Expanded CSF Sample Count Options

Chesapeake Times, Vol 6 | July 2021

Recently we’ve seen a good amount of interest in higher-resolution sidescan. Recordings can be made at 10,000 or more samples per channel, to allow for centimeter-level resolutions over relatively wide swaths. Customers want to make the most of the systems they’ve invested in and offer high-resolution deliverables.

To accommodate these needs, the upcoming 7.8.0 release of SonarWiz will include some new sidescan import sample count options. Previously, sidescan files could be imported with 1024, 2048, or 4096 samples per channel. Now, a user-selectable or automatically-detected number of samples can be imported, with a significantly expanded overall range.

Here’s a look at the advanced sidescan import options window (“Advanced Settings…” button from either the sidescan import Open window or Options/File Options/SSS Import Settings:

The “Manual” setting allows for a sample count per channel to be entered by hand. The allowable upper limit has been increased to 32,768 samples per channel (the lower limit has been lowered as well, due to some less-frequent use cases revolving around processing speed, disk space, or older recordings). For the frequent case in which a set of files with fixed, known sample count needs to be imported, but that sample count isn’t one of the previously-offered powers of two, this is a good option. Raw samples are brought in as-is, with no resampling and no wasted disk space.

Properties of some sample Klein data with exactly 2,400 samples per channel in the original recording:

The “Actual” setting allows for automatically increasing the sample count a file can hold as it’s imported. The allowable sample count for a file starts off low in this mode, at the minimum, and is increased to hold additional samples each time a larger sample count is detected in the raw sonar file. Importing multiple files at once with this mode might result in differing sample counts among the resulting CSF files; each import is treated individually. For situations in which you want to bring in files at full resolution without having to figure out the sample count ahead of time, this is a good choice.

An additional benefit of the “Actual” mode is that, like the manual mode above with a known fixed sample count, the data isn’t resampled to fit into a fixed-sized array. Before, it could happen that a sample count change in the middle of an import file would result in subsequent pings being of higher average intensity than prior ones due to the resampling method used. This mode could be sub-optimal in terms of disk space; though rare, some variable-length recordings could switch from a low sample count to a much higher one just near the end of the file, resulting in much of the space occupied by the earlier records being wasted.

We’re excited about the new sample count offerings for CSF sidescan files. There are a good number of additional improvements that could fall naturally out of these changes, so expect future versions of SonarWiz to expand on these capabilities.

– Jonathan Fleetwood, Engineer