Abstract:

A basin scale underwater acoustic tomography simulation is carried out for the northeast Pacific Ocean to determine the accuracy with which time must be kept at the sources when clocks at the receivers are accurate. A sequential Kalman filter is used to estimate sound-speed perturbation and clock errors. Using an acoustic array of 4 fixed sources and 20 drifting receivers, it is found that the percentage of the modeled ocean's sound-speed variance accounted for with tomography is 92% at 400-km resolution, practically regardless of the accuracy of the clocks. Clocks which drift up to hundreds of seconds of error (or even more) for a year do not degrade tomographic reconstruction of the model ocean. It is shown that tomographic reconstructions of the sound-speed field are insensitive to clock errors primarily because of a wide variety of distances between the receivers and each particular source. Every receiver ``sees'' the same clock error from the source, regardless of section length, but changes of travel time associated with the sound-speed perturbation depend on the section length. The Kalman filter is thus able to reconstruct clock error and to map the sound-speed field accurately. [Work supported by ARPA, #MDA972-931-0004.]