Abstract:
A shallow water, high-frequency active acoustic data set is being examined for the existence of a broadband frequency dispersion phenomena (BDP). Two scenarios, an up-slope source-to-receiver propagation path and a shallow-to-shallow path are studied in detail using a time domain finite element parabolic equation model and measured environmental parameters. It was expected that the analysis of the shot data from the AEAS exercise off the Pacific West Coast would result in confirmation that echoes or reflection events from bottom reflectors would be distinguishable from echoes of water column reflectors. This expected result could be detected only for the up-slope propagation path where energy spreading loss (ESL) was relatively low. The shallow-to-shallow propagation paths were dominated by ESL and it was determined that the ESL must be modeled accurately before the BDP can be analyzed and utilized for very shallow water propagation paths. ESL is modeled for the two propagation scenarios and the impact of ESL on active high-frequency operations in very shallow water is discussed. Signal processing solutions to ESL degradation are also presented. [This work was funded by the Office of Naval Research.]