Sidescan Sonars Developments

Sidescan Sonar Technology has gone through an evolution the last years. Sidescan sonar is mainly used for the detection of objects and bottom structures.  it gives very highly detailed images indicating not only the existence of objects but also the type of material (strong reflector or weak reflector). In this article you can find a review of the latest technical developments.


Sidescan Sonar Definition


Side scan sonar creates a picture or an image of the sea floor. It measures the strength of how "loud" the return echo is, and paints a picture.

Hard areas of the sea floor like rocks reflect more sound and have a stonger or louder return signal than softer areas like sand. Areas with loud echoes are darker than areas with quiet echoes. Objects or features that rise above the sea floor also cast shadows in the sonar image where no sound hit. The size of the shadow can be used to guess the size of the feature.



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Sidescan Sonars vs Multibeam Echosounders


SSS systems do not provide direct height/depth information; this has to be inferred from the image (object height as a ratio between fish altitude, shadow length and total distance between fish and end of shadow). There are manufacturers providing so-called hybrid SSS / bathymetric systems. In general, these systems provide full SSS images with interferometric multibeam bathymetry.
Conversely, a beam forming multibeam echo sounder (MBES) will provide depths from dedicated transducer arrays allowing for high-accuracy beam discrimination. Nowadays, most MBES systems can also provide backscatter information.


The difference between MBES backscatter and a true SSS is that the MBES will provide one backscatter value per beam whereas the SSS will provide an (almost) continuous signal thus giving a higher resolution. 


Sidescan Sonar Parameters


A SSS system is defined by a number of parameters of which the range and resolution are probably the most important. The resolution of the SSS defines the image quality and can be divided in ‘along-track’, ‘across-track’ and backscatter resolution.


1. Range


The range defines how effective the SSS will be (how much of the bottom can be surveyed in one track). Range is effectively a function of the frequency at which the SSS operates; the higher the frequency the smaller the range (500m @ 150kHz vs 35m @ 1600MHz).

Sidescan sonar Pulsar



2. Range Resolution


The across-track or range resolution defines what the smallest distance is between two objects that are ‘behind’ each other in the direct path of the SSS beam. 



 Sidescan Sonar Chrip


3. Along-track Resolution


The along-track resolution of a SSS is traditionally defined as the product of the so-called horizontal beam angle of the side-scan (typically between 0.2° and 1.5°), the effective range and the tow-speed of the SSS. A small beam angle at short range will allow the detection of small objects spaced apart along the track of the SSS.



Sidescan sonar D3500













4. Multibeam and Multi-ping


Currently there are two different solutions employed by SSS manufacturers to achieve a higher tow rate. One is to make use of multiple beams. If, for example, 5 beams are used on a single side of the SSS then the effective along-track resolution is multiplied by 5 allowing higher tow speeds. The alternative solution is to have multiple pings in the water. With CW type SSS this is not possible but with the CHIRP type this can be done. 



 Sidescan sonar System 3900


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