Sub bottom profiling - lakes / rivers

[kbrewman]

Hi All,

We have a Knudsen Pinger SBP unit. We have gotten some great data from it. One problem that comes up is the affect of waves. We use a open 16Al boat, so that limits us to "fair weather surveys". Any thoughts on how to deal with waves in the data? I have looked into heave sensors which get really expensive, and are intended more for big boats in marine settings, some of them are more $$ than the SBP! FYI we typically turn back if the waves are anything more than 1-2 feet. I don't do the processing side, but seems like you should be able to filter the data for this, it is easy to spot effects of waves in the data.

thanks

[GuyM]

Done some stuff on lakes where we digitised the seafloor, then smoothed it (low pass spatial filter)

You can then calculate a static shift from the smoothed and original profiles to apply to the data; one way is to:

- extend the data by 500ms
- shift the data down by 500ms
- shift the data up by the digitised seafloor (so seabed now flat at 500ms)
- shift the data down by the smoothed seabed
- shift the data up by 500ms

The 500ms shift is there to preserve the water column and start of the sea-floor arrival; use a smaller buffer if you need to.
You could just calculate the delta shift, but this is easy too.

Works pretty well; you just have to careful with the low pass spatial filter to make sure you do not remove any structure.