Abstract:
This paper presents a full field technique to invert bottom sound profile and bottom reflectivity from acoustic data collected in shallow water. Bottom sound-speed profile and bottom reflectivity have been traditionally estimated using seismic reflection/refraction when acoustic ray paths and travel time can be identified and measured from the data. Due to the shallow depth in shallow water, the many multipaths due to bottom reflection/refraction make such identification and measurement rather difficult. A full field inversion technique is presented which uses a broadband source and an easily deployable array for bottom sound speed and reflectivity inversion. The technique is a modified matched-field inversion technique referred to as matched beam processing. Matched beam processing uses conventional beamforming processing to transform the field data into the beam domain and correlate that with the replica field also in the beam domain. This allows the analysis to track the acoustic field as a function of incidence/reflected angle and minimize contamination or mismatch due to sidelobe leakage. This technique is illustrated with simulated data for a vertical array and can be generalized to other array configurations, such as a towed array.