Numerical prediction of coherent integration time at 75 Hz, 0.03 temporal resolution at 3250 km

Coherence time of sound is modeled for a 3250 km section in the Pacific at 75 Hz, 0.03 s resolution between a source and receiver both moored high above the ocean floor. The model is based on the temporal evolution of a standard spectrum of internal gravity waves and an accurate approximation for the acoustic wave equation. The probability is 0.6 that the signal-to-noise (s/n) ratio first decreases at times of 13 min or less. Afterward, the s/n usually increases, reaching a peak near 40 min. This is longer than the experimentally reported coherence time of 12.7 min. The discrepancy could be due to the fact that the experimental value was obtained assuming that movement between the source and receiver could be accounted for using a single Doppler speed correction for each transmission lasting between 10 and 40 min. However, accelerations of the source and receiver appear to be too large to use the single Doppler speed correction. Coherence times from the data should be re-analyzed with a variable Doppler scheme to see if they are consistent with the 40 min coherence time predicted from the model