Estimation of relative canopy absorption and scattering at L-, C- and X-bands

摘要

Quantification of microwave vegetation properties (i.e. vegetation optical depth (VOD) and single scattering albedo (omega)) is of interest not only to reliably estimate soil moisture from the Earth's microwave emission, but also for broad applications across plant physiology and hydrology. Estimated VOD is often used as a biomass proxy or to investigate plant water dynamics on multiple scales, as it is dependent on the vegetation water content, dry woody biomass, and canopy structure. For most but not all microwave satellite remote sensing applications, VOD and omega are assigned a priori from auxiliary vegetation information and used as inputs to retrieve soil moisture. Alternatively, polarized brightness temperature has been used to estimate VOD and omega. Retrieval algorithms typically use the zeroth-order solution to the radiative transfer equation (tau-omega model) to simultaneously characterize surface and vegetation emission. In this study we investigate one year of estimated VOD and omega at L-(1.4 GHz), C-(6.9 GHz) and X-band (10.7 GHz), from SMAP and AMSR2 satellites respectively. Since VOD and omega describe absorption and scattering integrated over a path length, we derive estimates of relative absorption and scattering through normalization by a vegetation height derived from GLAS light detection and ranging (lidar) measurements.