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.

Climate projections of sea ice retreat under anthropogenic climate change at the regional scale and in summer months other than September have largely not been evaluated. Information at this level of detail is vital for future planning of safe Arctic marine activities. Here the timing of when Arctic waters will be reliably ice free across Arctic regions from June to October is presented. It is shown that during this century regions along the Northern Sea Route and Arctic Bridge will be more reliably ice free than regions along the Northwest Passage and the Transpolar Sea Route, which will retain substantial sea ice cover past midcentury. Moreover, ice‐free conditions in the Arctic will likely be confined to September for several decades to come in many regions. Projections using a selection of models that accounts for agreement of models in each region and calendar month with observations yield similar conclusions.

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This paper presents results comparing digitized seaice charts with passive microwave estimates of sea-ice concentration using the NASA Team algorithm. The Canadian ice chart series contains detailed information on sea-ice type during the sea ice growth, consolidation and melt stages for four main ice-covered regions of Canada: the Canadian East Coast, Hudson Bay, East Canadian Arctic and the West Canadian Arctic.Comparison with passive microwave sea-ice concentration estimates over the 1979 to 1996 period shows the consistency with which sea-ice concentration and sea-ice area are underestimated by the passive microwave data during melt and freeze-up conditions.

ABSTRACT. Changing Arctic sea-ice extent and melt season duration, and increasing economic interest in the Arctic have prompted the need for enhanced marine ecosystem studies and improvements to dynamical and forecast models. Sea-ice melt pond fraction f p has been shown to be correlated with the September minimum ice extent due to its impact on ice albedo and heat uptake. Ice forecasts should benefit from knowledge of f p as melt ponds form several months in advance of ice retreat. This study goes further back by examining the potential to predict f p during winter using backscatter data from the commonly available Sentinel-1 synthetic aperture radar. An object-based image analysis links the winter and spring thermodynamic states of first-year and multiyear sea-ice types. Strong correlations between winter backscatter and spring f p , detected from high-resolution visible to near infrared imagery, are observed, and models for the retrieval of f p from Sentinel-1 data are provided (r 2 ≥ 0.72).The models utilize HH polarization channel backscatter that is routinely acquired over the Arctic from the two-satellite Sentinel-1 constellation mission, as well as other past, current and future SAR missions operating in the same C-band frequency. Predicted f p is generally representative of major ice types firstyear ice and multiyear ice during the stage in seasonal melt pond evolution where f p is closely related to spatial variations in ice topography.