Assessment of RISAT-1 and Radarsat-2 for Sea Ice Observations from a Hybrid-Polarity Perspective

Abstract

Utilizing several Synthetic Aperture Radar (SAR) missions will provide a data set with higher temporal resolution. It is of great importance to understand the difference between various available sensors and polarization modes and to consider how to homogenize the data sets for a following combined analysis. In this study, a uniform and consistent analysis across different SAR missions is carried out. Three pairs of overlapping hybrid-and full-polarimetric C-band SAR scenes from the Radar Imaging Satellite-1 (RISAT-1) and Radarsat-2 satellites are used. The overlapping Radarsat-2 and RISAT-1 scenes are taken close in time, with a relatively similar incidence angle covering sea ice in the Fram Strait and Northeast Greenland in September 2015. The main objective of this study is to identify the similarities and dissimilarities between a simulated and a real hybrid-polarity (HP) SAR system. The similarities and dissimilarities between the two sensors are evaluated using 13 HP features. The results indicate a similar separability between the sea ice types identified within the real HP system in RISAT-1 and the simulated HP system from Radarsat-2. The HP features that are sensitive to surface scattering and depolarization due to volume scattering showed great potential for separating various sea ice types. A subset of features (the second parameter in the Stokes vector, the ratio between the HP intensity coefficients, and the α s angle) were affected by the non-circularity property of the transmitted wave in the simulated HP system across all the scene pairs. Overall, the best features, showing high separability between various sea ice types and which are invariant to the non-circularity property of the transmitted wave, are the intensity coefficients from the right-hand circular transmit and the linear horizontal receive channel and the right-hand circular on both the transmit and the receive channel, and the first parameter in the Stokes vector.

Assessment of the High Resolution SAR Mode of the RADARSAT Constellation Mission for First Year Ice and Multiyear Ice Characterization

“…We note that in our study the σ 0 RV and σ 0 RH backscattering from FYI is much lower than the reported in [26]. The difference in FYI backscattering between the two studies should be related to the different environmental conditions, where in our study smooth thick FYI in dry winter conditions is investigated while in [26] wet or covered with fresh snow layer FYI was investigated during the melt season. Most of the FYI and MYI histograms in the investigated CP parameters do not conform to the normal distribution ( Figure 3).…”

“…Results of this study showed that the second element of the Stokes vector, the right co-polarized ratio and the α s angle are three CP parameters that can be affected by a possible non-circularity of the transmitted radar signal from a CP SAR system. On the other hand, [26] found that the first element of the Stokes vector and the σ 0 RH (right-circular transmit and linear horizontal receive) and σ 0 RR (right-circular transmit and receive) backscattering coefficients are the best CP parameters for the separability between various sea ice types. These findings are also consistent with those reported earlier in [4] for simulated CP data, but for dry ice winter conditions.…”

“…In [25], a comparison of the CP results with those obtained by spatially and temporally near-coincident RADARSAT-2 FP SAR data indicated promising results of the CP SAR configuration for sea ice observation. In another study [26], a set of CP parameters extracted from RISAT-1 CP SAR data were compared with CP parameters extracted from simulated CP SAR data obtained using near collocated RADARSAT-2 FP SAR imagery over seasonal sea ice during the melt season. This study was the first to investigate the possible effect of the non-perfectly circular RISAT-1 signal on the discrimination between sea ice types.…”

Hybrid Dual-Polarization Synthetic Aperture Radar

“…Ponnurangam showed that, for soil moisture applications, HCP "works well" [59], and Uppala [60] found that compact polarimetry "works well" for maize crop discrimination. Espeseth et al [61] achieved "similar results" when comparing classifications derived from RISAT-1 HCP data and HCP data emulated from Radarsat-2 for sea ice applications. Kumar et al [62] applied unsupervised model-based classification techniques on the Stokes parameters from the RISAT-1 HCP mode to yield "very good" results.…”

Mid-season Crop Classification Using Dual-, Compact-, and Full-Polarization in Preparation for the Radarsat Constellation Mission (RCM)

“…Relative phase (δ) ranges between −180 • and 180 • [12] and indicates that whether the surface (δ > 0) or double-bounce (δ < 0) scattering is dominant [27]. Similar to the alpha angle of Cloude-Pottier decomposition, Cloud α s [28] characterizes dominant scattering mechanism [29].…”