Incidence Angle Dependence of First-Year Sea Ice Backscattering Coefficient in Sentinel-1 SAR Imagery Over the Kara Sea

We have studied the incidence angle (theta(0)) dependence of the sea ice backscattering coefficient (sigma degrees) for Sentinel-1 (S-1) extra wide (EW) mode dual-polarization (HH/HV) synthetic aperture radar (SAR) imagery acquired over the Kara Sea under winter and summer melting conditions. The determination of the sigma degrees versus theta(0) dependence was based on SAR image pairs acquired on ascending and descending orbits over the same sea ice area with a short time difference. The SAR noise floor was subtracted from the HV images. From the image pairs 1.1 by 1.1 km windows representing level first-year ice (LFYI) and deformed first-year ice (DFYI) were manually selected, and a linear regression was fit between the resulting sigma degrees and theta(0) differences of the windows to estimate the slope b(1) (dB/1 degrees) between sigma degrees and theta(0). For example, under winter condition b(1) for DFYI at HH- and HV-polarizations was found to be -0.24 and -0.16 dB/1 degrees, respectively, and b(1) for LFYI at HH-polarization was -0.25 dB/1 degrees. It was not possible to determine a reliable b(1) for LFYI at HV due to a contamination effect of the S-1 noise floor. The b(1) values at HH compared well with previous studies. They can be used to compensate the sigma degrees incidence angle variation in the S-1 EW SAR images with good accuracy. The HH b(1) values are applicable to other S-1 imaging modes and other C-band SAR sensors like RADARSAT-2. Unfortunately, the HV b(1) values are specific to the S-1 EW mode due to the noise floor problem.