The raster land use/land cover data is a geo-referenced, thematic data layer produced using multi-date 2005 Landsat 5 Thematic Mapper satellite imagery. The satellite imagery used in the classification was collected between the dates of 06/13/2005 and 9/20/2005. The satellite imagery was obtained with radiometric and terrain correction. Cloud coverage dictated date selection to the greatest extent, although imagery were chosen to represent spring, summer, and fall growing conditions. The nominal scale is 1:100,000 with a ground resolution of 28.5 meters or 93.48 feet.
Spectral signatures for each class were extracted and evaluated for continuity. Unrepresentative signatures were deleted. The remaining signatures were then used in a supervised classification on the multi-date imagery. After the classification algorithm was run, classes were evaluated for accuracy. Many techniques were applied to compensate for mixed classes. Clouded areas were classified in a second stage, using an unsupervised classification with the remaining unclouded dates.
Urban areas were defined using 2000 TIGER census data, 2003 and 2005 Farm Service Agency (FSA) Ortho Imagery. Field data for crops were obtained during the 2005 growing season from Natural Resources Districts across the state. 2003 and 2005 FSA Ortho Imagery were used to locate spectral signature for riparian and forested areas, roads, and non agricultural features.
Irrigation information was obtained from the Nebraska Department of Natural Resources, Public Power Districts, Nebraska Natural Resource Districts, and the 2001 COHYST land use data. Center pivots were on-screen digitized using the 2005 Landsat TM data and the 2005 FSA Ortho Imagery.
Once the land cover classification was completed, a 3x3 majority filter was applied to agricultural classes to minimize the remaining mixed pixels. There are 25 classes and crops identified as either irrigated or dry land. The overall accuracy for the classification was calculated at 80.66%. This project was part of a joint research project with the Nebraska Department of Natural Resources