Side-scan sonar

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Diagram of sidescan sonar

Side-scan sonar (also sometimes called side scan sonar, sidescan sonar, side imaging sonar, side-imaging sonar and bottom classification sonar) is a category of

create an image
of large areas of the sea floor.

Uses

Side scan sonar is used when you want to image large areas of the seafloor quickly. Applications include

marine archaeology, shipwreck hunting, search and recovery (SAR), and environmental monitoring. [1] In conjunction with seafloor samples, it is able to provide an understanding of the differences in material and texture type of the seabed. Side-scan sonar imagery is also a commonly used tool to detect debris items and other obstructions on the seafloor that may be hazardous to shipping or to seafloor installations by the oil and gas industry. In addition, the status of pipelines and cables on the seafloor can be investigated using side-scan sonar. Side-scan data are frequently acquired along with bathymetric soundings and sub-bottom profiler
data, thus providing a glimpse of the shallow structure of the seabed. Side-scan sonar is also used for fisheries research, dredging operations and environmental studies. It also has military applications including mine detection.

How it works

Side-scan uses a sonar device that emits conical or fan-shaped pulses down toward the seafloor across a wide angle perpendicular to the path of the sensor through the water, which may be towed from a surface vessel or

kHz; higher frequencies yield better resolution
but less range.

History

Side-scan sonar image of shipwreck "Aid" in Estonia
Side-scan sonar image of submerged bridge at the bottom of Lake Murray in South Carolina

Technology

The earliest side-scan sonars used a single conical-beam transducer. Next, units were made with two transducers to cover both sides. The transducers were either contained in one hull-mounted package or with two packages on either side of the vessel. Next the transducers evolved to fan-shaped beams to produce a better "sonogram" or sonar image. In order to get closer to the bottom in deep water the side-scan transducers were placed in a "tow fish" and pulled by a tow cable.

Up until the mid-1980s, commercial side scan images were produced on paper records. The early paper records were produced with a sweeping plotter that burned the image into a scrolling paper record. Later plotters allowed for the simultaneous plotting of position and ship motion information onto the paper record. In the late 1980s, commercial systems using the newer, cheaper computer systems developed digital scan-converters that could mimic more cheaply the analog scan converters used by the military systems to produce TV and computer displayed images of the scan, and store them on video tape. Currently data is stored on computer

hard drives or solid-state media - the data is typically displayed in grayscale or color images, known as side scan sonograms, which provide a visual representation of the underwater environment. [3]

Military application

One of the inventors of side-scan sonar was German scientist, Dr.

Harold Edgerton
at MIT.

Military side-scan sonars were made in the 1950s by Westinghouse. Advanced systems were later developed and built for special military purposes, such as to find H-Bombs lost at sea or to find a lost Russian submarine, at the Westinghouse facility in Annapolis up through the 1990s. This group also produced the first and only working Angle Look Sonar that could trace objects while looking under the vehicle.

Commercial application

side-scan image of the freighter Choctaw

The first commercial side-scan system was the

wreck of the RMS Titanic
.

For surveying large areas, the GLORIA sidescan sonar was developed by Marconi Underwater Systems and the

Asdic.[5] It was used by the US Geological Survey
and the IOS in the UK to obtain images of continental shelves worldwide. It operated at relatively low frequencies to obtain long range. Like most side-scan sonars, the GLORIA instrument is towed behind a ship. GLORIA has a ping rate of two per minute, and detects returns from a range of up to 22 km either side of the sonar fish.

See also

  • Aperture synthesis – Mixing signals from many telescopes to produce images with high angular resolution
  • Beamforming – Signal processing technique used in sensor arrays for directional signal transmission or reception
  • Phased array – Array of antennas creating a steerable beam
  • Sonar 2087 – Towed array sonar
  • Synthetic aperture sonar
     – Form of sonar using post-processing of sonar data

References

  1. ^ "A Smooth Operator's Guide to Underwater Sonars and Acoustic Devices". Blue Robotics. Retrieved 2024-01-12.
  2. ^ "A Smooth Operator's Guide to Underwater Sonars and Acoustic Devices". Blue Robotics. Retrieved 2024-01-18.
  3. ^ "A Smooth Operator's Guide to Underwater Sonars and Acoustic Devices". Blue Robotics. Retrieved 2024-01-12.
  4. United States Patent Office
    .
  5. ^ Rusby et al. 1973

External links

Wikimedia Commons has media related to Side-scan sonar.
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