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From August 1989 until August 1990, a simple acoustic telemetry system was used for obtaining real-time data from 5 Inverted Echo Sounders (IESs) deployed in the SYNOP inlet array in the Gulf Stream east of Cape Hatteras. Every 24 hours, each IES calculated a representative travel time from a set of 48 measurements (τ), and telemetered that value to a listening station on Bermuda. From the received data, a daily time series of the depth of the 12oC isotherm (our proxy for main thermocline depth) over each IES was calculated. The position of the Gulf Stream North Wall through the IES array was calculated on a daily basis from the thermocline depth information at each IES site.

The telemetry system is based on encoding data as a time delayed broadcast acoustic signal: the delay of the time of broadcast of the signal, with with respect to a reference time, is proportional to the data value. The changes in delay time, from one broadcast signal to the next, are recorded at a remote receiving station.

The IESs were recovered in August 1990, with the exception of the one at site B2. The telemetered data from the IES at site B2 was, however received at Bermuda. The RMS agreement between thermocline depths, as calculated from the data on tape from the recovered IESs and as calculated from the received telemetry data, is 20 m. This compares favorably with the 19 m uncertainty in calibrating the τs as a measure of the thermocline depth. The RMS agreement between the position of the Gulf Stream path through the IESs as calculated from the tape data and the telemetry data is 5 km.

This telemetry system is not IES specific. It could be used with other appropriately modified oceanographic instruments, such as current meters and pressure sensors.