A comparison of optical-band based snow extent products during spring over North America

We find that on seasonal time scales, the most pronounced differences between the IMS and MODIS snow products occurs during the ablation season over North America. Our results corroborate earlier studies showing pronounced differences over the northern tundra in June, where MODIS appears to be in agreement with other observations; as well as differences in April and May in the boreal forest, where evidence suggests that both products may be biased (although MODIS biases may be smaller) in comparison with the CMC product (which is based on station observations). The influence of clouds may be a factor even though the analysis includes only clear days. Another possible explanation for these discrepancies involves the impact of numerous small lakes over the North American landscape on the interpretation of satellite retrievals in the visible band, although there are other potential sources of error in both products. For example, comparison to the CMC reanalysis suggests that MODIS may be overestimating snow during the ablation season in the boreal forest. The resolution of these discrepancies may affect our understanding of the seasonal snow cover cycle, the evaluation of and development of parameterization schemes for climate models, and the development of a climate data record for snow cover.