Roy Welch

Mapping from ASTER stereo image data: DEM validation and accuracy assessment

Abstract The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on-board the National Aeronautics and Space Administrations (NASAs) Terra spacecraft provides along-track digital stereo image data at 15-m resolution. As part of ASTER digital elevation model (DEM) accuracy evaluation efforts by the US/Japan ASTER Science Team, stereo image data for four study sites around the world have been employed to validate prelaunch estimates of heighting accuracy. Automated stereocorrelation procedures were implemented using the Desktop Mapping System (DMS) software on a personal computer to derive DEMs with 30- to 150-m postings. Results indicate that a root-mean-square error (RMSE) in elevation between ±7 and ±15 m can be achieved with ASTER stereo image data of good quality. An evaluation of an ASTER DEM data product produced at the US Geological Survey (USGS) EROS Data Center (EDC) yielded an RMSE of ±8.6 m. Overall, the ability to extract elevations from ASTER stereopairs using stereocorrelation techniques meets expectations.

HYPERSPECTRAL IMAGE DATA FOR MAPPING WETLAND VEGETATION

Data acquired by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) with 224 bands, each with 0.01-μm spectral resolution and 20-meter spatial resolution, were used to produce a vegetation map for a portion of Everglades National Park, Florida, USA. The vegetation map was tested for classification accuracy with a pre-existing detailed GIS wetland vegetation database compiled by manual interpretation of 1∶40,000-scale color infrared (CIR) aerial photographs. Although the accuracy varied greatly for different classes, ranging from 40 percent for scrub red mangroves (Rhizophora mangle) to 100 percent for spike rush (Eleocharis cellulosa) prairies, the Everglades communities generally were successfully identified, averaging 66 percent correct for all classes. In addition, the hyperspectral image data proved suitable for detecting the invasive exotic species lather leaf (Colubrina asiatica) that is sometimes difficult to differentiate on aerial photographs. The findings from this study have implications for operational uses of spaceborne hyperspectral image data that are now becoming available. Practical limitations of using such image data for wetland vegetation mapping include inadequate spatial resolution, complexity of image processing procedures, and lack of stereo viewing.

ASTER as a source for topographic data in the late 1990s

Topography is a fundamental Earth characteristic that can be measured for studies of the land surface. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard the EOS-AM1 platform will acquire along-track stereo data for topographic mapping. ASTER is capable of recording 771 digital stereo pairs per day, each covering 60/spl times/60 km on the ground, at 15-m resolution, with a base-to-height ratio of 0.6. According to present plans, approximately 30 digital elevation models (DEMs), accurate to within /spl plusmn/7 to /spl plusmn/50 m (RMSE/sub z/) will be produced daily by processing facilities in Japan and the United States. The Land Processes Distributed Active Archive Center (LP-DAAC) at the United States Geological Surveys (USGSs) EROS Data Center (EDC) will emphasize the use of automated stereocorrelation procedures to produce absolute DEMs tied to ground control. During the six-year mission, ASTER has the potential to provide a coherent, digital stereo data set covering all of the Earths land surface. At minimum, ASTER DEMs will augment topographic data from other sources. Results of simulations of ASTER stereo data using existing satellite and aircraft data over validation sites in Huntsville, AL, and Iguala, Mexico, illustrate the value of high-resolution ASTER DEMs and how actual ASTER DEMs will be validated.

Photogrammetric and GIS techniques for the development of vegetation databases of mountainous areas: Great Smoky Mountains National Park

Detailed vegetation databases and associated maps of the Great Smoky Mountains National Park, a rugged, forested area of more than 2000 km 2 , were constructed to support resource management activities of the U.S. National Park Service (NPS). These detailed vegetation databases and associated maps have a terrain relief exceeding 1700 m and a continuous forest cover over 95% of the Park. The requirement to use 1:12,000- and 1:40,000-scale color infrared aerial photographs as the primary data source for mapping overstory and understory vegetation, respectively, necessitated the integration of analog photointerpretation with both digital softcopy photogrammetry and geographic information system (GIS) procedures to overcome problems associated with excessive terrain relief and a lack of ground control. Applications of the vegetation database and associated large-scale maps include assessments of vegetation patterns related to management activities and quantification of forest fire fuels.

Measurement of Ephemeral Gully Erosion

ABSTRACT THE Universal Soil Loss Equation often under-estimates erosion on agricultural fields because it does not account for the loss of soil from ephemeral gullies. However, the development of appropriate predictive methodology along with the understanding of the erosional processes are limited by the difficulty of acquiring adequate data on ephemeral gully erosion. This paper describes an aerial photogrammetric method for making accurate and repetitive field measurements of ephemeral gully erosion. Stereo aerial photographs are aquired of a field before and after gully changes caused by erosion or tillage. Data reduction of the stereopairs with photogrammetric procedures provides X, Y and Z terrain coordinates with approximate vertical measurement accuracies of ± 25 mm and contour intervals of 0.15 m. The methodology was tested on a 5.34 ha field that contained two major gullies with eroded depths approaching 0.5 m. Over nearly three years, soil volume changes in the gullies were computed to give the quantities of soil removed by erosion or filled by tillage. The distribution of the soil volume changes along the gullies portrayed the zones and quantities of deposition as well as erosion. This data base offers considerable potential for studying ephemeral gully erosion and developing predictive methodology.

