VHF propagation experiment measurement system description

The objective of the VHF propagation experiment was to measure the one-way bistatic reflection coefficient of the ocean versus grazing angle, VHF frequency, polarization and sea conditions. This was accomplished by transmitting RF from a cliff site at Kauai, Hawaii and receiving on an ocean buoy with antennas located near the ocean surface. In order to relate the received signal power (at the buoy) to the reflection coefficient, one had to have an accurate knowledge of the shore transmitted power, shore antenna absolute gain and patterns, buoy antennas absolute gain and patterns, buoy receiver gain, A/D dynamic range, system cable losses, etc. This was a significant challenge. The antenna patterns are required to correct for pattern gain variation as the buoy relates in the water. The rotation is determined by compass readings on the buoy. Tilt, accelerometer, and pressure sensors on the buoy allowed for determination of ocean conditions. The 3 major components of the measurement system used at Kauai were the main ocean (spar) buoy, the meteorological (met) buoy and the cliff-edge shore station equipment. The shore station transmitted the RF signals towards the ocean buoy and communicated to both buoys. The spar buoy received the RF signals from the shore station and transmitted the digitized RF and on-board sensor data back to the shore station. This paper describes the two components that were custom built for the program, the shore station and the spar buoy.