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<br />. . . <br /> <br />snowplowed traffic areas. Despite the relatively small size of the <br />communities, Craig and Steamboat Springs were easily identified on the <br />Landsat image for February 25, 1975 (fig. 5). Smaller communities, such as <br />Hayden, Colo. (estimated population of about 1,800 in 1975), could be <br />identified on the image with prior information on their location. U.S. <br />Highway 40, the major two-lane east-west highway in the basin, is visible <br />except In areas shaded by steep relief. Although the highway has a pavement <br />width less than the resolution of a pixel (see Glossary), it is visible <br />because of its extended linear trend and its contrast with surrounding snow <br />cover. With high contrast conditions, extended linear features as small as <br />50 ft (15 m) wide may be detected (Wiedel and Kleckner, 1974). Other paved <br />highways in the basin can be identified only in segments, because they have <br />less traffic or may be shaded by adjacent steep relief. <br /> <br />A combination of the band-7 black-and-white image for February 25, 1975, <br />and the color-composite image for August 24, 1975, was used to locate active <br />surface mines. Surface mines in the basin are difficult to find on the <br />images without prior information regarding their general location. However, <br />once located on the images, active mined areas generally can be delineated <br />and their areal extent determined. Active mines appear dark on the winter <br />black-and-white photograph, contrasting with the surrounding snow. On summer <br />color-composite images, active surface mines are characterized by a <br />combination of hue (blue gray to black) and sometimes distinctive spatial <br />characteristics. Older abandoned and unreclaimed surface mines were very <br />difficult to locate on the satellite imagery in most instances. This was <br />because rangeland vegetation had established itself on the mine spoils, <br />giving these areas spectral characteristics similar to sparsely vegetated <br />rangeland. The small-scale resolution of the Landsat MSS (see Glossary) is <br />generally not sufficient to depict the I ined-row characteristic of the <br />unreclaimed spoils once natural vegetation has begun to establish itself on <br />them. Most of the present and past surface-mining operations in the Yampa <br />River basin are located in areas of a mixed rangeland category of land use so <br />that they contrast much less with surrounding areas than do mines located <br />in forested regions. Also, unl ike eastern surface-mining operations, <br />individual strips do not follow the terrain contours, which tend to make them <br />less distinctive on Landsat images. <br /> <br />Analysis by digital-image processing was conducted using both the Image- <br />100 System and IDIMS. Both systems were selected because each contained <br />different classification functions (p. 48) which afforded the opportunity to <br />maximize the number of analysis techniques that could be evaluated for land- <br />use classifications. <br /> <br />The August 24, 1975, Landsat image was selected for digital analysis to <br />determine land-use classes. The emphasis was on determining the categories <br />of land use that could be identified by this method and the level of <br />classification (table 2) that was possible within each of the categories. <br />Comparison of several different classification functions allowed evaluation <br />of the relative merits of each of the functions for land-use classification <br />and mapping. <br /> <br />12 <br />