Depth dependence of snow brightness temperature on sea ice

Discusses the depth dependence of brightness temperature of a snow layer on sea ice, observed at 6.7 and 18.6 GHz, theoretically, applying a microwave radiative transfer model. Upward and downward radiations in the snow layer are assumed to be diffuse and formulated by two flow theory from the fact that the brightness temperature shows neither marked incidence angle dependence nor distinct polarization due to significant multiple scattering at larger depths. This model enables the authors to derive a depth dependence model of snow brightness temperature, which is then compared with observations at 6.7 and 18.6 GHz. It is concluded from both model estimation and observation that the snow brightness temperature monotonously increases with depth toward an asymptotic value which is around 250 K and 240 K at 6.7 and 18.6 GHz, respectively, and neither a local maximum nor local minimum exists. This model is modified into a frequency dependent model, which shows that the brightness temperature is more sensitive to change in depth at smaller depths and no sensitivity is seen at larger depths in the frequency range from 20 to 30 GHz. However, the change in depth effects the brightness temperature even for 2-m deep snow cover at lower frequencies around 5 GHz