Knowledgebase
Adjusting the image in Sidescan Survey
Posted by Jerry Knisley, Last modified by
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on 21 December 2016 02:09 PM

            SIDESCAN SURVEY PROGRAM

The sidescan survey program is used to view real time sidescan data as it is collected. The program records the raw amplitude data sent by the sensor. The real time image can be adjusted to aid the surveyor in identifying targets as they appear.

To adjust the image there are several factors that can be used.  A good image is critical to interpreting the sidescan target.

  • Signal Gain
  • Color
  • Brightness and Contrast
  • Signal Range

When adjusting the image it is best to adjust one item at a time as the various options all relate to the overall image and many users have spent time fighting the affect of one setting with another.

SIGNAL RANGE

The first item to get correct is the Signal Range. The Signal Range is set using the Sidescan Signal window. In the image below there are two bars that allow the user to adjust the allowable signal in the display. These bars are shown with the current signal so that the operator can make real time adjustments.

Bringing the upper bar closer to the lower bar will decrease the color resolution. In the images below the bar is adjusted for the starboard channel. 

Above the bar is set to show an even bottom. Below the bar is lowered and the change is easily visible, if you missed it, the red arrow indicates when the change occurred. Each channel can be set individually.

COLOR

The color of the image is set in the Sidescan Controls dialog. There are several pre-configured color palettes available. Every user will generally have their own favorite.  If the user chooses the CUSTOM option the Custom Hue slider is enabled allowing the user the freedom to choose a color pallete best suited for their purpose. As you can see in the pastel image below where the custom hue slider was adjusted from one end to the other.

Contrast and Brightness

The Brightness slider is used to adjust the image by simplying adjusting the picture of the image. The reason for explaining this is that the gain will have an affect on the adjacent returns that the Brightness option does not. Each can have similar appearance changes but in different ways. In the imgae below the slider started at 0 in the middle and was moved to each end.

The contrast slider works with the brightness slider to adjust the image. The closest control to the contrast slider is the Signal Range bars discussed above. As can be seen in the image below the contrast slider is similar to adding a screen over the entire image. While the image has changed similar to the image above, the effect is slightly different. The contrast and brightness adjustements are used together to make a better image.

GAIN CONTROL

The Gain Control in the program comes in many varieties. In the SIDESCAN SIGNAL window there is an option to see the RAW signal or the PROCESSED signal. The PROCESSED signal will show the signal after any gain has been applied. This allows the user the ability to see what they are doing to the signal for display purposes.

  • Basic Gain is used as a linear gain starting at the ping and applied outward.
  • Auto TVG attempts to approximate the amount of gain to apply based upon the signal using binned data.
  • Apply TVG = db's / 100 meters is used to adjust the gain using a linear equation similar to basic gains.
  • Apply TVG = P1*log(r) + P2*(r) + P3 is a formula that attempts to provide the best gain based upon the distance from the sonar. This formula works to overcome signal degradation caused by range.

Each of these controls can be used independently or in conjunction with one another. As they tend to have the same effect it is not normal to use them together. Each of these gains may work well with one system and not well with another. It is recommended that the user works out the best gain for their system as well as the current environment.  

 

In the last image is the SIDESCAN SIGNAL window showing the effect of the AUTO TVG option on Klein sonar data.