Acoustic Propagation Uncertainty and Probabilistic Prediction of Sonar System Performance in the Southern East China Sea Continental Shelf and Shelfbreak Environments

The accuracy of any sonar performance prediction depends on the accuracy of its environmental and system-related inputs [e.g., transmission loss (TL), ambient noise (L_N), and target source level (L_S), among others]. However, particularly with the environment, perfect temporal and spatial knowledge of the input is simply unavailable, and as a result, performance prediction is often accomplished using generic input parameters. While this method is often adequate, the uncertainty in the inputs and the effect of this uncertainty on the resulting performance prediction typically remain uncharacterized. A method of accounting for this uncertainty and quantifying the predictive probability of detection (PPD) using probability density functions (pdfs) of TL ( f_c = 900 Hz, Δf = 200 Hz), L_N, and L_S is applied to data collected at two sites in the southern East China Sea northeast of Taiwan during the 2008-2009 Quantifying, Predicting and Exploiting Uncertainty (QPE) Experiment. The first (site A) is located in a relatively flat-bottomed shallow-water (100-110 m) environment 37 km north of the continental shelfbreak, and the second (site B) is located on the 130-m isobath, closer to the continental shelfbreak near the westernmost branch of North Mien Hua Canyon. Uncertainty in measured TL and L_N is quantified, and curves of PPD versus range are presented for both sites. At the time scale of an individual 8-h test event, statistically significant differences in TL were observed over time at both sites. However, longer term averages of several test events spanning up to two years showed little to no difference between the two sites. The greatest source of uncertainty in sonar performance prediction at both sites was found to be that of the ambient noise.