Remote Sensing of Desert Dune Forms by Polarimetric Synthetic Aperture Radar (SAR)

This report describes remote sensing experiments using highly capable polarimetric synthetic aperture radar (SAR). In preparation for the launch of the SIR-C/X-SAR mission, NASA’s JPL airborne polarimetric SAR (AIRSAR) was deployed over many locations worldwide. The report describes SAR observations of desert dune fields in North America, Bolivia, and Australia acquired by AIRSAR and in Namibia acquired by SIR-C/X-SAR. The use of polarimetric and multiwavelength SAR is reviewed and comments on the advantages of the various combinations are noted. SAR data are very useful in mapping dunes because of the ability to control illumination parameters such as look angle, wavelength, and polarization. Furthermore, the unique responses of SAR to surface roughness are found very useful in mapping dune forms. For most sites, the longer wavelengths, P- and L-band at λ=68 cm and 24 cm, are advantageous over the shorter (C-band at λ=5.6 cm) providing better contrast. Overall, copolarized channels (HH and VV) are found best for mapping the dunes and dune types. When trying to discriminate active from inactive dunes cross-polarized channels provide essential information on vegetation.