Ocean Current Radar Calibration with Ships of Opportunity and the Automatic Identification System Phase I Final Report

We investigate the feasibility of calibrating HF radar systems using HF backscatter from ships along with Automatic Identification System (AIS) broadcasts. We obtained data from 4 SeaSondes, located in the vicinity of the Santa Barbara Channel, with coincident AIS data recorded over 70 days. Using the ship position information from AIS, we identify corresponding ship echoes in SeaSonde HF radar cross spectra, and use this information to reproduce receive antenna patterns over a wide range of bearings. We meet the proposed Phase I objectives as follows: 1) When matched with backscattered signal in cross spectra, the ship positions can be used to accurately reproduce the receive antenna pattern as a function of bearing; 2) Results indicate that accurate antenna patterns can be obtained from as few as 8 individual ships, suggesting that proximity to high volume shipping lanes is not essential; 3) The global scope of the AIS system would allow this method to be used on any of the approximately 350 HF radars in operation world-wide, including all of the IOOS national network sites. The methods presented here are a cost effective way to frequently calibrate HF radar systems. We envision a commercial software product operating on HF radar site computers that integrates data from AIS receivers into the HF radar data processing, producing receive antenna patterns in real time.