Using Satellite Imagery to Inventory Irrigated Lands in the Upper Colorado RiverBasin

摘要

Landsat Thematic Mapper (TM) and SPOT High Resolution Visible (HRV) satelliteimages were acquired during the 1995 growing season for the 113,000-square-mile Upper Colorado River Basin. The image data were used in conjunction with a previously developed vector-based 1:24,000 scale digital data set to produce an irrigated lands inventory. Scenes were calibrated to surface reflectance to minimize image variation caused by nonsurface factors. A TM Tasseled Cap transform was applied to calibrated images to reduce data volume and provide easily interpretable output images. Spectral-space decision thresholds were derived from a 50-percent random sample of extensive field data. A classification model applied these thresholds to the image data, resulting in an eight-class thematic map. Irrigated acreages were calculated through pixel summing. The vector data were used to mask out nonagricultural lands and to privide irrigated acreage estimates for areas obscured by clouds. A total of 1,845,382 acres was mapped as irrigated in 1995.