Adding Tides & Starting Elevation to Sub-Bottom Data

Chesapeake Times, Vol 6 | July 2021

New for SonarWiz 7.8.0 – we are adding the ability to utilize Tide data to correct Sub-Bottom sonar data.  In addition to Tide data we are also adding a Starting Elevation value for each Sub-Bottom file. This will allow the user to specify the elevation for the survey. 

SonarWiz Sub-Bottom data has several sources of Elevation data and Depth data:

These data add together to describe where the sonar is located vertically. In other words a Vertical Offset of the Sub-Bottom sonar data. This information together with the travel time will allow a more accurate location for geological features and other items of interest. In order to better illustrate this here are 2 pictures utilizing Starting Elevation and Sensor Depth.

In the above illustration a mountain lake with a starting elevation (the highest level of the water) is shown at 1000m above sea level. The sonar is at 10m depth. The total vertical offset for the sonar is 950m elevation. Since SonarWiz uses Depth (positive down) to denote the vertical offset SonarWiz will show -950m as the start of the sonar data.

Another illustration shows a desert lake with a starting elevation of -1000m below sea level. The sonar is again at 10m depth. The total Vertical Offset for the sonar is now -1010m elevation. Since SonarWiz uses Depth (positive down) to denote the Vertical Offset, SonarWiz will show 1010m as the start of the sonar data.

So what’s the difference between Elevation and Depth values? In the above 2 examples I have stated the total Vertical Offset initially as an Elevation. Elevations are positive in the up direction (towards space). SonarWiz uses Depth which is positive in the down direction (towards the earth’s core).  Here is an illustration showing the difference:

Using Tide and Starting Elevation In SonarWiz

Tide data and starting elevation are applied to the Sub-Bottom data by using the SBP Tides and Vertical Offsets tool located on the SonarWiz Post Processing ribbon bar. 

In the SBP Tides and Vertical Offsets window simply click the Tide Height check box and choose a Tide file to apply. Then select the sonar data files to apply it to. Click the OK button to apply the new data to the selected Sub-Bottom sonar data files.

Once the data has been applied, the window will close and the Tide Height and other Vertical Offset values can be seen in the file’s properties or by using the Info At Cursor tool in the SonarWiz SBP Digitizer window.

file properties showing the vertical offsets

info at cursor tool available in SBP Digitizer window

Data can be included or excluded from the Vertical Offset calculation used to correct the sub-bottom sonar data using the application’s SBP annotation/display options.

The Vertical Offsets, including Tide Height and Starting Elevation, will be used in the various Sub-Bottom sonar related data exports. These include SEGY export, batch image export, contact export, and digitized features.

-Christopher Favreau, Chief Technology Officer