INSAR imaging of nearshore wavefield in Monterey Bay

Summary form only given. Interferometric synthetic aperture radar (INSAR) is a relatively new method for imaging ocean surface velocity fields. The basic technique consists of aligning two physically separated antennas located along the radar platform flight path. The signals received at each antenna backscattered from the ocean surface are recorded and processed separately into two complex maps. These two maps are combined interferometrically into a single image. Unlike conventional SAR, which provides a map of covariance of complex reflectivity, the phase of each pixel in the resulting interferogram is directly proportional to the velocity component of the ocean surface in the viewing direction. Two dominant wave systems are clearly seen in the INSAR image. Refraction of a long-fetched background swell system propagating from the southeast with a wavelength of about 400 m (16-s period) is observed. A second wave system with the wavelength of about 130 m (9-s period) was propagating from the northwest. The power spectrum of the surface elevation obtained by simultaneous ground-based measurements exhibits two distinct peaks at the frequencies corresponding to the wave systems observed in the image. The velocity field 2-D wavenumber spectrum was calculated from the INSAR images and compared with the correspondingly adjusted directional frequency spectrum estimated from the shallow water array data. The spectra obtained from viewing the wave field from orthogonal directions provide the full spatial structure of the 2-D wave and current surface velocity field.