Creation of ersatz ground reference data for validating the MODIS snow and ice product suite

We have developed a photo-interpretive tool for editing the MODIS snow cover data products to produce an ersatz (i.e., substitute) ground reference for use in evaluating approaches for improving product accuracy. This tool enables an analyst to compare visualizations of Landsat scenes with registered sub-sections of MODIS scenes and edit the product as indicated. We provide an example of the use of this tool for a MODIS scene in which cloud mask errors are corrected and where the cloud mask is removed where snow or land is clearly seen through thin clouds. The resulting revision increased the snow coverage area from 10.9% to 16.0%, and decreased the cloud coverage from 37.9% to 27.9%. However, when the original cloud mask is applied to the revised snow map, the revised map agrees to 99.64% with the original snow map, indicating very little change in snow labeling outside changes in the cloud mask.