Best Practices for SeaSonde Antenna Pattern Measurements

The SeaSonde is one type of High Frequency Radar (HF Radar) which is a coastal ocean current monitoring sensor developed and manufactured by CODAR Ocean Sensors Ltd. HF Radar is a highly efficient, low impact method for generating near real-time surface current velocities. Antenna Pattern Measurements (APMs) are a form of calibration performed on the SeaSonde antenna to attune it to local distortions which impact the bearing determination of the received radio signals. Several methods exist to perform APMs. Those methods include moving a transponder around the antenna by someone carrying it on land or placing the transponder on a boat. Drone patterns are conducted by placing a compact signal source aboard an uncrewed aerial vehicle and performing a similar semicircle around the antennas like the walking or boat pattern. The last method involves using signals from the Automatic Identification System (AIS) to determine the bearing of vessels relative to the radar antenna and using that information to derive the antenna beam pattern. This is accomplished by a radar operator analyzing the output from the AIS method or more recently CODAR has developed artificial intelligence to output an antenna pattern. Each type of APM method comes with its strengths and weaknesses for data quality as well as ease of performance. CODAR recommends the boat pattern whenever possible, but for many HF Radar operators, the APM is a subjective matter and many utilize their preferred methods accessible to them.