First-Year and Multiyear Sea Ice Incidence Angle Normalization of Dual-Polarized Sentinel-1 SAR Images in the Beaufort Sea

Abstract

Automatic and visual sea ice classification of SAR imagery is impeded by the incidence angle dependence of backscatter intensities. Knowledge of the angular dependence of different ice types is therefore necessary to account for this effect. While consistent estimates exist for HH polarization for different ice types, they are lacking HV polarization data, especially for multiyear sea ice. Here we investigate the incidence angle dependence of smooth and rough/deformed first-year and multiyear ice of different ages for wintertime dual-polarization Sentinel-1 C-band SAR imagery in the Beaufort Sea. Assuming a linear relationship, this dependence is determined using the difference in incidence angle and backscatter intensities from ascending and descending images of the same area. At cross-polarization rough/deformed first-year sea ice shows the strongest angular dependence with −0.11 dB/1 • followed by multiyear sea ice with −0.07 dB/1 • , and old multiyear ice (older than three years) with −0.04 dB/1 • . The noise floor is found to have a strong impact on smooth first-year ice and estimated slopes are therefore not fully reliable. At co-polarization, we obtained slope values of −0.24, −0.20, −0.15, and −0.10 dB/1 • for smooth first-year, rough/deformed first-year, multiyear, and old multiyear sea ice, respectively. Furthermore, we show that imperfect noise correction of the first subswath influences the obtained slopes for multiyear sea ice. We demonstrate that incidence angle normalization should not only be applied to co-polarization but should also be considered for cross-polarization images to minimize intra ice type variation in backscatter intensity throughout the entire image swath.

Classification of Sea Ice Types in Sentinel-1 SAR Data Using Convolutional Neural Networks

“…In several recent studies automated algorithms have been developed for dual-polarization C-band SAR image segmentation and ice/water classification [4][5][6][7][8][9][10]; for retrieval of ice concentration [11,12]; for classification of several ice types [13][14][15]. It is emphasized in these studies that a threshold based classification of ice types on single frequency dual-polarization SAR data is not possible and more advanced methods employing either full polarization, or multi-frequency, or texture analysis are required.…”

SI-STSAR-7: A Large SAR Images Dataset with Spatial and Temporal Information for Classification of Winter Sea Ice in Hudson Bay

“…In this study, referring to the research results of Mäkynen et al [40] and Aldenhoff et al [42], which also studied Sentinel-1 SAR products with EW mode and dual polarization GRD, the incidence angle dependence coefficients for HH polarization and HV polarization were determined to be −0.24 and −0.16 dB/ • , respectively. The central value of the wide incidence angle range was set to 33 • calculated based on our SAR data.…”

“…To compensate for the incidence angle effect, we need to determine the empirical relationships between incidence angle (θ) and the backscattering coefficient (σ 0 ) at HHand HV-polarizations. A lot of research results show that the linear regression model well describes the dependence of σ 0 in dB scale on θ [40][41][42]. Although some researchers expect the incidence angle dependence of radar backscatter to be lower at cross-polarization compared to co-polarization [43], Aldenhoff et al [42] demonstrate that incidence angle normalization should be applied to both co-polarization and cross-polarization images to minimize the variation of backscatter intensity within the same ice type in one image swath.…”

TanDEM-X multiparametric data features in sea ice classification over the Baltic sea

“…Knowledge of the angular dependence of different ice types is necessary to account for automatic sea ice classification of SAR imagery because it is impeded by the incidence angle dependence of backscatter intensities. Several studies at C-band were considering the incidence angle dependence of the sea ice backscattering coefficient (σ°) for different ice types in different polarizations and sea ice conditions (Liu, Guo, and Zhang 2018;Zakhvatkina et al 2013;Aldenhoff et al 2020;Mäkynen et al 2002;Brath, Kern, and Stammer 2013;Gill et al 2015;Onstott 1992;Mäkynen et al 2014).…”

“…One of them is direct slope estimation from backscatter intensity versus incidence angle plots. Another one is, the determination of the σ° versus θ 0 dependence are based on SAR image pairs acquired on ascending and descending orbits over the same sea ice area with a short time difference (Aldenhoff et al 2020) and then incidence angle normalization is regularly applied for various image classification tasks, e.g., (Lang et al 2016;Zakhvatkina et al 2017;Murashkin et al 2018). In the context of this study, the influence of various incidence angles on backscatter intensity in TanDEM-X mission is not possible to assess, as our analysis is based on one image with relatively narrow swath (42.33-44.46).…”