Comparison of multifrequency phased-array and direction-finding HF radar systems during COPE-3

Several HF radar systems were used to map ocean surface currents in the third Chesapeake Outflow Plume Experiment (COPE-3) conducted just outside the mouth of Chesapeake Bay, off Virginia Beach, VA during October and November 1997. A multifrequency radar system recently constructed by the University of Michigan, an Ocean Surface Current Radar (OSCR) system operated by the University of Miami, and a SeaSonde system developed by Cedar Ocean Sensors, Ltd. All were deployed at nearly the same locations and operated nearly simultaneously. Each of the three systems consisted of two radars separated by about 20 km. Although all three systems are similar in their use of Doppler processing of first-order resonant backscatter of surface-wave HF energy to estimate ocean surface currents, there are significant differences between the systems. The multifrequency system operates simultaneously on four frequencies between 4.8 and 22 MHz and uses omnidirectional transmitting antennas and an array of 8 wideband loop receiving elements operated in either a beam-formation or a direction-finding mode. The use of multiple radar frequencies allows estimates of ocean current to be made at different depths; the effective depth is about 0.04 to 0.08 ocean wavelength, depending on the shape of the vertical current profile. The OSCR system operates on a single frequency and uses a broad-beam transmit antenna and an array of up to 16 whip receiving antennas operated in a beam-formation mode. The SeaSonde operates on a single frequency using an omnidirectional transmit antenna and a set of compact, colocated receiving loops and whip operated in a direction-finding mode