Smap Vegetation Optical Depth Retrievals Using The Multi-Temporal Dual-Channel Algorithm

The multi-temporal dual-channel algorithm (MT-DCA) is reviewed in its approach in simultaneously estimating soil moisture and vegetation optical depth (VOD) from SMAP brightness temperature (TB) measurements. At a single incidence angle, the two polarized TB measurements from SMAP at a given location do not provide two degrees of information (DOI). Therefore, this approach assumes a constant VOD between SMAP overpasses to increase DOI and stabilize the soil moisture-VOD estimation. Retrieved time-mean VOD covaries spatially with vegetation biomass, but its temporal dynamics have yet to be validated with in-situ measurements. Recent SMAP VOD applications in plant ecology and crop monitoring are discussed. Ultimately, these studies suggest insightful vegetation information is present in both weekly and seasonal SMAP VOD variations. Further study and ground monitoring campaigns will continue to reveal the extent of geophysical information in the VOD signal.