Broadband interference patterns in shallow water

Abstract

While measuring ship‐radiated noise levels in the Inland Sea of Japan, broadband interference patterns were observed for ranges less than 1500 m. The water depth was 42 m with little bottom relief. The water column was well mixed with practically no thermocline. The sea state was nearly calm. For these conditions interference patterns could be observed at acoustic frequencies of 200–2000 Hz, which varied with source‐receiver geometry. A ray‐tracing program was developed to explain these patterns assuming no acoustic refraction and a simplified bottom loss algorithm. In addition to the Lloyd mirror effect, the patterns were reconstructed from those paths which encountered one bottom reflection. The reconstructed patterns have intensity variations, frequency dependence, and range dependence quite similar to the observed data.