Accuracy (budget error), productivity and performances


How can I reduce the cost of the motion sensor for lake and river work

When you are surveying on the sea, with the waves moving the boat around, a good motion sensor is needed to measure the motion of the boat. If the motion measurement is not accurate, then you see "motion artefacts" in the measurements of the depths, where the depth map has waves in it that match the movement of the boat.

What is the meaning of along and across track beam width of Bathyswath?

Along and across beam width determine the size of objects that can be detected: smaller beam widths allow you to see smaller objects, and large beam widths cause objects on the bottom to be "smudged out". Bathyswath, like all swath bathymetry systems, looks sideways from the vessel, using a beam that is wide in the vertical direction and narrow at right angles to the direction that it is looking (in the direction that the vessel is going: "along track").

How do I optimise sidescan performance?

Bathyswath basically *is* a sidescan system; or, rather, it is four sidescan systems used together to measure depths as well as sidescan. One user in the USGS told us that he considers it "an excellent sidescan system that happens to give depths too".

What is PPS rising/falling, and what happens if I set it wrong?

"Falling edge" systems hold the PPS line at about 5V most of the time, and it drops to 0V when the PPS signal is active. So the sonar must synchronise when the voltage goes down, from 5V to 0V.
"Rising edge" systems hold the PPS line at 0V, and send it up to 5V when the PPS signal is sent.

What is the difference between resolution and accuracy?

Depth Accuracy tells you how sure that you can be that a depth measurement is correct. If the sonar tells you the water depth is 10 metres, is it really 10.1m or 9.9m?

Depth Resolution tells you the smallest depth difference that can be detected. So if the depth resolution is 1cm, you should be able to see a 1cm "step" in the bottom of the sea.

These two figures are very different. A sonar might be able to resolve a small object (resolution), but it might not be able to tell exactly how deep it is (accuracy).