SFSU Underwater Acoustics
Research Group

3-Mile Slough Ultrasonic Current Meter
Data of May 3, 1996

The installation at 3-Mile Slough has been collecting data more or less continuously since November 1995. We reported on this data at the Ocean Sciences meeting at San Diego in Feb. 1996. However, the quality of this data is far below the capabilities of the technique.

Coherent detection should measure the current velocity, averaged over the sound path, with mm/sec precision or better. This depends on the psuedo-random phase modulation of the 200-MHz carrier to resolve the modulo-one-period ambiguity which is inherent in any phase-sensitive detection. This isn't working very well right now.

On May 3, 1996, three of us (ANG, MCE, and RWB) went to the Slough to try out a new transducer driver. This driver is a FET switching device which converts the phase-modulated 200 kHz analog signal to a +/- 15 V square wave, with low output impedance. We wanted to see if increasing the signal size made the measurement of current velocity more precise.

Tests Using Stronger Signal

Correlation of Signal Strenth with Envelope Variability