That part is clear, but I’m wondering why that is something you’re thinking and concerned about.
I don’t have extensive experience with multibeam sonar, so it’s possible there are unique considerations involved that I’m not recognising, but the analogy I’m considering is:
If you take a photo in a very long room, the ceiling does not prevent the light from other parts of the room reaching your camera, right? Accordingly,
- a camera can see just as far forwards with or without a ceiling above it, but
- the ceiling does prevent seeing up by as much (i.e. the vertical field of view is effectively reduced), and
- lights in the ceiling may be bright enough that they add some noise to other parts of the image by reflections in the optics (which is like the sound pulses reflecting partially back towards the transducer from waves in the water surface).