Retrieving Temperature Gradient in Frozen Active Layer of Arctic Tundra Soils From Radiothermal Observations in $L$-Band—Theoretical Modeling

Possibility of remote sensing of both the surface temperature and the temperature gradient in the permafrost active layer from
L
-band brightness temperature observations is theoretically investigated at a SMOS frequency of 1.4 GHz. Bare soil emission is simulated based on the semi-empirical L-MEB model. The brightness temperature is simulated using the soil density, surface roughness, temperature, and moisture profiles measured in situ at the Biosphere Station Franklin Bluffs, Alaska, USA (69°39'N, 148°43'W) from September 2, 1999, to August 23, 2001. The soil permittivity is calculated using the temperature-dependent generalized refractive mixing dielectric model for the organic rich soil sample collected in North Slope, Alaska (68°38'N, 149°35'W). This model predicts the complex dielectric constant of moist soil both thawed and frozen at temperatures from -30°C to +25°C and moistures from 0 to 0.94 g/g. The brightness temperatures simulated for field-of-view angles from 0 to 60° are inverted into the temperature profiles, and their deviations from the temperature profiles measured in situ are estimated. The error in reconstructing temperature profiles is found to be no greater than 1.8°C to depths of 0.15 m.