Global estimates of L-band vegetation optical depth and soil permittivity of snow-covered boreal forests and permafrost landscape using SMAP satellite data

Abstract

The tau-omega model is expanded to properly simulate L-band microwave emission of the soil–snow–vegetation continuum through a closed-form solution of Maxwell's equations, considering the intervening dry snow layer as a loss-less medium. The error standard deviations of a least-squared inversion are 0.1 and 3.5 for VOD and ground permittivity, over moderately dense vegetation and a snow density ranging from 100 to 400 kg m−3, considering noisy brightness temperatures with a standard deviation of 1 kelvin. Using the Soil Moisture Active Passive (SMAP) satellite observations, new global estimates of VOD and ground permittivity are presented over the Arctic boreal forests and permafrost areas. In the absence of dense in situ observations of ground permittivity and VOD, the retrievals are causally validated using ancillary variables including ground temperature, above-ground biomass, tree height, and net ecosystem exchange of carbon dioxide. Time-series analyses promise that the new data set can expand our understanding of the land–atmosphere interactions and exchange of carbon fluxes over Arctic landscapes.