Abstract

Calibration can greatly increase the utility of collecting seafloor backscattering strength with multibeam echo sounders (MBES). A calibration procedure to determine high resolution, three dimensional transmit and receive beam patterns of a Reson SeaBat 7125 MBES was performed using the fresh water calibration tank at the University of New Hampshire. The measurements employed an omni-directional Reson TC4034 projector/hydrophone as a reference transducer at an acoustic distance of 13 m. The multibeam sonar system was configured for 256 beams equi-angle mode and operating frequency of 396 kHz. The transmit beam pattern was computed for across-track angular range between +/–90o in 0.1o increments and along-track angular range between +/–2.55o in 0.09o increments. Receive directional characteristics were measured for the across-track range of +/–120o in 0.1o increments with along-track angular range of +/–1.23o in 0.18o increments. With these measurements, a three-dimensional plot of the transmit beam pattern was computed for the entire range of angles, although for the receive beam pattern it was only determined for the 0o along-track angle. The reduced angular coverage of the receive beam pattern was due to discrepancies in the off-axis results that are thought to be related to receiver saturation. Measurements for the transmit beam pattern show a –3 dB beamwidth of 0.99o for across-track angle of 0o with side lobes below –17 dB. The results show an unexplained curvature in the transmit beam pattern that would have gone un-noticed during a two dimensional beam pattern measurement. An interference effect causing ripples and attenuation of the transmit beam pattern was also observed. This effect is thought to be caused by a second 200 kHz projector mounted parallel to the 396 kHz projector. This interference occurs at an across-track angular region between +30o and +75o with gradual decrease in amplitude of about 3 dB. The receive beam pattern measurements show a –3 dB beamwidth of approximately 0.62o for the most inner beams (beams 128 and 129) and of approximately 1.40o for the most outer beams (beams 1 and 256) at along-track angular position of 0o with side-lobes below –26 dB for the most inner beams and below –17 dB for the most outer beams.

Publication Date

9-2010

Journal or Conference Title

IEEE Oceans

Conference Date

Sep 20 - Sep 23, 2010

Publisher Place

Seattle, WA, USA

Publisher

IEEE

Digital Object Identifier (DOI)

10.1109/OCEANS.2010.5664519

Document Type

Conference Proceeding

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