Acoustic impact of short-term ocean variability in the Okinawa Trough

The impact of short-term ocean variability on acoustic transmission loss (TL) is examined in the nature run of an observation system simulation experiment (OSSE) centered on the Okinawa Trough in the western North Pacific. Range-dependent examinations of TL in the upper ocean show the impact of variability as it modifies the sonic layer depth and thickness of the surface duct. Short term variations in the marine environment are shown to have potentially significant impact on acoustic propagation, particularly for applications using active sonar. We examine case studies highlighting the effects of three types of phenomena: diurnal warming, typhoon-induced mixing, diurnal warming, and internal waves. These phenomena were identified as important in the OSSE study area during an extensive Navy data collection effort during the summer and fall of 2007. Publically available observations are used to evaluate the fidelity of the nature run, which then serves as the standard for both range-dependent TL computations and comparisons of ocean prediction alternatives. Some of the alternatives do not represent short-term ocean variability. Thus the case studies reveal the types of errors that arise when acoustic calculations fail to account for a sufficient spectrum of environmental influences. TL differences in the variable environments demonstrate acoustic prediction benefits provided by increasingly capable Navy ocean models.