Feasibility of using standard targets to measure sound attenuation in rivers with varying suspended sediment loads

Abstract

In this study I examined the feasibility of using standard targets to measure sound attenuation in water due to suspended sediment. I determined that the variability of the target strength measurements was sufficiently high to prevent the use of this measure in obtaining accurate attenuation estimates. Average target strength values for a 1.5 inch tungsten carbide sphere differed by as much as 11.4 dB with spreads of the upper and lower 90% values as high as 18 dB. This high variability was likely due to a combination of factors that include multipath signal returns (exacerbated by relatively high transducer side lobes) and inaccuracies in the off-axis correction calculation. Although the goal to determine a relationship between suspended sediment and attenuation was not achieved, theoretical models suggest the contribution of suspended sediment to overall sound attenuation can be significant and, in certain circumstances, the main contributor to overall signal loss.