REVISING VEGETATION SCATTERING THEORIES: ADDING A ROTATED DIHEDRAL DOUBLE BOUNCE SCATTERING TO EXPLAIN CROSS-POLARIMETRIC SAR OBSERVATIONS OVER WETLANDS

摘要

Common vegetation scattering theories indicate thatshort wavelength Synthetic Aperture Radar (SAR)observations (X- and C-band) measure mainlyvegetation canopies as the short-wavelength radar signalinteracts mostly with upper sections of the vegetation.Furthermore, these theories also suggest that SAR crosspolarization(cross-pol) observations reflect onlyvolume scattering. Consequently most SARdecomposition techniques assume that the cross-polsignal represents solely volume scattering. However,short-wavelength and cross-pol observations from theEverglades wetlands, south Florida, suggest that asignificant portion of the SAR signal scatters from thesurface and not only from the upper sections of thevegetation. The indication for surface scattering inwetland environment is derived from phase observableprocessed using interferometric techniques. Theinterferometric SAR (InSAR) observations revealcoherent phase signal in all polarizations and allwavelengths, reflecting water level changes beneath thevegetation. This coherent phase signal cannot beexplained by neither volume scattering nor radar signalinteraction with the upper sections of the vegetations,because canopies and branches are frequently move bywind. The only way that such coherent signal can bemaintained and represents surface water level changes iswhen a multiple bounce from the vegetation and surfaceoccurs. The simplest multi-bounce scatteringmechanism that generate cross-pol signal occurs byrotated dihedrals. Thus, we use the rotated dihedralmechanism to explain the InSAR wetland observationsand to revise the current vegetation scattering theories toaccounts also for double bounce component in cross-polobservations.