Reciprocal sound transmission experiments for current measurement in a tidal river

Abstract

Six repeat reciprocal sound transmission experiments for current measurement were successful carried out in the upstream region of the Qiantang River in Hangzhou city, about 90 km from the mouth of Hangzhou Bay during April to December 2009. Two Coastal Acoustic Tomography (CAT) Systems were set up at a distance of 3050 m for making a reciprocal transmission between the both banks of the Qiantang River. During the sound transmission experiments, thirty-two repeat shipboard Acoustic Doppler Profiler (ADP) surveys were also performed along the sound transmission line to get a comparison with the reciprocal sound transmission data. Rangeaveraged current velocities, determined from the travel time differences along the transmission line were in good agreement with those from the ADP, producing a root-mean-square difference of 0.03 m/s .The travel time differences data were well correlated with the river discharge estimated from the ADP data.The time series of river discharge during the experimental period was estimated through an empirical formula, relating to both the parameters. The variations of river discharge caused by tidal bores were well captured. The river discharge changed in the range of -7626 m 3 /s and 5096 m 3 /s, with a mean of 1246 m 3 /s. The above results suggest that the CAT is a powerful instrument for measuring continuously the river discharge in such tidal rivers with quite heavy shipping traffic.

Estimation of currents with acoustic navigation beacons

“…In alternative, the expected direction of the currents can also be taken in consideration. This is the case in the majority of the examples in literature, as for example in [3] or [4], where the reciprocal travel time method is used to predict the currents of rivers, where its direction is easy to predict. On the general case, however, this is not true and the reciprocal method can only be used to establish v c AB , which is the projection of the current v c in the AB direction.…”

A coastal acoustic tomography experiment in the Sanmen Bay, China

“…However, until now only a few of CAT application experiments were carried out outside of Japan [7][8][9][10]. This paper reports the coastal acoustic tomography experiment, which was attempted in the Sanmen Bay near the Taizhou city, China.…”