Analysis of Spotlight Synthetic Aperture Radar Ocean Wave Imagery

During1 the November 1990 SAXON-FPN Experiment, Synthetic Aperture Radlar (SAR) data was collected of ocean waves in the North Sea. The primary objective of this experiment was to investigate SAR imagery of ocean waves at a variety of microwave frequencies under high sea staite conditions. One of the SAR SAXON-FPN wais the P-3/SAR which consists of a three-frequency (X-,C-, and L-band), fully-polarimetric SAR system which is jointly operated by ERIM and the Naval Air Development Center (NADC) and is flown in an NADC P-3 aircraft. instrumented1 tower at several altitudes to collect data which could be used to rigorously evaluate existing SAR ocean wave imaging theories. In addlition to conventional stripmap data, the P-3/SAR collected data at L-balnd in a spotlight mode. Recall that in a stripmap SAR, the antenna pattern illuminates a region perpendicular to the flight path while the forward motion of the aircraft creates the doppler history. In1 the spotlight mode, the radar antenna is continuously repositioned as the aircraft progresses so as to collect data at the same spatial location. For the L-band spotlight mode of the P-3/SAR, the antenna tracks the targeted area over squint angles +45O from broadside and the imaged area on the sea surface is approximately 1 by B km. Spot1 ight data of ocean waves provides several interesting analysis capabilities. directional sensitivity of the wave imaging mechanisms to be studied at a finer scale than conventional stripmap data and without the uncertainties of collecting data at different times. The dwell time over which spotlight data is collected is nominally 60 seconds. this period, the ocean waves propagate into, through, and out of the spotlight scene. wavelengths can be used as a check on water depth. In addition, the longer dwell time allows us to examine both the spatial and temporal frequency of breaking wave events under higher sea states. The results from these analyses and others will be reported in this paper. systems utilized during