GIS technologies for aquatic macrophyte studies: Modeling applications

A GIS database developed for Lake Marion, South Carolina was utilized to assess existing relationships between aquatic macrophyte distributions and environmental parameters affecting plant growth. The significance of water depth, sedimentation, nitrogen, phosphorus, top dissolved oxygen, bottom dissolved oxygen, percent light and absolute light was tested using GIS overlay techniques and the Chi Square test of independence. Specific levels of the eight parameters found to be spatially related to aquatic vegetation were then utilized to develop a provisional cartographic model describing optimum growth conditions for aquatic macrophytes. Model validation by comparing predicted vegetation with actual vegetation distributions indicated only water depth and sedimentation data layers are necessary for predicting more than 90 percent of emergent and submergent distributions. Resource managers can use this model to identify lake areas that are susceptible to excessive macrophyte growth and require special attention.

GIS technologies for aquatic macrophyte studies: I. Database development and changes in the aquatic environment

Geographic information system (GIS) and digital database technologies provide a link between landscape-scale ecological studies and resource management applications. A case study involves the development of an extensive GIS database for upper Lake Marion, South Carolina that includes macrophyte distributions for 1972–1988, bathymetry, sedimentation and water chemistry. This database was utilized to assess changes in the aquatic environment related to management practices such as herbicide applications for aquatic plant control. Although the herbicides were found to be very effective, spraying must be repeated annually to maintain open water areas clear of aquatic vegetation. Without herbicides macrophytes quickly reinvade and proceed in normal successional patterns to establish submergent and emergent aquatic plant beds. The PC-based procedures developed in this study can be utilized by local resource managers to assess the impact of management practices on the aquatic environment.

Cartographic Accuracy of LANDSAT-4 MSS And TM Image Data

Investigations of the cartographic quality of Landsat-4 MSS and TM image data in CCT-p formats have produced rectification accuracies (rmsexy values) of ± 2/3 to ± 1 data pixel for both whole and subscene areas using polynomials of the first through third degree. In order to achieve these accuracies with MSS data, 15 or more Ground Control Points (GCPs) are required, whereas with the TM data sets as few as 5-10 GCPs will suffice. Factors which limit the cartographic rectification accuracies of the Landsat-4 data include: 1) spatial resolution of the data; 2) map and digitizing errors; and 3) terrain relief. Of these factors, data resolution is the most significant, limiting the location of GCPs to about ± 0.5 pixel. Horizontal displacements due to terrain relief can be minimized by selecting GCPs at or near midrange elevations. Overall, the representative rmsexy values of ±25 and ±55 m for TM and MSS data sets are within U.S. National Map Accuracy Standards for cartographic products of 1:100 000 and 1:200 000 scale, respectively.

ASTER along-track stereo experiment: a potential source of global DEM data in the late 1990s

In addition to acquiring multispectral data, the advanced spaceborne thermal emission and reflectance radiometer (ASTER) will also acquire along-track stereo data. ASTER is capable of acquiring 771 digital stereo pairs per day, each covering 60 by 60 km on the ground, at 15 m resolution with a base/height ratio of 0.6. According to present plans, approximately 30 digital elevation models (DEMs), with 7 - 50 m accuracy (RMSExyz) will be produced daily. During the 5 year mission on the EOS AM1 platform, ASTER has the potential to provide a coherent digital stereo dataset covering the Earths land surface. At minimum, DEMs derived from these data will augment topographic data from other sources. These fundamental geophysical measurements will be a major contribution to interdisciplinary studies of the Earth as a planet.

Mapping The Earth From Space In The 1980's

Satellite programs of the 1980s such as Landsat-5, Shuttle/Spacelab and SPOT will produce a variety of image data recorded by film cameras, electro-optical sensors and synthetic aperture radars which can be used for mapping tasks. Efforts will focus on producing topographic, thematic and image maps at scales of 1:25,000 to 1:100,000. Studies to date indicate that spatial resolution and geometric fidelity are the most important factors controlling the completeness of detail and accuracy to which terrain coordinates can be derived. As most satellite systems do not currently provide both spacecraft position and attitude data to sufficient accuracies for cartographic purposes, terrain coordinates must be derived from image measurements referenced to ground control. Of the satellite systems currently planned for operation during the next two years, the Large Format Camera and Metric Camera employed on board the Shuttle will provide photographs with resolution and geometric characteristics compatible with map products at 1:50,000 scale. SPOT, which will produce both 10m panchromatic and 20m multispectral data in stereo formats, will provide digital data of the Earth suitable for cartographic applications.