Analyse des interférences acoustiques

Abstract
Lofargrams of underwater acoustic field received on sono buoys often demonstrate interference phenomena due to beating between direct and surface reflected paths. Such deterministic differential phenomenon potentially conveys information on the source-receiver geometry. The direct problem of interference formation has been studied with the PARTAC model. In the general case, many ray-paths link source and receiver (eigen rays). An exhaustive analysis of time delays between the various ray-path families has led to comprehensive graphs. Observability criteria have been used to decipher those graphs to decide which interferences are visible. Solution of the inverse problem, i.e. determining the source-receiver geometry from the interference impulse response and grazing angles structure, has proved uneasy due to measurement difficulties and propagation limitations. Anyway if several rays from the same source can be identified, at least four including bottom returns, it is theoretically possible to determine the source depth and the distance to receiver.