RIASSUNTO
Real-time monitoring of spatiotemporal wave-current fields along busy ferry routes have been strongly required in maritime disaster prevention, including ship accidents. Coastal acoustic tomography (CAT) systems have been frequently applied to various straits, proposed and developed to monitor current fields. In this study, to realize real-time monitoring of strong current fields in a ferry route at the northern part of Bali Strait in Indonesia, a CAT experiment with four acoustic-stations was conducted. The spatiotemporal current fields were successfully reconstructed by the inversion of reciprocal sound transmission data. The north-south ward current was dominants and strongly vortex generated at the Java side.
INTRODUCTIONBackground
The shipping industry has always been supporting global and local trades, as well as transportation. The growth of shipping activities enhanced the concern of ship accidents due to those destructive impacts corresponding to fatalities, economic losses, various environmental damages and contaminations. Many ship accidents caused by severe sea states such as varying strong current. The spatiotemporal wave-current fields on the busy shipping routes, including ferry routes, could be useful to reduce the ship accidents. In addition, use of favorable ocean currents from a fine-resolution ocean currents can reduce the fuel consumptions (IMO, 2011). By avoiding the opposite currents and take advantage of ocean currents, the relative average fuel savings could be estimated (Lo and McCord, 1995).
Since it is always prohibited to operate shipboard and moored acoustic Doppler current profilers (ADCPs) around ferry routes, a new approach is required to measure the temporal variation of current fields. Coastal acoustic tomography (CAT) system which has been proposed as a coastal-sea application of ocean acoustic tomography (OAT) is a prosperous candidate of the new method. Current structures in the coastal seas can be measured continuously around ports, bays, straits, and inland seas without disturbing the shipping activities, ferry boat transportation, fishery activities, and marine aquaculture industries (Kaneko, et al., 1994; Park and Kaneko, 2000; Zhu, et al., 2012). The accuracy of CAT data has already been adequately validated with ADCP and conductivity, temperature, and depth (CTD) data which attempted in coastal seas around Japan (Yamaoka, et al., 2002; Yamaguchi, et al., 2005; Zhang, et al., 2015) and China (Zhang, et al., 2017).