Fish Finder Bathymetry

Bathymetry, the underwater equivalent of topography, is an important component of any aquatic research. Whether one is simply trying to determine the deepest spot in a waterbody or working on something much more complex, such as flow modeling, an accurate understanding of the underwater terrain is required. Traditionally creating bathymetric maps was an extremely time consuming process, requiring many hours of depth sounding and position measurement as well as a skilled cartographer. Today this is done with multibeam sonar and advanced data processing that can create high resolution maps in a fraction of the time.

The equipment necessary to accomplish this, however, is specialized and expensive. Since such studies usually only need to be done once they are generally contracted out to specialized consulting firms. Unfortunately, the high prices that such firms charge are often out of the reach of smaller research and management groups.

One solution to this problem is a hybrid approach that combines the traditional approach of many single-point depth soundings with modern technology and statistical analyses. While not as high resolution as multibeam sonar, this technique can provide accurate bathymetric maps at a fraction of the cost.

The key to these cost savings lies with the use of commercial “fish finders” that employ sonar to determine depth and structure. While most of these units are designed for real-time visual output, many are capable of linking to peripherals such as autopilots. This linkage is a data connection that continuously outputs measurements in one of a few standard formats.

I designed a peripheral that connects one such unit and uses the provided data to record depth and position at specific intervals. This allows us to automatically generate a series of georeferences depth readings by running transects across a waterbody. From this dataset we can then interpolate a continuous depth map using GIS tools.

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