Implications and Applications of Emerging Polarimetric Synthetic Aperture Radar for the Retrieval of Freshwater Ice Properties

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Over one-quarter of Earth's lakes are located in northern regions and experience seasonal ice development and decay. The rate at which physical components of the Arctic landscape are changing in the face of amplified warming is of importance for habitat, sustainable community development, and infrastructure considerations. In particular, seasonal ice growth, phenology (timing of freeze-up and break-up), and ice thickness provide a proxy for monitoring climate, and are Essential Climate Variables in the Global Climate Observing System. Remote sensing utilizing microwave frequencies have been particularly useful for retrieving ice properties. Recent studies have identified the source of backscatter in lake ice is roughness at the ice bottom, allowing for the potential to derive ice thickness and map the contour of the ice-water interface. A necessity in mapping the ice bottom is to retain coherence, which describes the similarity of radar reflection of a target and incidence angle between two images. Retaining coherence for ice may now be a possibility using two new sensors: Radarsat Constellation Mission (RCM), and NISAR. RCM (C-band 5.5 cm) allows for repeat passes every 4 days, improving temporal resolution and reducing the amount of ice growth between acquisitions. NISAR is a planned polarimetric interferometric Synthetic Aperture Radar mission scheduled to launch in 2022 with L- (24 cm) and S-band (12 cm) and 12 day repeat pass. The long wavelengths observed by NISAR could exceed ice growth between acquisitions, allowing for retained coherence. RCM's launch presents a new beam mode: compact polarimetry (CP). CP sends circularly polarized waveforms and receives vertical and horizontal polarizations. There have been few studies that have addressed CP observations of freshwater ice, having only used CP simulations from Radarsat-2 scenes. Preliminary results from simulated CP data indicate that ice parameters can be retrieved (ice extent and break-up), but tests have not used actual RCM acquisitions. The overarching goal of my research program is to improve the application of new sensors and beam modes interacting with freshwater ice to retrieve and communicate ice parameters to invested stakeholders. Additionally, this research will provide a baseline of retrievals as a blueprint to be applied to the growing database of RCM CP and NISAR acquisitions. This research program is uniquely positioned to develop preliminary CP ice algorithms as Canada's flagship satellite transitions to collect predominantly in CP mode, and will lay the foundation of ice retrieval algorithms at a Pan-Canadian scale, and globally when NISAR's acquisitions begin. The work is of critical importance for the understanding of hydrological processes in Canada's sub-Arctic and Arctic regions, with retrieved ice parameters directly benefitting communities' access to ecosystem services (e.g. transportation over ice, overwintering fish habitat, and available water resources).