Spatial and temporal coherence of broadband acoustic transmissions in the Straits of Florida

Month-long time series of broadband coherent measurements of channel pulse responses in the Florida Straits allow for estimation of signal coherence under a great variety of signal parameters and environmental conditions. Two 32-element arrays, one vertical and another horizontal (bottomed) along the path of propagation allow for comparison of spatial coherency and single phone temporal coherencies. The transmitted signals cover 5 octaves from 100 through 3200 Hz. Coherencies for single resolved SRBR arrivals are compared with those for unresolved multipath BRB focused arrivals. Many factors are at play including the complication of coherent reception from nearby shipping and multipath interference. However, the time series are long enough to sort out and explain most relations to the environmental variability. Vertical and horizontal coherence lengths are compared over a wide range of frequencies. Generally, SBRB paths are found to be far more stable and coherent than RBR paths especially at higher frequencies suggesting that sound-speed variability near turning RBR rays/modes is more destructive to coherency. The loss of signal coherency for RBR paths is accompanied by a significant loss of signal intensity—as much as 10 to 15 dB.