P-Band Radar Retrieval of Permafrost Active Layer Properties: Time-Series Approach and Validation with In-Situ Observations

In this paper, a permafrost active layer retrieval algorithm using time-series P-band SAR observations is presented wherein both layer dielectric constants (representing unfrozen water content) and layer thicknesses (representing water table or thaw depths) of the active layer are retrieved. The time-series observations were acquired after the maximum thaw, so that variables such as active layer thickness (ALT) can be assumed constant as they are nearly time-invariant between the data acquisitions. Having these time-invariant variables can reduce the number of unknowns and improve the retrieval accuracy with limited number of observations. Comparison of the retrieval results with in-situ observations suggests that the retrieved ALT values are generally underestimated.