Incidence Angle Dependencies for C-Band Backscatter From Sea Ice During Both the Winter and Melt Season

• Published in: IEEE transactions on geoscience and remote sensing Vol. 61; pp. 1 - 15
• Main Authors: Geldsetzer, Torsten, Howell, Stephen E. L.
• Format: Journal Article
• Language: English
• Published: New York IEEE 2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Backscatter; Backscattering; C band; Incidence angle; Mental task performance; Ponding; Radar imaging; Radar polarimetry; RADARSAT Constellation Mission (RCM); SAR (radar); Scattering; Sea ice; Seasons; Slope; Slopes; Snow; Snowmelt; Synthetic aperture radar; synthetic aperture radar (SAR); Visual system; Winter
• ISSN: 0196-2892; 1558-0644; 1558-0644
• DOI: 10.1109/TGRS.2023.3315056

Incidence angle normalization is used to reduce the radiometric ambiguity within or between synthetic aperture radar (SAR) images. For sea ice, incidence angle normalization is typically constrained to winter months because of the difficulty of capturing the rapidly changing backscatter values during the melt season. Here, we make use of high-temporal-resolution RADARSAT Constellation Mission (RCM) SAR images to quantify incidence angle dependencies (slopes) for first-year ice (FYI), second-year ice (SYI), and multi-year ice (MYI) during several stages of melt. We apply a new successive image differencing method to mitigate the rapid changes in backscatter during the melt season. Slopes for SYI are shown, for the first time, for winter, and for most melt season periods. Time series of slopes are shown, also for the first time, at intervals as short as 30 min. Slopes for the early melt period (FYI: −0.230; SYI: −0.191; and MYI: −0.175 dB/1°) are similar to those for winter (FYI: −0.235; SYI: −0.208; and MYI: −0.167 dB/1°). During the snowmelt period, slopes remain similar to winter for FYI (−0.235 dB/1°) but become steeper for SYI (−0.241 dB/1°) and MYI (−0.240 dB/1°). All ice types reach their maximum slope steepness during the ponding period (FYI: −0.308; SYI: −0.283; and MYI: −0.289 dB/1°) and then become shallower again during the drainage period (FYI: −0.198; SYI: −0.207; and MYI: −0.240 dB/1°). We show that the melt-season-specific slopes provide important improvements for the visual interpretation of SAR imagery and in backscatter consistency for automated classification algorithms.