Study of Gulf Stream features with a multi-frequency polarimetric SAR from the space shuttle

The authors use simulations of radar cross-section, based on wave-current interaction calculations, to investigate the origin of a prominent enhancement in L-band, HV polarization radar return that was observed in imagery of the northern boundary of the Gulf Stream (GS) during the first Shuttle Radar Laboratory (SRL-1) mission. The calculations of surface roughness are based on a 1-dimensional surface current model that closely resembles a current convergence that was observed in in-situ current measurements, taken at both sides of the Stream at the time SRL-1 imaged the GS boundary. In agreement with trends observed in the imagery, significant enhancements in L-band HV polarization cross-section occur in the neighborhood of the GS boundary, relative to comparable VV polarization cross-section signatures at X-, C- and L-band. This occurs despite the fact that the magnitude of the L-band HV cross-section is significantly reduced relative to the comparable X-, C-, and L-band VV cross-sections. These results indicate that the associated L-band HV enhancement occurs from tilt-induced modulation in the radar backscatter, which preferentially alters the relative modulation in L-band HV backscatter in regions where considerable variation in surface slope takes place. The authors also provide an overview of a number of additional sub-mesoscale features associated with the Gulf Stream that were present in the image of the GS boundary.