Long‐range low frequency shallow water acoustic propagation and bottom penetration experiments for underwater unexploded ordinance.

Abstract

Among the many issues now being explored in the acoustic detection underwater unexploded ordinance (UXO) in shallow water is the impact of propagation and bottom interaction. Here, we report on long range (1 km) propagation measurements in a littoral environment at the sediment‐water interface in the 1 kHz–12 kHz frequency band. The water channel studied was an 8 m deep arm of St. Andrews Bay, Panama City, Florida. The medium grain sandy bottom had a compressional waves peed of 1700 m/s, and the wavespeed in the water was 1539 m/s. A dense array of point pressure measurements (1 cm vertical sampling) were acquired for a synthetic vertical aperture starting from 2 m above and going through 2 m below the interface and at three ranges, 78, 485, and 990 m. The results show deep penetration into the sediment at long ranges for frequencies below 5 kHz. The data are examined using a two‐fluid parabolic equation model, and the overall environmental acoustics are discussed including the nature of sediment penetrat...