Wide-angle reflection measurements (TREX13): Evidence of strong seabed lateral heterogeneity at two scales

Abstract

Broadband wide-angle reflection data possess high information content, yielding both depth and frequency dependence of sediment wave velocities, attenuations, and density. Measurements at two locations off Panama City, FL (TREX13), however, presented a surprise: over the measurement aperture (a few tens of meters) the sediment was strongly laterally variable. This prevented the usual analysis in terms of depth dependent geoacoustic properties. Only rough estimates could be made. On the other hand, the data provide clear evidence of lateral heterogeneity at O(100-101) m scale. The two sites were separated by ~6 km, one on a ridge (lateral dimension 102 m) and one in a swale of comparable dimension; the respective sound speeds are roughly 1680 m/s and 1585 m/s. The lateral variability, especially at the 1–10 m scale is expected to impact both propagation and reverberation. Characteristics of the reflection data and its attendant “surprise” suggest the possibility of objectively separating the intermingled angle and range dependence; this would open the door to detailed geoacoustic estimation in areas of strong lateral variability. [Research supported by ONR Ocean Acoustics.]