CoAuthors

Lisa Recchia (Aresys S.r.l., Italy); Michele Scagliola (Aresys S.r.l., Italy); Pietro Guccione (Aresys S.r.l., Italy)

This abstract focuses on the description and the preliminary validation of a model-based retracker for sea ice covered regions. Retracking is carried out by fitting an adaptation of the semianalytical model described in [1] to altimeter power waveforms acquired over Arctic sea ice to retrieve values of surface elevation, backscattering efficiency, surface roughness, snow depth and a normalized multilooked peak power. Curve fitting is performed using the Levenberg–Marquardt algorithm which fits the specific model function—i.e. the objective function—to the altimeter power waveform. The potential advantages of such a model-based approach would be, e.g., to account for the elevation bias introduced by threshold retrackers over sea ice and leads, caused by varying surface roughness and by the empirical choice of retracking thresholds.
Preliminary validation of the retracker is performed by comparing CryoSat along-track elevations with those obtained by the SAMOSA+ retracker. Additionally, freeboard estimates from the semianalytical reracker are compared with Operation IceBridge data collected during CryoSat underflights in the Arctic. In order to assess the potential advantage of a joint retracking of sea ice freeboard and snow depth, we investigate differences in freeboard estimates from the semianalytical retracker computed in three different ways: by not applying the snow model, by considering a constant value of snow depth along specific CryoSat tracks, and by attempting to directly retrack the snow depth.

[1] Recchia, L., Scagliola, M., Giudici, D. & Kuschnerus, M. An Accurate Semianalytical Waveform Model for Mispointed SAR Interferometric Altimeters. IEEE Geoscience and Remote Sensing Letters 14, 1537–1541 (2017).