Measurements of Differential Acoustic Travel Times at a Carrier Frequency of 5 kHz in a River Reach at a Range of 1.13 km

We report a simple validation experiment for measurement of “differential travel time” (DTT) between acoustic transducers separated by 1.13 km in a river reach of depth about 7. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$7\mathrm{m}$</tex>. Good correlation is found between the currents estimated from DTT and the cross-sectional bulk velocity, but DTT -based path-averaged current is about 30% greater than cross-sectional average. This difference is probably due to concentration of current velocity toward the vertical plane of the river thalweg, through which the received sound passed.