Import an XTF file that contains Side Scan data into Perspective, wait for the Navigation track to be drawn and dismiss the Mosaic Wizard. Double click the line in the Map view to open the Side Scan waterfall window:
It is important that an area of smooth seabed is chosen, strong reflectors will cause distortion of the curve resulting in along-track stripes of high and low gain artifacts in the mosaic. If the data have not been bottom tracked you should do that first.
Turn on slant range correction:
In the example note the stronger returns directly below the towfish and towards the edges of the swath.
Click the Auto TVG button:
There are a number of different option available in this dialog box, however the default settings have been used successfully with many different types of sonar data, specifically the Mean option works best (feel free to experiment with the other options)
The Brightness and Contrast sliders are self explanatory, Window Size adjusts how quickly the gain is allowed to change in the across track direction (effectively the steepness of the resulting TVG curve) small values allow for more rapid changes, in this example the Brightness was adjusted to 40 and the Window size to 7:
To see the effect of the changes click Apply Current Settings note that the image may have across track stripes of higher and lower gain at this point - this is normal and is caused by each individual ping of data having a slightly different TVG gain curve applied, when the TVG Curve is computed the gain is averaged.
When the image has been adjusted to your satisfaction click Generate Curves:
TVG curves for each Side Scan Sonar channel are generated and the correction applied to the waterfall display, note that the gain stripes have disappeared. The display now shows how the data will appear in the mosaic, cycle through the channels to see the different TVG curves for each channel. You may also force one channel to be the setting for all channels, this is useful when its only possible to find a usably smooth seabed return on one of the channels.
Save the settings to a TVG_xml file:
During the creation of the mosaic use the Edit TVG Curve button to select the correct tvg_xml file:
