Acoustic reciprocal transmission experiments, Florida Straits

Abstract

An acoustic approach for the measurement of range- and depth-averaged current and temperature is successfully demonstrated for the bottom-limited acoustic transmission of the Florida Straits. The shallow water environment prohibits the use of deep ocean tomography methods since there are usually no separable arrivals associated with eigenrays. Instead, multipath groupings of arrivals are shown to have stable envelopes if averaged sufficiently long to eliminate effects of interference. The shape of the envelope is controlled to some extent by the source–receiver depth and has characteristics which can be used for very precise travel time measurements. Ray models predict a unique relation between ray height above the bottom and arrival time allowing for unambiguous inversion. Two three-point reciprocal transmission experiments were conducted in the Florida Straits (ranges approx. 25 and 45 km). Two-way channel pulse responses are analyzed to give travel times which are then inverted to give depth averages of temperature and current; the depth and extent of the average is determined by ray models. The method is shown to be precise in resolving variations in temperature of 0.002 °C and current of 2 cm/s. The spatially averaged tomographic results are compared with point measurements of current and temperature from current meter moorings along the path of propagation.