New Approaches for Removing the Effect of Water Damping on SMAP Freeze/Thaw Mapping

摘要

The Northern Quebec landscape is typically covered by numerous lakes. The lowest emissivityof water bodies dominates the brightness temperature (Tb) data measured over this region.Thus, it is necessary to eliminate the effect of water bodies from Tb measurements. The primaryobjective of this study is to develop two approaches to correct the Soil Moisture ActivePassive brightness temperature (SMAP L1C), collected between January and December of2016, for the damping effect of water bodies within each 36km by 36km pixel. The first algorithmnormalizes Tb with the intercept of its linear regression versus the water fraction ofeach pixel. A second algorithm used Tb regression with water fraction by vegetation classesfor each scene. Surface soil temperature and moisture measured near Umiujaq were used tovalidate Tb correction. The proposed Tb corrections resolve the divergence observed withSMAP standard correction when the water fraction is higher than 20%. Corrected brightnesstemperature is then tested for mapping the soil freeze/thaw state using the NormalizedPolarization Ratio. Agreements of up to 90% (ascending orbit) and 79% (descending orbit)were reached for the proposed approach versus 64% and 50% for the existing approach.