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Poon, SKM, Valeo, C (2006). Investigation of the MODIS snow mapping algorithm during snowmelt in the northern boreal forest of Canada. CANADIAN JOURNAL OF REMOTE SENSING, 32(3), 254-267.

A major limitation in mapping snow-covered area (SCA) when using optical satellite sensors is encountered in forested areas, particularly during snowmelt. Consequently, using land cover information to map snow in heterogeneous environments that include dense forest might provide a solution. This study investigated the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center version 4 snow mapping algorithm developed for the moderate resolution imaging spectroradiometer (MODIS) Terra sensor. The functionality of this algorithm for mapping snow during the snowmelt period in the northern boreal forest of Manitoba was tested by comparing the results of this algorithm with those produced by two other algorithms that rely on land cover data instead of the normalized difference vegetation index (NDVI). Comparisons are also made between these three algorithms and the SCA provided by the MOD10A1 MODIS Terra product. For the 2001 snowmelt period, the results from the algorithms and the Terra product showed no noticeable difference in the amount of SCA predicted, but a difference of as much as 20% existed over the 2002 melt period, with the MODIS product predicting more snow than the algorithms. Atmospheric corrections and thresholds used to detect dark targets also had noticeable influences on the amount of SCA predicted by the algorithms. The location of areas mapped with snow also differed between the algorithms and the MOD10A1 product. The agreement in the location of SCA between that predicted by the algorithms and that provided by MOD10A1 differed by as much as 75% towards the end of the 2001 melt period, and even larger discrepancies were observed in 2002. Analysis indicated that the greatest differences occurred in marsh and coniferous areas, and this was consistent throughout the melt period. In addition, higher elevations caused the greatest differences in early stages of the melt period, but lower elevations contributed to the differences in later stages of melt. SCA data for both years showed an exponential correlation with accumulated degree-days for 2001, 2002, and 2003, but the relationship varied depending on the length of the melt period. Snow depletion behavior at different elevation ranges in the study area indicated that snow located at higher elevation ranges melted faster than snow located at lower elevation ranges for 2001, 2002, and 2003. This analysis is based on the MODIS Terra version 4 snow mapping algorithm (as opposed to the algorithm used for the MODIS Aqua sensor), and it is still the most up-to-date version as of early 2006.



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