Sidescan Sonar Beam Function and Seabed Backscatter Functions From Trace Amplitude and Vehicle Roll Data

Abstract

A sidescan sonar's beam function (BF) (the sonar's transmit-receive response versus inclination angle in the sonar's frame of reference) can be extracted from an ensemble of contiguous sonar traces affected by sonar vehicle roll for a uniform seabed. The rotation of the sonar's frame of reference relative to the seabed's frame of reference is employed to extract a number of discrete overlapping beam subfunctions each with angular extent corresponding to the extent of vehicle roll. These are then reconciled to form a composite sonar BF. A seabed backscatter function (SF) (the backscatter response of the seabed versus inclination angle in the seabed's frame of reference) may subsequently be inferred with respect to the BF from trace data, whether affected by roll or not. Independent sonar BF and seabed SFs allow the effect of sonar vehicle roll to be corrected when BF compensation is applied to images, and the effect of seabed slope to be corrected when SF compensation is applied. In an alternate approach to extracting a sonar BF, a seabed SF may be extracted first from the sonar traces affected by vehicle roll, by extracting a number of overlapping backscatter subfunctions, and reconciling these into a composite SF. The sonar BF may then be inferred from the trace data with respect to the SF. Seabed SFs inferred from trace data with respect to the BF may be used as a basis for seabed characterization.Index Terms-Backscatter, beam function, sidescan sonar. 0364-9059

On the Sediment Dynamics in a Tidally Energetic Channel: The Inner Sound, Northern Scotland

“…Satisfactory estimates of the sonar beam function are the key to successfully applying the angular based corrections. A method to extract sonar beam functions from data affected by sonar vehicle roll is described by Tamsett and Hogarth [23] and this has provided good estimates of sonar beam functions. Correcting for the non-seabed effects on sonar amplitude outlined above, and normalising the seabed response for all angles to that at a reference inclination angle (30˝), means that acoustic colour becomes a meaningful property of the seabed.…”

Colour Sonar: Multi-Frequency Sidescan Sonar Images of the Seabed in the Inner Sound of the Pentland Firth, Scotland

“…Beam functions and seabed backscatter functions are dependent on sonar carrier wave frequency. Beam functions were estimated by extraction from sonar trace and sonar vehicle roll data using the method of Tamsett and Hogarth [6] (patent pending WO2014/170213) from just over 600 contiguous traces affected by˘5˝of roll from a swath running over a rocky seabed approximately parallel to the dip direction exhibiting an approximately uniform seabed across swath. The method takes advantage of the rotation of the sonar's frame of reference with respect to the seabed's frame of reference during sonar vehicle roll.…”

“…To display a sonogram montage as a chart, the backscatter values along traces (across sonograms) are normalised to the seabed response at the reference inclination angle θ re f , say 30˝ [6]. At angles much less than normal incidence, the natural backscatter amplitudes are small and visually not very distinguishable from shadow.…”

“…The effects of sonar beam function and seabed backscatter function are angular rather than time-varied effects and more difficult to account for. It is only relatively recently that adequate corrections have been devised (Hughes Clarke, Danforth and Valentine [5]; Tamsett and Hogarth [6]). Further details of these corrections are provided in the section covering the processing of the experimental data presented in this article.…”

Obtaining High-Resolution Seabed Topography and Surface Details by Co-Registration of Side-Scan Sonar and Multibeam Echo Sounder Images

“…As for the SSS, there are two types of operations: towing operation and hull-mounted [5]. The first type is more popular given that the second type of operation may degrade the SSS backscatter image quality because of the platform movements caused in the surveying process [5,7]. When towing, the SSS is usually installed in a towfish and towed by a cable behind a surveying vessel (Figure 1a).…”