Measurements of Coastal Currents Using a Ship Based VHF Radar System

摘要

The University of Miami Ocean Surface Current Radar (OSCR) is a pulsed radarwhich utilizes a Yagi transmit antenna and a phased, line array receive antenna. In its VHF (50 MHz) mode of operation, the system has a range of 12 km and a resolution of 250 m. The Bragg resonant wavelength is 3 m. In December 1993, one of two OSCR VHF sites was configured aboard the 50 m research vessel COLUMBUS ISELIN, anchored in a four-point mooring 5 km from the second site on Key Biscayne, FL. A six channel accelerometer system was used to obtain ship motion measurements. The purpose of this experiment was an initial evaluation of using an OSCR type system to map nearshore coastal currents from a ship. Our results show that high quality vector current maps can be obtained provided that the motions of the support platform are moderately restrained and that the system is mounted so as to avoid superstructure effects. During our experiment, we have also shown the validity of these maps through comparisons with shore based measurements, known tidal flows and drifter observations. The capability to deploy an OSCR type system offshore leads to the potential for wide area, long term, real time monitoring of nearshore coastal currents. This potential would be useful in many coastal survey operations. The capability also leads to the potential for rapid change in the area of coverage via moving the locations of the support platforms. This potential would be useful in predicting the trajectories of nearshore spills of oil and other hazardous materials. VHF Radar, Surface currents, Coastal currents, Radar backscatter, Remote sensing.