Mr. Tom's Blog

SOFAR receiver at Grand Turk Island

The SOFAR float program took its first steps in 1966 when Henry Stommel introduced me to Doug Webb and learned about his efforts to develop a very low frequency acoustic float that could be heard at great distances. Stommel had already made arrangements for us to use the Broad Ocean Area SOFAR hydrophone network to do the listening. Doug was to develop the float (see ‘A close call in MODE’) and I was was to implement the float tracking system. Compared to Doug’s challenge, my task was rather straightforward. It was to install receiver electronics and digital data recorders, using at first 7-track, later 9-track computer-grade magnetic tape at each of the SOFAR hydrophones. We initially planned to install receivers in Bermuda, Eleuthera, Puerto Rico, and Antigua. But there were issues with the Antigua site (and it was distant) and the Bermuda phone was shadowed toward the west. There was a hydrophone at Grand Turk Island (GTI) but for some reason we couldn’t use it. So, we proposed and received funding from NSF to install our own hydrophone at GTI.

This resulted an impressive installation that Buoy group at WHOI, led by Bob Walden, completed in the fall of 1972. It was a 2-vessel operation. Bob rented a barge from the local government onto which he put the heavy gear. These included the 30,000 ft of armored cable, the two separate 2-element hydrophone arrays, the anchor, the acoustic release, and the steel float that would keep the array vertical. The second boat, the Gulf Stream, from Nova University in Fort Lauderdale, FL, was used to hold position with the outer end of the cable while the barge paid out enough cable so the whole assembly settled on the bottom. Once the mooring (flotation, riser cable, hydrophones, acoustic release, and anchor) was in place the barge continued to pay out cable as it steamed toward the light house at the northern end of GTI. The cable had two layers of torque-compensated armor protecting the electrical conductors with two additional layers of armor for the last section to be laid across the coral reef zone up onto the beach.

Bill Richardson’s group at Nova University built the little hut that would house our equipment. I don’t recall why, but we had to arrange for our own power, so I bought a small diesel generator that proved to be very reliable. The four hydrophones were buoyed at 1200 m depth at the sound velocity minimum (SOFAR channel axis) in 1500 m water. The steel flotation sphere was at 200 m depth. While the system was designed to serve at least 18 months for the 1973 MODE program, it continued to serve us well beyond the polyMODE study in 1978.

Feel free to consult the technical report below for more information. It is a model of how an engineering project should be designed and implemented, the work of first-class professional engineers. This impressive installation was pivotal to the success of the MODE and polyMODE float programs.


Walden, R. G., H. G. Berteaux, and F. Striffler, 1973. The design, logistics and installation of a SOFAR float tracking station at Grand Turk Island, B.W.I. WHOI Technical Report-73-73.