Geophysical and Atmospheric Controls on L-band Synthetic Aperture Radar Backscatter From Sea Ice: Insights From a Surface-Based Polarimetric Scatterometer

This study is motivated by the development and pending launch of new L-band synthetic aperture radar (SAR) missions such as the Copernicus Radar Observation System for Europe in L-band (ROSE-L) and the NASA-ISRO SAR Mission (NISAR). The open data policy and regular coverage of polar oceans from these missions will broaden the capability of L-band SAR as a standalone or complementary (e.g. with C-band) sensing technology for sea ice geophysical information retrievals and climate research. In this study, controls on time-varying L-band frequency polarimetric backscatter are examined using measurements from a sled-mounted L-band frequency (1.3 GHz) radar scatterometer system deployed during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The system collected data from drifting central Arctic sea ice across a wide incidence angle range and from a small field of view (metre scale) over an annual cycle including freeze-up, winter, and melting periods. This system operated at the lowest frequency of the active microwave instrumentation at MOSAiC, providing deeper relative penetration and novel insights into the seasonally evolving and event-driven internal ice physical and thermodynamic properties. Here, the signature controlling properties of sea ice are examined in the context of corresponding satellite L-band synthetic aperture radar observations from MOSAiC (ALOS-2/PALSAR-2 and SAOCOM), as well as pending missions like NISAR and ROSE-L. Comparisons are made to data collected at higher frequencies (C-, X-, and Ku- band) in efforts to better understand the roles of snow cover and surface melt on active microwave signatures and for development of improved SAR and radar altimeter retrievals.