Jagvijay P. S. Gill

Evaluation of C-band SAR polarimetric parameters for discrimination of first-year sea ice types

In this study, the classification potential of polarimetric parameters derived after Cloude–Pottier decomposition, Touzi decomposition, Freeman–Durden decomposition, normalized radar cross section measurements, phase differences, and statistical synthetic aperture radar correlation measures is evaluated by relating them to three pre-identified sea ice types and wind-roughened open water. A combined approach that constitutes a visual inspection of estimated probability densities of the polarimetric parameters and quantitative analysis using supervised classifications (k means and maximum likelihood) is adopted. Polarimetric parameters are iteratively combined in pairs and triplets to test for their ice type discrimination potential. Sensitivity of polarimetric parameters to radar incidence angle is also examined. Our results demonstrated strong but variable sensitivity of polarimetric parameters to different ice types, which was dependent on radar incidence angle. Results of parameter evaluation demonstrated that no single parameter discriminates significantly (>60%) between all the ice types considered in the study. Combining two low correlated parameters increased the classification accuracy by 10%–22%. Combining the third polarimetric parameter did not necessarily improve the classification results. However, the best classification results were achieved using a combination of three parameters.

Analysis of consistency in first-year sea ice classification potential of C-band SAR polarimetric parameters

The consistency in first-year sea ice classification potential of C-band SAR polarimetric parameters was analyzed by comparing the results of two studies conducted for the same ice types under different geophysical settings. The SAR images used in the comparison were acquired at an incidence angle difference of 4°. Probability density functions, grey level parameter images, and classification statistics derived using k-means classifier were used in the comparative analysis. The investigation showed that not all polarimetric parameters exhibit consistency in their classification performance under different geophysical settings. Out of the 20 polarimetric parameters analyzed, 12 demonstrated high levels of classification consistency between the two studies. Among these 12 parameters, only four possessed high classification accuracy and could be applicable for sea ice classification under variable environmental conditions. The parameters that showed the highest classification accuracies in both the studies were found to be inconsistent in their ice type separation capabilities. The signatures of these parameters differed for one or more ice types when compared between the two studies. The utility of these parameters in individual sea ice classification studies is recommended but their relevance in generalized sea ice classification scheme is unclear.

Multi-frequency microwave backscatter indices from saline snow covers on smooth first-year sea ice

This study inter-compares observed Ku-, X- and C-band microwave backscatter from saline 14 cm, 8 cm, and 4 cm snow covers on smooth first-year sea ice. A surface-borne multi-frequency (Ku-, X- and C-bands) polarimetric microwave scatterometer system is used near-coincident with in situ snow geophysical measurements. The study investigated differences in scatterometer observations for all three frequencies, co-pol ratios, and introduced new dual-frequency ratios to discriminate dominant polarization-dependent frequencies from these snow covers. Preliminary results suggest that, thinnest 4 cm snow cover demonstrate greatest increase in microwave backscatter from all three frequencies, followed by backscatter from thicker 8 cm and 14 cm snow covers. Dual-frequency indices derived for all frequency and polarization combinations suggest greater sensitivity of Ku-band microwaves to snow grain microstructure with increasing snow thicknesses, X-band microwaves to changes in snow salinities with decreasing snow thicknesses. Our results indicate the effect of dielectric loss associated with high salinities throughout all layers of the three snow covers, as the dominant factor affecting microwave penetration and backscatter from all three frequencies.

Diurnal Scale Controls on C-Band Microwave Backscatter From Snow-Covered First-Year Sea Ice During the Transition From Late Winter to Early Melt

Diurnal observations of coincident in situ physical-, electrical-, and surface-based C-band microwave scattering properties of a 16-cm saline snow cover on smooth, moderately saline, first-year sea ice are presented for the transition period between late winter and early melt. Statistical regression analysis and backscatter modeling are employed to explore the scattering mechanisms within the snowpack and to assess associations between backscatter and snow properties for both periods. Our results demonstrate substantial variation in both measured snow properties and C-band microwave backscatter over the diurnal cycle during the late winter period when the difference between maximum and minimum air and snow surface temperature was approximately 5 °C. No such variation in snow properties and backscatter occurred for the early melt period when our case study exhibited a small diurnal variation (~1°C) in air and snow surface temperature. Statistical and modeled results show significant association between the microwave backscatter and snow properties for the top 8 cm of the snowpack. Basal snow properties do not contribute toward total backscatter in either case. As a result, we are certain that the sea ice surface was a negligible scattering interface during both cases. Correlations between backscatter and snow properties are incidence angle dependent, demonstrating the highest association at 50°. Diurnal backscatter from RADARSAT-2 synthetic aperture radar acquisitions support the influence of varying diurnal snow properties on C-band backscatter, showing a difference of ~4 dB for

Multi-frequency polarimetric microwave observations of snow cover on first-year Arctic sea ice

{ \sigma }_{\vphantom {R_{j}}{\text {hh}}}^{o}

Sensitivity of C-band synthetic aperture radar polarimetric parameters to snow thickness over landfast smooth first-year sea ice

and

C-band backscatter from a complexly-layered snow cover on first-year sea ice

{ \sigma }_{{\text {vv}}}^{o}

Ku-, X- and C-band measured and modeled microwave backscatter from a highly saline snow cover on first-year sea ice

during the late winter period. This difference is reduced to <1 dB for the early melt period.

Comparison of a coupled snow thermodynamic and radiative transfer model with in situ active microwave signatures of snow-covered smooth first-year sea ice

This study explores the potential of a multi-frequency (Ku-, X- and C-band) scatterometry approach, to understand microwave interactions between teo statistically different snow thickness covers (14cm and 8cm) on first-year Arctic sea ice during the late winter to early-melt season transition. The results show substantial differences in backscatter response from all three frequencies, for both snow covers. Highly-saline snow covers with fluctuating snow geophysical and thermodynamic properties cause these backscatter fluctuations, with contributions from surface and volume scattering from different snow layers and interfaces. C-band exhibited drastic variations in backscatter, especially for the 14cm snow cover, when compared to Ku- and X-band. In the case of 8cm snow cover, all the three frequencies show minimal sensitivity to snow electro-thermo-physical properties. Our results show distinctly different snow thermodynamic processes operating within the different snow layers, essential for snow thickness estimation on first-year sea ice using active microwave remote sensing approaches.