Source localization in range and depth in an Arctic environment

A fixed cw source in the Central Arctic was accurately localized in range and depth using wave-based full-field ambiguity function techniques. The data were taken during the Fram IV experiment, utilizing a vertical array spanning the upper 960 m of a deep-water environment (generally greater than 2800 m) and a high SNR signal from a 20-Hz source at a distance of 270 km from the array, both suspended from the ice cover. The predicted field was computed using a fast field program. Both a linear correlation of the predicted field with the received field and a maximum likelihood method (MLM) estimator correctly localized the source. The MLM estimator produced sidelobes significantly below the main peak, while the linear correlator produced sidelobes sufficiently large to be taken as false targets. The linear processor, however, was less sensitive to mismatch between the predicted and measured field. Array gain for the linear estimator was found to be 2 dB higher than for a conventional plane-wave beamformer.