Comparison of acoustic and non-acoustic methods of vertical line array element localization

SWellEx-3 (Shallow Water evaluation cell Experiment 3) was conducted in July 1994 west of Point Loma in 200 m water. During the experiment, a MPL 64-element, 120-m aperture, vertical array was deployed on the ocean bottom from the R/P FLIP. Located 2-m above the shallowest array element was a self-recording package equipped with depth, tilt, and direction-of-tilt sensors, thereby permitting array element localization (AEL) to be performed nonacoustically. In addition, AEL was performed acoustically using two different approaches. The first approach made use of transponder pings (in the vicinity of 12 kHz) received by high frequency hydrophones spaced every 7.5 m along the vertical array. The second approach was based on a self-cohering technique where matched-field processing was performed on a low frequency, multi-tone (50-200 Hz) sound source being towed at various ranges and azimuths from the array. The focus of this paper is on a comparison of the time-evolving array shape estimates generated by these three different methods. As shown, all three provide a consistent picture of array motion throughout the 6 hour period analyzed