Sea Ice Freeboard Extrapolation from ICESat-2 to Sentinel-1

Abstract. The ICESat-2 laser altimeter can capture sea ice freeboard along track at both high vertical and high spatial resolution. The measurement occurs along three strong and three weak parallel beams. Thus the across track-direction is only very sparsely covered and capturing the two-dimensional spatial distribution of freeboard at high resolution by this instrument alone is not possible. This work shows how in early Arctic Winter (October, November) Sentinel-1 synthetic aperture radar (SAR) acquisitions can help bridge this gap and meaningfully extrapolate the freeboard measurements to a full two-dimensional mapping. To achieve this it is sufficient to use the SAR HV backscatter to sort the pixels by intensity and then map freeboards measured from altimetry in the area via the cumulative distribution functions. With the presented algorithm, snow and ice freeboard derived from altimetry can be meaningfully extrapolated to Sentinel-1 SAR acquisitions, unlocking an extra dimension of Arctic freeboard monitoring at high spatial resolution, with errors between 10.5 cm and 6 cm for resolutions between 100 m and 400 m.