Broadband matched field processing (MFP)-derived estimates of 3D source location using data from hydrophone line arrays deployed in various geometries, i.e., vertical, horizontal, and tilted 45° from vertical, are presented in this paper. These data were collected in two shallow water (100–200 m) experiments off the coast of San Diego. Results show that estimates of source range and depth remain surprisingly coherent in the presence of large mismatch in bathymetry, but are offset from the true position by as much as 100%. The offsets are independent of array geometry. In contrast, for estimates of source azimuth, bathymetry mismatch typically causes a degradation in MFP correlation rather than an appreciable offset. However, errors in the assumed tilt from vertical of an array can lead to large offsets in the estimated source azimuth, particularly as the nominal angle of the array from vertical becomes smaller. Predictions from a simple analytical model based on adiabatic normal modes in ideal waveguides provide good fits to the broadband MFP results.

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Broadband (50–200 Hz) matched field processing was performed on vertical line array data from a recent shallow water experiment. Although the actual water depth steadily decreased from 200 to 100 m over the source tow track, the replica vectors were calculated assuming a range-independent environment of 200 m depth. Rather than breaking up due to the increasingly severe environmental mismatch, the broadband matched field output peak in range and depth behaved in a consistent way; both the predicted range and depth of the source became increasingly greater than its true range and depth as the true water depth decreased. A simple analytical model was developed to predict the behavior of these MFP mirages. The good agreement between model predictions and actual results suggests that the model can be used to quantify the impact of unknown water depth changes (e.g., ocean swell on synthetic aperture studies) and to ‘‘calibrate’’ water depth in a region using the sinking mirages of surface ships of opportunity. By use of the concept of ‘‘effective depth’’ developed by D. E. Weston et al., the model also can be applied to studies of ocean bottom geoacoustic parameter mismatch. [Work supported by ONR, code 321.]

Detailed seafloor environmental modeling of a moderately complex shallow water area, coupled with multitone matched-field processing, produced reliable and unambiguous source detection and tracking. Frequency averaging of the matched-field output sufficiently reduced sidelobe ambiguities. The seabed geologic model is a gridded database containing water depth, sediment grain size, sediment thickness, and acoustic basement type. Grid cells are squares of side length equal to 2 arc s. Software, separate from the geologic model, computes a geoacoustic model for any desired grid square.