Analysis of sea ice surface properties using ASH and Hong approximations in satellite remote sensing

The Hong approximation, an approximation between the vertically and horizontally polarized reflectivities of specular surfaces has been useful for estimating the changes and characteristics produced in sea ice surfaces by climate change. Recently, the direct relationship (Azzam relationship) and the analytical (Azzam-Sohn-Hong (ASH)) approximation were derived and validated between two polarized reflectivities. In this study, the small-scale roughness and refractive index over sea ice are estimated using the ASH and Hong approximations with observations from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E). The ASH approximation is useful to monitor the properties of ice or snow, because those materials have a small value of the imaginary part of the refractive index (<inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="trsl_a_888106_ilm0001.gif"></inline-graphic> ). Meanwhile, the Hong approximation is effective for estimating the melting of sea ice, because the melting of ice or snow indicates the increase in the imaginary part of the refractive index. Consequently, this study suggests that combining ASH and Hong approximations provides an effective procedure for analysing and understanding the melting sea ice surfaces in terms of the small-scale roughness and refractive index.