Four-Band Image Mosaic of the Colorado River Corridor Downstream of Glen Canyon Dam in Arizona, Derived from the May 2013 Airborne Image Acquisition

Data Organization

The 16-bit image data are stored as four-band images in embedded geotiff format, which can be read and used by most geographic information systems (GIS) and image-processing software. TIFF world files (tfw) are provided; however, they are not needed for many software programs to read an embedded geotiff image. The image files are projected in the State Plane map projection using the central Arizona zone (202) and the North American Datum of 1983 (NAD83). The map-tile scheme used to segment the image mosaic follows the standard USGS quarter-quadrangle (QQ) map borders, but the high resolution (20 cm) of the images required further quarter segmentation (QQQ) of the standard QQ tiles, where the image mosaic covered a large fraction of a QQ map tile. To minimize the size of each image tile, each image or map tile was subset to include only that part of the tile which contained image data. In addition, some QQQ image tiles within a given QQ tile were combined when adjacent QQQ map tiles were small. Thus, some image tiles consist of combinations of QQQ map tiles, some of an entire QQ map tile, and some of two adjoining QQ map tiles. A total of 144 image tiles are in the final mosaic dataset. The image tiles are placed in seven file folders based on the half-degree geographic boundaries within the study area (fig. 3). The file folders are sequentially referred to as zones 1 through 7, beginning at Glen Canyon Dam and proceeding downriver. The QQ designations of the image tiles contained within each folder or zone are shown on the index map for each respective zone.