Ku-, X- and C-Band Microwave Backscatter Indices from Saline Snow Covers on Arctic First-Year Sea Ice
Ku-, X- and C-Band Microwave Backscatter Indices from Saline Snow Covers on Arctic First-Year Sea Ice
复制标题
北极第一年海冰上的盐雪覆盖的 Ku、X 和 C 波段微波后向散射指数
作者：
V. Nandan;T. Geldsetzer;Mallik S. Mahmud;J. Yackel;S. Ramjan
在这项研究中，我们比较了Ku波段、X波段和C波段的微波后向散射，它们来自14 cm、8 cm和4 cm的盐分覆盖在光滑的第一年的海冰上。使用Ku、X和C波段地面偏振微波散射计系统测量了三个雪盖的全极化后向散射，与相应的现场雪热物理测量结果基本一致。这项研究调查了来自散射计系统的共极化后向散射观测在所有三个频率上的差异，对穿透深度进行了建模，利用共极比，并引入了双频率比来区分这些雪盖中主要的偏振相关频率。结果表明，由于积雪较薄，积雪盐度梯度较大，三个频率下测得的共极化后向散射值均随着积雪厚度的减小而增大。创新的双频比率表明，随着积雪厚度的增加，Ku波段微波对雪粒尺寸的敏感度增加，而X波段微波对积雪盐度的变化随着积雪厚度的减少而变化。C波段对积雪盐度变化的敏感度最低。我们的结果表明，盐度相关的介质损耗的影响，贯穿于三个雪盖的所有层，作为影响微波后向散射和穿透所有三个频率的控制因素。我们使用共极化后向散射、共极比和双频率比进行的“地块尺度”观测表明，未来有可能将我们的多频率办法扩大到“卫星尺度”办法，以便有效地开发第一年光滑海冰上的雪地球物理和热力学反演算法。
In this study, we inter-compared 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 Ku-, X- and C-band surface-borne polarimetric microwave scatterometer system was used to measure fully-polarimetric backscatter from the three snow covers, near-coincident with corresponding in situ snow thermophysical measurements. The study investigated differences in co-polarized backscatter observations from the scatterometer system for all three frequencies, modeled penetration depths, utilized co-pol ratios, and introduced dual-frequency ratios to discriminate dominant polarization-dependent frequencies from these snow covers. Results demonstrate that the measured co-polarized backscatter magnitude increased with decreasing snow thickness for all three frequencies, owing to stronger gradients in snow salinity within thinner snow covers. The innovative dual-frequency ratios suggest greater sensitivity of Ku-band microwaves to snow grain size as snow thickness increases and X-band microwaves to snow salinity changes as snow thickness decreases. C-band demonstrated minimal sensitivity to changes in snow salinities. Our results demonstrate the influence of salinity associated dielectric loss, throughout all layers of the three snow covers, as the governing factor affecting microwave backscatter and penetration from all three frequencies. Our “plot-scale” observations using co-polarized backscatter, co-pol ratios and dual-frequency ratios suggest the future potential to up-scale our multi-frequency approach to a “satellite-scale” approach, towards effective development of snow geophysical and thermodynamic retrieval algorithms on smooth first-year sea ice.