BlueView Sonar Selection

Discussion space for posts that don't fit into the other categories, such as issues with VideoRay products, or general ROV tips.

BlueView Sonar Selection

Postby tom_glebas » Wed Jun 23, 2010 7:30 pm

I've put together some thoughts on sonar selection, specific to BlueView models. These are generalities, as certain special cases may change the analysis or conclusions.

If you haven't already, you can also see:

Sonar Factors:

Gain - signal strength which limits maximum range for a given frequency (basically constant for all models)
Range - how far the sonar can "see"
Resolution - how detailed the image is
Field of View - the horizontal angle of the beam
Vertical Beam Spread - the vertical angle of the beam
Update or Ping Rate - how fast the image updates (affects ability to navigate in real time)
Hydrodynamics - how much drag
Weight in Air - how heavy it is to transport on land
Weight in Water - how much buoyancy is required (may limit other accessories at the same time)
Depth Rating - how deep can you use the sonar

With respect to BlueView the following issues are the main ones that should be considered (in each case, all other factors being equal):

Lower frequency has longer range
Higher frequency has better resolution
Wider field of view covers more area at an equal distance
Narrow field of view has faster update rate
Smaller size head has less drag
Larger vertical beam spread may be easier to obtain better overall images
Smaller vertical beam spread may provide more detail if there are objects at different heights and the same range, but it is less tolerant of the mounting angle and a good overall image may be more difficult to obtain

Additionally some operational considerations:

Shorter ranges have a faster update rate, which can be used to compensate to some extent when using a wider field of view
Smaller on-screen image size may update faster too since there are fewer pixels to "paint".
Faster computer processor may update faster since it can "paint" faster
Shorter Tether may update faster due to lower noise and less packet loss

In order to answer which of these is the most important to you, your objectives and operating conditions must be considered:

More current - less drag would be better (450 or 900-45 would be better choices)
Need more detailed images or looking for small objects - higher frequency would be better (900 over 450 or for special purpose, 900-2250DF)
Larger search areas - longer range might be better since you can turn and sweep an area faster than you can navigate from place to place with a wider field of view and less range (450)
Large target size - wider field of view may allow a single image to capture the whole scene (shipwreck) rather than having to manually mosaic single narrower scans (900-130)
Ability to maintain a heading will navigating toward a target - a faster ping rate will be better if there is any problem holding a heading (i.e. cross currents, surge, etc.), and less drag may also be easier to pilot (450 or 900-45)
Need to see close? 900 has 2 m, 450 has 5m optimal minimum range, but both will see closer

I'm sure there may be other considerations, and I hope this hasn't muddied the water (bad pun).

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