Assessment on source levels of merchant ships observed in the East China Sea

Abstract

During the past decades, the impact of shipping noise on marine ecology has always attracted more and more interest of the global researchers. Some empirical ship source level models have been proposed. Whether these models can be used to model the underwater radiated noise (URN) of merchant ships transiting near China remains to be examined. The URN of 57 merchant ships was measured with an opportunistic bottom-mounted acoustic observatory in the East China Sea at least one day in each month from Jan. 2015 to Nov. 2016. The propagation losses (PLs) of transiting ships were modeled using Normal Modes combining with the realistic geoacoustic parameters. The corresponding uncertainties were also analyzed, and the bottom type and the source depth were the major factors. Based on PL computations, the Spectral Source Levels (SSLs) of 57 ships were obtained. By comparing with the estimations using empirical models, the discrepancies indicated that the median estimation errors using RANDI-3 model and Ross's model were 0 ( ±7.1) dB and 6.8 ( ±3.2) dB, respectively. Furthermore, the trends with speed and length at different frequency ranges were also compared with Ross's model. These results might be helpful to develop a more precise model for the further research.