From the Desk of Don Barrick
Company President reflects on how CODAR technology evolved from conventional HF radar
In the late 1960s, the Defense Department became intrigued by coastal HF radar, eager to exploit the conducting sea
surface which allowed coverage well beyond the visible horizon. During this period I was technical director for several
DARPA programs aimed at seeing ships, aircraft, missiles, and wakes.
Several large companies (like Raytheon) built massive phased-array antennas to demonstrate military beyond- the-horizon
surveillance capability. Indeed, they all saw hard targets. But based on the size and cost, the militaries at that time decided
they were not cost-effective for operational use. You see, conventional target bearing determination says that you need an
antenna tens of wavelengths across to form and scan a narrow beam.
A flashlight is one example. A scanning 1-m dish is the
microwave radar equivalent, where wavelength is 3 cm. Scaling down to HF where wavelength might be 30 m leads to an
antenna aperture that is 1000 m long (yes, that's 1 km), far to big to rotate mechanically. But with this approach, building an
array and carefully phasing its signals electronically does allow one to form and scan a narrow beam.
In the meantime, I noticed in the signal spectrum data a consistent presence of two strong peaks on either side of the zero
Doppler. I derived mathematically, and then field-validated in 1972 using the radar on California’s San Clemente Island, that
these two strong signals far above background noise floor were the backscatter off ocean waves half the radar transmit
wavelength: one exhibiting positive Doppler from waves approaching shore and other negative Doppler from those waves
traveling away from shore. These echoes were considerably stronger than noise floor due to fact they were adding coherently
as they made their way back to the receiver at shore and which I dubbed as “Bragg echoes”. This commemorated Sir Bragg
who 100 years earlier discovered the nature of crystals by probing with x-rays by the same diffraction-grating method. Given
the fact these Bragg echoes were virtually omnipresent I was inspired to explore how HF radar could be used for
environmental (currents, waves) rather than military (hard target) ocean applications.
NOAA hired me to develop this environmental measurement capability as the agency was being formed in 1972.
The first strong nudge I got from higher up was: "Don, we want to use this widely, but with antennas like that,
we're dead in the water. If you want funding to develop this, it must be practical, small size, low cost." So I came up with the
artist sketch of a compact antenna concept and asked "How about something like this"? And so we headed off in that
direction. From this point, we called it CODAR, initially for Coastal Ocean Dynamics Applications Radar (and today
CODAR acronym more widely denotes Compact Radar, and also our company name).
My team inside NOAA grew to about 25, with a dozen or more tests to validate its capability and utility, and earning the
Department of Commerce’s distinguished Gold Medal of Excellence award. At the urging of NOAA, it became time to leave
government with my key people for transitioning into a commercialized version, and hence in 1986 CODAR Ocean Sensors,
Ltd. was born. Our first product was the SeaSonde®, with the compact single-mast antenna that did not differ conceptually
from what I proposed in 1972.
Today NOAA is an important user of SeaSonde which constitutes approx. 90% of their Integrated Ocean Observing System
(U.S. IOOS) National HF Radar Network. This compact radar has also been adopted in approximately 30 other countries and
is the technology of choice for large-scale national observing networks.
HF phased array antenna 500 m long I built in 1971 for military surveillance
on San Clemente Island, CA. Equipment and phasing cabling were housed
in four trailers, weighing about 50 tons. Output power was about 25 kW
peak, or 500 W average.
|My conceptual drawing of compact CODAR antenna
in 1972 at NOAA.