SUPPORT > SIDE SCAN IMAGERY > TIPS FOR GOOD IMAGERY

Listed below are some useful tips to help you produce good images from your StarFish sonar.

Towing Speed

When towing the StarFish, remember that it is 'pinging' at a fixed rate (depending on range). The faster you tow the fish, the more compressed images will appear on the display, and its towing depth may become shallower as the drag on the sonar transducer head and towing cable increases. For long ranges, try to tow at speeds between 1 and 3 knots, while shorter ranges can be used with speeds of 3 to 6 knots.

Towing Depth

The towing depth of the sonar is an important factor to consider when interpreting heights of submerged objects from their acoustic shadows. Towing too close to the seabed will make shadows appear very elongated (like shadows cast from objects at sunset), while towing too high from the seabed will give a 'birds-eye' type view, but with minimal shadows.

Towing Position

Tow the sonar at a depth below the boat keel, so there is minimal risk of it receiving echoes back from the hull. These will appear as mirror or 'ghost' images on the sonar display. If any attachments are added to the StarFish, ensure that a symmetry is maintained (when looking from the front), to prevent the StarFish from towing at a rotated angle.

Boat Navigation

When surveying an area, think about the course you will steer your vessel over. Try to divide the area into a grid of long straight runs, with 180° turns at the end.

Remember that as the boat turns, the acoustic beams from the inside of the turn will overlap, while the outside ones will be covering more seabed - consequently the imagery produced will appear distorted and hard to interpret in these areas.

Give plenty of clearance between your boat and other vessels or surface / mid-water hazards, and try and avoid the aerated water left in the wake of other boats, as this will be acoustically visible for some time should you cross through it with your sonar.

Waves, Wake and Surface Chop

As your StarFish is operating several metres below the surface, it should be largely unaffected by waves and surface chop on the water. However, it still is susceptible to movements on the towing cable, so in rough conditions it is advisable to deploy longer lengths of cable, reducing the angle of the cable to the sonar transducer head.

Your StarFish will not perform well in rough stormy conditions.

Please remember, that when in a boat, your own safety is paramount, and should not be compromised while trying to achieve good sonar imagery.