|Cheyenne Bottoms Study Site||Digital Elevation Models||IKONOS Datasets|
|Ortho Image Draping and Flythrough||Conclusion|
The study area contains part of the Cheyenne Bottoms wetland and preserve located in Barton County Kansas north and east of Great Bend.
Cheyenne Bottoms is an important waypoint for millions of migratory birds in this hemisphere. Part of the Bottoms is designated the Cheyenne Bottoms Preserve The preserve is located in a "...41,000 acre natural land sink...formed by geological forces about 65 million years ago. (Hands, 1998)" This land sink provides a convenient, bountiful and relatively safe waypoint for millions of migratory birds every year.
Considerable concern has surrounded the Bottoms in the past two decades, as dropping aquifer levels and other natural and artificial effects combine to threaten the survival of the wetlands. The use of deep wells along with human population growth and water consumption are believed to be responsible for this rapid decline in the aquifer levels. Yet the Bottoms seem to have a defense against the dropping water levels, and the "...subsurface structure of the basin isolates this pocket of ground water from the declining levels of regional water tables.(Zimmerman, 1990, pp.33)"
The Cheyenne Bottoms area is located approximately ten miles northeast of Great Bend and approximately eight miles southwest of Hoisington in Barton County, Kansas.
More information is available at the Emporia State University Cheyenne Bottoms HYSPIRE (HYper SPatial Imagery of Rural Environments) link.
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Acquisition and Processing
Digital Elevation Models (DEMs) are raster datasets (similar to thematic image data) with cell values representing local cell elevation. DEMs can be displayed and used by themselves, or they can be used to add depth or other important data to another type of dataset.
For example, using DEMs, one can mathematically determine the local slope of an area, or model the water drainage basin for an area.
In this project, DEM data was used in conjunction with data from the IKONOS satellite to produce images that display both elevation and thematic data. The DEM files used in this project were located at the State of Kansas DASC using a data availability map which indicated that DEMs were available for Barton County, KS. Once located, the four relevant files were transferred via FTP and stored on the local computer.
The DEM data were delivered compressed in zip format. After decompression, the first step in importing the DEM data was to use the IDRISI software function "DEMIDRIS" to convert the raw DEM to a format IDRISI could use.
I could now display all four DEM files as 2d graphical images, and could see that they physically matched the description found at the image location map. Of the four files, one was the northwest quarter of the scene, a second was the north east quarter, and so on. Comparing this data to the IKONOS satellite data, it could be seen that the IKONOS scenes overlapped the four DEM files. Consequently, these files needed to be converted into a single, larger DEM.
|This is the DEM image resulting from importing and running the CONCAT module with the four individual DEMs. The image is displayed autoscaled in quantiles with sixteen classes using the idris16 palette.|
Ideally, one might then use other data (such as multispectral Landsat or IKONOS data) to overlay on the DEM for analysis and comparison. However, Idrisi's ORTHO function has some limitations which become apparent when trying to overlay data from different spatial data sets. ORTHO will not function with any dataset which does not match the coordinate system, rows, and columns of the base DEM.
The solution to this problem involves resampling the DEM (the lower spatial resolution data) to match the higher spatial resolution of the IKONOS data, and then applying the WINDOW module to the image(s) to crop the larger image to match the smaller.
In this case, the DEM was larger than the IKONOS datasets. After doing simple calculations to determine the multiplication ratios necessary to arrive at the proper pixel pitch, the RESAMPLE module was run to convert the DEM to an image with far higher apparent resolution. It must be emphasized that this is false resolution! The DEM resolution (many meters) was simply divided to produce multiple cells for each previous cell. The data physically appears to be 4m resolution, but in fact is still the 30m (X,Y) resolution of the original DEM.
|After the procedures described above, the image still appears unchanged. However, the underlying data structure is now compatible with the IKONOS data introduced in the next section.|
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IKONOS is operated as a commercial satellite imaging venture by Space Imaging of Thornton, Colorado. Data was obtained from Dr. James Aber, and was originally purchased by request from Space Imaging.
The raw data is delivered as individual bands--monochrome images where intensity represents the intensity of light in a particular band width. The bands used in this project are Band 1 (blue), Band 2 (green), Band 3 (red), and Band 4 (Near IR).
|This is a simple image created with the Idrisi COMPOSIT module. Bands are Red, Green, and Blue representing nearly true colors. The image is not exactly true color to the human eye because the sensitivity of the multispectral scanners and the human eye differs for the various wavelengths of light.|
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One of the most visually appealing ways to display data is as an ORTHO drape image. Idrisi has two functions which produce an image of this type. The first, the ORTHO module, produces static images from preset viewing angles and elevations. This is useful for making final images for presentation, or for emphasizing certain features in a publication. The other function is an interactive function called the "FLYTHROUGH" module. This module uses the OpenGL resources in most reasonably modern computers to allow rapid scaling and motion in relation to the three-dimensional draped image. It is worth noting that this technology, like much graphic technology in modern comptuers, was pushed heavily by the computer gaming industry. A still screen-capture is shown, demonstrating one viewing position and angle during the manual "fly through" sequence.
|A false-color infrared composite was created by using the COMPOSITE module to combine the blue, green, and near-infrared IKONOS bands. The resulting composite was draped over the final DEM model arrived at through the manipulations described in the DEM section above.|
|See image annotation.|
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This project has demonstrated the procedures used to import, process, and display GIS data in a manner which increases the usefulness of the data at hand. I encountered significant problems with data compatibility, and overcame those problems to successfully produce ORTHO and FLYTHROUGH images.
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Why is this document so simple? Concise hand coding in simple HTML.
For more information, see the NCSA (at UIUC) Beginners Guide to HTML.
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James K. Deane, ES 551 / Copyright 2004 JKD
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