Abstract
Seasonal frozen ground and snow cover are sensitive indicators of how our home planet is changing. In the meantime, new spaceborne SAR systems have been launched, such as the polarimetric PALSAR sensor on-board ALOS in January 2006. In this paper, the relevance of L-band polarimetric SAR data for extracting cryospheric information is presented over lowlands. It is first demonstrated that dry snowpack over frozen ground slightly affects the polarimetric signature. Given the fact that PALSAR data do not enable the use of a simplistic threshold-based method, a refined method for snow detection in PALSAR time series is outlined. A supervised Support Vector Machine is used showing fairly good results within the framework of a three-class classification (dry snow over frozen ground, wet snow and free of snow). Beyond these qualitative studies, a polarimetric EM backscattering model over snow-covered frozen fields brings out the possibility for quantitative assessments. The residual liquid water content in frozen ground over lowlands is estimated from PALSAR measurements.
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Notes
- 1.
The entropy determines the degree of randomness of the scattering process, the \(\bar \alpha\) angle is related to the physics behind the scattering process (\(\bar \alpha \to 0\): single-bounce, \(\bar \alpha \to \pi /4\): volume, \(\bar \alpha \to \pi /2\): double-bounce). The anisotropy A measures the relative importance of the second and the third eigenvalues of the eigen decomposition.
- 2.
k-fold cross-validation consists in partitioning the data set into k subsets. Of the k subsets, k – 1 subsets are used as training data, and the remaining single subset is retained as the validation data for testing the hyperplane. The cross-validation process is then repeated k times, with each of the k subsets used exactly once as validation data. Finally, the k results are averaged producing a single and stable estimation.
- 3.
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Acknowledgments
The authors greatly acknowledge the Japan Society for the Promotion of Sciences (JSPS) for providing financial support from October 2007 to September 2008 through its short-term fellowship program. The authors would like to thank A. Hachikubo, T. Tanikawa (Kitami Institute of Technology, Japan) and Y. Miyagi (EORC/JAXA) for their help and support during the snow campaign held on February 2008.
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Longépé, N., Shimada, M., Allain, S., Pottier, E. (2010). Extracting Cryospheric Information over Lowlands from L-Band Polarimetric SAR Data. In: Chuvieco, E., Li, J., Yang, X. (eds) Advances in Earth Observation of Global Change. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-9085-0_7
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