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

Abstract

We have studied the incidence angle ( $\theta _{0}$ ) dependence of the sea ice backscattering coefficient ( $\sigma$ °) 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 $\sigma$ ° 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 $\sigma$ ° and $\theta _{0}$ differences of the windows to estimate the slope ${b}_{1}$ (dB/1°) between $\sigma$ ° 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°, respectively, and ${b}_{1}$ for LFYI at HH-polarization was −0.25 dB/1°. 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 $\sigma$ ° 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.