Quantification of Sar Signatures of Shallow Water Ocean Topography.

A hydrodynamic/electromagnetic model has been developed for the purpose of explaining and quantifying SEASAT synthetic aperture radar (SAR) signatures that relate to the bottom topography of the ocean. These bottom topographic features have been observed on SEASAT SAR data of Nantucket Shoals (off Cape Cod, Massachusetts) and the English Channel region of the North Sea. The model uses environmental data (wind, current and depth changes) and radar system parameters (frequency, polarization, incident angle and resolution cell size) as inputs and predicts SAR observed backscatter changes over topographic changes in the ocean floor. The model results compare quite favorably with the actual SEASAT SAR observed backscatter values. The comparisons between the model and the actual data are all within 1.5 dB. This is less than the 2.0 dB required to distinguish between the radar return from two terrain or ocean targets. The developed model is valid for only relatively shallow water areas (i.e., less than 50 meters in depth) and suggests that for bottom features to be visible on SAR imagery, a moderate to high velocity current (0.40 m/s or greater) with a moderate (1-7.5 m/sec) wind-generated sea traveling with some component parallel to the radar look direction must be present. It appears that the SAR observes the topographic features via an increase or decrease in the amplitude of the ocean Bragg wave which is advected by the topographically controlled current.Ph.D.Physical oceanographyUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158912/1/8215082.pd