How can I prove that the depth measurements from Bathyswath are accurate?

The depths measured by Bathyswath come from many different measurements and calculations. How can I be sure that they are all working correctly to give me the right answer?

There are several ways that Bathyswath users prove the accuracy of their systems. These include:

  • Comparison with previous surveys using other systems. Most sonar software can output data in ASCII XYZ (easting, northing and depth written to a text file). The Bathyswath Grid Processor can input these files and subtract them from a Bathyswath grid to give a comparison between them.
  • Surveys in areas where the depth is known. Places where the water can be taken away are good for this, such as dry docks and locks. We helped a customer in Belgium to do this recently, using a large river lock, where the depth of the concrete bottom had been accurately measured using land-survey techniques. By carefully eliminating all sources of error in their combined system, we were able to prove agreement between the sonar data and the land survey to better than 1cm!
  • Bar-checking: echosounder users use a metal bar or disk at the end of a rope hung beneath the sonar transducers. This is harder to do with multibeam systems, but it can work. However, it is usually easier to use the rope to measure the distance to the seabed itself.