30 Years of CMTC and CODAR

The year 1978 saw the first of these CMTC meetings, at Newark, DE. At that initial symposium, CODAR was introduced to the current measurement community. The word CODAR had been coined by the author at NOAA two years earlier, to describe a novel HF radar technique that now routinely maps surface currents from hundreds of coastal sites in real time. This presentation describes the CODAR concept and its evolution over the past 30 years. HF radar investigations by this author began in 1967 with large phased array antennas spanning hundreds of meters at the coast. The original operations were done to evaluate its surveillance potential against military targets, including ships. Cost-effectiveness limitations mitigated against the HF radars for military targets. It became immediately obvious, however, that the very strong sea echo could be used to measure currents and monitor sea state. When I joined NOAA in 1972 in order to develop this technology for real-time environmental current mapping, our management and I recognized a major drawback that had to be overcome: the large size and resulting costs of the conventional phased array antennas needed at HF. We solved this by adapting for radar -- for the first time -- direction-finding (DF) rather than beam forming to measure bearing to the target cell. This allowed highly compact, low-cost portable antennas to replace the impractical phased arrays. We reported the very first current maps from HF radar in a 1977 Science paper done with our NOAA compact-antenna CODAR.