Side scan sonar uses a pulsed beam of sound transmitted horizontally on both sides of a ship to image the seafloor. Reflections are recorded to provide high resolution images of small seafloor objects. It consists of an underwater sensor towed behind the ship connected by cable. For optimal detection, the tow fish height should be maintained between 10-20% of the range scale used, adjusting the range scale or transducer angle if needed. Sonar lines should be run within 20 degrees of tidal streams and along depth contours to maintain tow fish height, or perpendicular to sandwave crests in those areas. Target heights can be estimated using similar triangles and measurements of shadow length and slope range on the sonar image.

1. SIDE SCAN SONAR

2. Concept of Side Scan Sonar
• A pulsed beam of sound, narrow in the
horizontal plane and broad in the vertical
plane.
• It transmit either side of the ship track.
• The transmissions reflected back from the
seafloor to transducers.
• The beam geometry and short pulse length
provide good resolution of small object on
seafloor

3. Side Scan Sonar
• Recording device
• Underwater sensor (Tow fish)
• Cable to connect

4. Fish Height
• Should maintain at 10-20% of the range scale in
use.
• This height provide optimum geometry for target
detection and classification.
• If the water is too shallow, reduce the range
scale.
• If the water is too deep, change the transducer
depression angle from 10% to 20%.
• A rough guide, an initial length of 30m should be
paid out from a water depth of 20m and speed of
6 knots.

5. Line Direction
• Lines should be run within 20 degrees of the
direction of tide stream. This reduces uncertainty
with respect to fish position.
• In condition of strong wind and/or tide it maybe
necessary to run lines into the wind/tide to retain
ship control at the low speed over the ground.
• Line should be run along the contours to maintain
fish height with ease.
• In area of large sandwave, lines should be run
perpendicular to the direction of the wave crests.

7. Determine Target HeightDetermine Target Height

8. • By similar triangle,
H = S x h
R + S
• The length of shadow (S) should be measured
at the deepest part.
• The slope range (R) should be measured to
the corresponding point.

9. THANK YOU