Change of sound ray by various equations of the sound velocity in the 621-km propagation experiment

Abstract

Generally, sound velocity used to be calculated according to equations by Wilson (1960), DelGrosso (1974), Chen and Millero (1977), and others, which were obtained by direct measurement in laboratories based on water depth, temperature, and salinity data collected by the XBT (expendable Bathey-tharmograph) or CTD (conductivity temperature depth) system. However, in observations such as ocean acoustic tomography (OAT) where it is necessary to make accurate measurement of the sound wave propagation time over the distance of hundreds to thousands of kilometers, even the slightest difference of the sound velocity can produce significant errors in the observatory accuracy. Thus the effect of various equations of the sound velocity on the formation of the specific sound ray in the SOFAR channel was examined by using the simulation method by the sound ray theory. The simulation results were compared with the specific sound ray data obtained in the 621-km propagation experiment in the northeast Pacific Ocean, and as a result, the equation by Chen and Millero is found to be the most consistent among the three equations.