal Emergency Management Agency Q3 maps were compared to the extent of flooding on the aerial photo. Actual emergency response operations undertaken through the Pitt County Emergency Operations Center during the flood event are described, and are used to provide a context for evaluating the potential utility of these models. The flood extents produced by the modeling methods performed well at representing the actual extent of the flooding

Flood Modeling In The Coastal Plains And Mountains: Analysis Of Terrain Resolution

The number of flood disasters has increased worldwide in recent decades. Identifying the optimal resolution or scale at which to represent digital terrain models (DTMs) is critical in order to improve our ability to accurately and efficiently model floods. Few studies have attempted to compare flood modeling results using different resolutions of DTMs in divergent environments. In this study flooding on the Tar River in the coastal plains and the Watauga River in the mountains of North Carolina were modeled using hydrologic information obtained following Hurricanes Floyd and Ivan. The effectiveness of DTMs derived from light detection and ranging and United States Geological Survey elevation data at commonly available resolutions in North Carolina were assessed. A quantitative diagnostic method based on measuring the distance flooded along transects was applied for evaluating the horizontal extent and internal pattern of flooding. The use of additional diagnostic metrics (area, volume, and shape) along with a visual graphic assessment enhanced the evaluation of flood modeling results. The extent and internal pattern of flooding in the low-relief coastal plains was found to be especially sensitive to the representation of terrain, and in the mountains 30 X 30-m data regardless of source were found to be dramatically unsuitable for flood modeling

Flood Modeling Using A Synthesis Of Multi-Platform LiDAR Data

This study examined the utility of a high resolution ground-based (mobile and terrestrial) Light Detection and Ranging (LiDAR) dataset (0.2 m point-spacing) supplemented with a coarser resolution airborne LiDAR dataset (5 m point-spacing) for use in a flood inundation analysis. The techniques for combining multi-platform LiDAR data into a composite dataset in the form of a triangulated irregular network (TIN) are described, and quantitative comparisons were made to a TIN generated solely from the airborne LiDAR dataset. For example, a maximum land surface elevation difference of 1.677 m and a mean difference of 0.178 m were calculated between the datasets based on sample points. Utilizing the composite and airborne LiDAR-derived TINs, a flood inundation comparison was completed using a one-dimensional steady flow hydraulic modeling analysis. Quantitative comparisons of the water surface profiles and depth grids indicated an underestimation of flooding extent, volume, and maximum flood height using the airborne LiDAR data alone. A 35% increase in maximum flood height was observed using the composite LiDAR dataset. In addition, the extents of the water surface profiles generated from the two datasets were found to be statistically significantly different. The urban and mountainous characteristics of the study area as well as the density (file size) of the high resolution ground based LiDAR data presented both opportunities and challenges for flood modeling analyses