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Science for Watershed Decisions on Abandoned Mine Lands: Review of Preliminary Results, Denver, Colorado, February 4-5, 1998

Digital Data for Watershed Characterization of Abandoned Mine Land

By E. Paul Martin¹

The USGS produces a number of standard digital products that represent base cartographic, elevation, and image information in support of a wide range of applications. In some applications, these data act strictly as a reference or background cover, and in some cases, these data are integrated with scientific information to form a knowledge base for subsequent analysis and decision making. Both cases apply to the USGS abandoned-mine- land project in order to characterize the watersheds.

A digital elevation model (DEM) provides an array of elevation values that represent the terrain. When brought into a geographic information system, the software can transform the grid values into a shaded relief topographic view. While certain features are easily discernible, the DEM does not present a true picture of the ground features. A digital orthophoto quadrangle (DOQ) yields a clear view of these ground features. The DOQ is an image product derived by differential rectification from a perspective aerial photograph or other remotely sensed image data. Image displacements caused by camera tilt and terrain relief are removed. The DOQ combines the image characteristics of a photograph with the geometric qualities of a map. The DEM and DOQ in concert render a unique representation in which both the elevation and natural and cultural features are accentuated. The DOQ provides a source from which to ground truth existing vector data (for example, a digital line graph's (DLG) spatial location) or from which to compile new cultural and natural features. The combination of DEM and DOQ with DLGs (or other vector data) draped over the landscape gives a comprehensive watershed view. With the addition of more detailed scientific information and coverages (for example, water-quality data, dump-site characteristics, and geology), one now has the watershed information from which to perform more detailed analysis within the geographic information system or other modeling software.

¹U.S. Geological Survey, MS 516, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (epmartin@usgs.gov)

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