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.