Sample statistic subtract

This operator is useful for background noise subtraction for multibeam echograms. For more information on options for noise removal, refer to Background noise in Echoview.

The Sample statistic subtract operator removes noise from the first operand by averaging the pings in the second operand, and subtracting the results from each ping in the first operand. The resulting virtual variable has the same ping geometry as the first ping in the first operand.

The algorithm requires:

• two input operands specified on the Operands page of the Variable Properties dialog box.
• a Subtraction domain specified on the Sample statistic subtract page of the Variable Properties dialog box.
• a Sample exclusion value, expressed as a percentage of range from the mean sample, specified on the Sample statistic subtract page of the Variable Properties dialog box. Any sample values outside the interval are excluded (for calculation). Refer to Step 1.b. of the algorithm.

Note: If the echogram representing the background noise contains fish (targets), subsequent multibeam target detection on an echogram derived from the Sample statistic subtract variable will be adversely affected (you will get poorer target detection).

The algorithm works as follows.

In each beam of each ping:

1. Calculate the Mean, Minimum and Maximum sample values
   1. If Sample exclusion is 0% or 100%, return the Mean sample value (data are unchanged).
   2. If Sample exclusion has a value other than 0% or 100%.
      1. Calculate the Adjusted minimum sample value, Adjusted maximum sample value and Adjusted mean sample value as follows:
         
         Adjusted minimum sample value = Mean sample value - Sample exclusion (Mean sample value - Minimum sample value)
         
         Adjusted maximum sample value = Mean sample value + Sample exclusion (Maximum sample value - Mean sample value)
         
         

         Where:

         

         
         
      2. Exclude any samples above the Adjusted maximum sample value or below the Adjusted minimum sample value.
      3. If samples occur within the Adjusted interval, return the Adjusted mean sample value.
      4. If no samples occur within the Adjusted interval, return the Mean sample value.

See also

Sample statistic subtract operator
Background noise in Echoview
Variable properties dialog box

Echoview Help file 5.2.21 for Echoview 5.2.55 Monday 21st May 2012

Please report any errors or omissions to support@echoview.com.