Ground-reference techniques for the Enhanced Thematic Mapper Plus (ETM+) on Landsat 7 are described. The reflectance-based approach for vicarious calibration has been applied by the Remote Sensing Group of the Optical Sciences Center to 59 sets of ground-based data collected at large uniform test sites imaged by Landsat-7 ETM+. The results of this work coupled with the apparent stability of the ETM+ sensor shows that a one-sigma precision less than 3% is currently being achieved. Band-by-band analysis of the precision gives insight into the effects of atmospheric correction and surface reflectance uncertainties giving an understanding of the error sources in this approach. Variations in results are not seen between test sites and atmospheric effects are not the primary cause of day-to-day variability. These results are discussed with an emphasis on the current state of vicarious calibration accuracies/precision as well
as areas for improvement and future accuracy expectations.
Recent results of the vicarious calibration of the Landsat-7 ETM+ sensor are presented based on the reflectance-based vicarious method using results from a smaller test site in close proximity to the University of Arizona. The typical, larger test site is brighter and more spatially uniform then the smaller site. However, the location of the small test site allows for more frequent data collections and a more complete understanding of the calibration coefficients of the sensor as a function of time. The Remote Sensing Group previously reported results based on data collected from the smaller test site on seven dates. Here we report calibration values for additional dates as well as a comparison of the calibration values for the large and smaller test sites over recent years. The most recent data shows the calibration values using the smaller sites continue to agree within 3% of the large test sites in all bands.