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The European Space Agency's CryoSat‐2 satellite mission provides radar altimeter data that are used to derive estimates of sea ice thickness and volume. These data are crucial to understanding recent variability and changes in Arctic sea ice. Sea ice thickness retrievals at the CryoSat‐2 frequency require accurate measurements of sea ice freeboard, assumed to be attainable when the main radar scattering horizon is at the snow/sea ice interface. Using an extensive snow thermophysical property dataset from late winter conditions in the Canadian Arctic, we examine the role of saline snow on first‐year sea ice (FYI), with respect to its effect on the location of the main radar scattering horizon, its ability to decrease radar penetration depth, and its impact on FYI thickness estimates. Based on the dielectric properties of saline snow commonly found on FYI, we quantify the vertical shift in the main scattering horizon. This is found to be approximately 0.07 m. We propose a thickness‐dependent snow salinity correction factor for FYI freeboard estimates. This significantly reduces CryoSat‐2 FYI retrieval error. Relative error reductions of ~11% are found for an ice thickness of 0.95 m and ~25% for 0.7 m. Our method also helps to close the uncertainty gap between SMOS and CryoSat‐2 thin ice thickness retrievals. Our results indicate that snow salinity should be considered for FYI freeboard estimates.

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A portable surface-based polarimetric C-band scatterometer for field deployment over sea ice is presented. The scatterometer system, its calibration, signal processing, and near-field correction are described. The near-field correction is shown to be effective for both linear polarized and polarimetric backscatter. Field methods for the scatterometer are described. Sample linear polarized and polarimetric backscatter results are presented for snow-covered first-year sea ice (FYI), multiyear hummock ice, and rough melt pond water on FYI. The magnitude of backscatter signature variability due to system effects is presented, providing the necessary basis for quantitative analysis of field data.

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Compact-polarimetry (CP) SAR observations are presented for major sea ice types in each ice season. CP data for three wide-swath Radarsat Constellation Mission (RCM) modes were simulated and evaluated. Regression models, and statistical distances, as functions of incidence angles, were calculated for 26 CP parameters, based on 969 samples of user-selected homogeneous regions of sea ice. CP parameters, best able to discriminate sea ice types and open Downloaded by [University of Nebraska, Lincoln] at 00:10 31 December 2015 ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 water, were quantitatively identified in three incidence angle ranges (19-29°, 30-39°, 40-49°).These parameters will likely provide discrimination of sea ice types and open water, for both visual interpretation and automated classification. Several parameter-ice type combinations exhibit novel scattering responses, which present new opportunities for ice type discrimination and for inferring scattering mechanisms. Specifically, phase-related parameters with early-stage ice types provide discrimination for ice type pairings that are difficult with co-or dual-polarized data. CP parameters change with incidence angle, which necessitates the use of certain CP parameters at smaller incidence angles and others at larger incidence angles in wide-swath RCM modes. The Canadian Ice Service will implement CP SAR data in their operational work-flows once the RCM is operational. Pre-launch study results provide a valuable resource for early adoption of CP data. Résumé.Des observations SAR en polarimétrie compacte (CP) sont présentées pour les principaux types de glace de mer pour la saison des glaces. Des données en CP pour trois modes à large fauchée de la mission de la Constellation RADARSAT (MCR) ont été simulées et évaluées.

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