Texture Analysis of Polarimetric SAR data
Gianfranco De Grandi(1), Richard Lucas(2), Attilio Gambardella(3) and Maurizio Migliaccio(3)
(1) European Commission, DG Joint Research Centre, Via E. Fermi 2749, 21027, Ispra (VA), Italy
(2) Aberystwyth University, Llandinam Building, Penglais Campus, SY23 3DB Aberystwyth, Wales, United Kingdom
(3) Università di Napoli Parthenope, Centro Direzionale, Isola C4, 80143 - Napoli, Italy
Results reported recently in the literature indicate that texture statistical analysis and radar polarimetry can provide additional information to characterize natural targets in SAR images. As a matter of fact, spatial variations of SAR backscatter bear information on structural and geometric properties of natural targets, and therefore can be potentially useful for deriving biophysical parameters, or for classification problems. These variations and their relationships are visually perceived as image texture, and can be measured by the statistics of some underlying random process.
The Wavelet Polarization Signature (WASP)  is a formalism for analyzing in SAR imagery the dependences of texture measures afforded by wavelet frames on scale and polarization state. In detail, WASP encapsulates in graphical form the dependencies of texture measures on polarization and scale. These measures are a proxy of the structure function statistics. As such, they are related to the autocorrelation function for stationary processes, and to the fractal dimension for non-stationary processes with stationary increments.
Based on this theoretical background, two experiments are reported where wavelet WASP analysis is applied to SAR observations of natural targets, both in the land and marine domains. The objective is to assess the potential usefulness of the technique in different thematic contexts and to validate experimentally the effects predicted by theory. The first experiment is thematically oriented to tropical forest mapping and illustrates how spatial properties of the classes of interest (swamp forest, lowland rain forest and secondary forest) are reflected in WASP analysis in a mixture of texture strength and polarimetric diversity. The second experiment is in the marine domain, and concerns the characterization through WASP analysis of oil spills, biogenic lookalike, and sea clutter under different wind conditions. Analysis conducted so far indicates that texture measures based on wavelet frames can be an effective vehicle to characterize the spatial statistics of SAR observations in the combined space-scale-polarization domain.
 De Grandi G., Lee J.S., Schuler D.L., "Target Detection and Texture Segmentation in Polarimetric SAR Images Using a Wavelet Frame: Theoretical Aspects", IEEE Trans. Geosci. and Remote Sensing, vol. 45, no. 11, pp. 3437-3453, November 2007.