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Mapping Scotland with PALSAR:An Assessment of the Importance of L-Band Polarimetry

Shane Cloude(3), Iain Woodhouse(1), Karin Viergever(1) and Juan Suárez(2)

(1) University of Edinburgh, School of Geosciences (Geography),, EH8 9XP Edinburgh, United Kingdom
(2) Forest Research, Roslin, EH25 9SY Edinburgh, United Kingdom
(3) AEL Consultants, 26 Westfield Avenue, KY15 5AA Cupar, United Kingdom

Abstract

In this paper we present results of using the Quadpol PLR21.5 mode of ALOS-PALSAR for mapping forest and vegetation cover in Scotland. In particular we concentrate on developing new techniques to assess the added information provided by polarimetric modes over simpler dual polarisation configurations. Our objective is to determine quantitative criteria useful for assessing the utility of employing such Quadpol modes in future SAR missions for land observation.

To assess this, we first note that dual channel systems employ only a single polarization parameter, usually a ratio of scattered powers in co and cross-polarized channels, to characterise land cover. For PALSAR for example this is provided by the FBD mode, which employs HH and HV. The conditions under which this is a complete description of terrain scattering can be traced to assumptions of azimuthal symmetry in the plane of polarization. We therefore propose a new test for such symmetry based on a predictive model of the scattering alpha parameter [1]. By comparing the prediction versus estimates taken from the data itself, we then obtain a means of identifying those areas where Quadpol data is adding extra information beyond that provided by dual polarised modes.

To illustrate, we apply the technique to large area mapping of Scotland. This provides a wide variety of interesting land use types, ranging from urban to agricultural, semi-natural vegetation and forestry In particular we address the problems of forest mapping in regions with severe topography, a topic of importance in the context of Scotland’s proposals for future land-use.

[1] S.R. Cloude, E. Pottier, "An Entropy Based Classification Scheme for Land Applications of Polarimetric SAR", IEEE Transactions on Geoscience and Remote Sensing, Vol. 35, No. 1, pp 68-78 , January 1997

 

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