Estimating firn temperatures in Greenland and Antarctica from dual polarization C-band microwave emission observations

Studies surface-based observations of C-band emission and firn layering at four sites in Antarctica made by R. Rott showing the variation of brightness temperatures with variations in centimeter-scale density fluctuations in the upper few meters of firn. The authors present (1) a signature model based on scattering from centimeter-scale layers and Monte Carlo averaging over ensembles of such layers, and (2) an objective statistical procedure for deriving parameters of a stochastic model for firn layering from the available ground truth observations. The authors find very good agreement between signatures predicted by the model and ground-truth inputs and emission observations at three of the sites, using essentially no free parameters or model fitting. At the fourth site, layering was too fine to be effectively resolved by the ground-truth measurements, but the observed signatures can be explained by their model using layering parameters consistent with the observations. Layering significantly lowers brightness temperatures and increases the the difference between vertically and horizontally polarized emission. These changes depend most sensitively on the mean layer thickness and variance of density fluctuations from layer to layer. The effect of layering on vertically polarized emission near 50 degrees nadir angle is non-negligible but small. Thus layering effects can be effectively corrected out of vertically-polarized brightness temperatures using dual polarization observations, to produce a “brightness temperature” more simply related to the profile of physical temperature in the firn. The authors present a method to estimate firn temperatures and test the method using the ground-based data