Polarimetric characterisation of two layered frozen lakes

Abstract

In terms of radar remote sensing, one of the challenges of future planetary SAR missions will be the estimation of surface, subsurface and upper layer geometric and dielectric characteristics that translate to the localization of subsurface ice and water bodies and could be an indicator for a habitable planet. An example of two-layer structures that appear on earth is frozen lakes. Two layer structures most likely appear in a similar way on other planets as well. For lakes the upper layer consists of ice and the lower one is water. The ice water interface provides high reflectivity for the electromagnetic wave because of the strong dielectric contrast between the two media. Therefore it is a good candidate for evaluating SAR Polarimetric capabilities in subsurface probing. For this L-Band full Polarimetric ALOS(PALSAR) data are used in this research. Previous researches demonstrated the potential of using SAR data for ice monitoring, the growth of ice cover, and freezing to the bottom for shallow Arctic and sub-Arctic lakes in Alaska (Jeffries and Morris, [3]) and northern Canada (Duguay and Lafleur, [2]). The research depends on spatial and temporal variations of the backscattered signal for ice- covered lakes as the mean backscattering from initial ice increases when the ice cover is rather thick for floated ice. Some of the shallow subarctic lakes freeze in winter to the bed forming grounded ice. For those lakes, the mean backscattering from the floated ice decreases as the ice is grounded. With polarimetric observations, frozen lakes can be characterized without the requirement of temporal changes as the polarimetric signature distinguishes clearly ice inhomogeneity influence on the backscattered signal. Further research on modeling the inhomogeneity is required as understanding the influence of different ice structures on the back scattering is essential. [1] Irena Hajnsek: Inversion of Surface Parameters using Polarimetric SAR, Dissertation, DLR Oberpfaffenhofen,(2001). [2] Duguay CR, Pultz TJ, Lafleur PM, Drai D. RADARSAT backscatter characteristics of ice growing on shallow sub-arctic lakes, Churchill, Manitoba, Canada. Hydrological Processes 16: 1631–1644. (2002) [3] Jeffries, M.O., Morris, K. and Kozlenko, N.. Ice characteristics and processes, and remote sensing of frozen rivers and lakes. Remote Sensing in Hydrology, Measuring Environmental Change. Geophysical Monograph 163, C.R. Duguay and A. Pietroniro Editors, American Geophysical Union, Washington, DC. (2005)