Creating single target detection variables from dual-beam data

Before you begin

The reliability of detected single targets depends on the correct configuration of calibration and transducer geometry settings for the first (and second) operand. In many cases the input operands are raw variables. When the operands are virtual variables, the rules under the inheritance of properties provide a path to the original raw variable at the start of a chain of virtual variables.

• Environment and echosounder system calibration settings are displayed on the Calibration page and may be modified with an Echoview calibration supplement file (ECS file).
• Note: TVG and TVG range correction can affect the suitability of an Echoview single target detection method for your data.
  For more information refer to:
  • About time varied gain
  • TVG range correction overview
  • Are my single target detection results affected?
• The transducer object is specified through Transducer under the Geometry section of the Calibration page. Transducer settings (to specify a vertical beam or a horizontal beam) may be modified through the Transducer Properties for the Transducer object on the Dataflow window.
• This operator accepts two TS variables as operands (a narrow beam and the related wide beam TS variable). Each operand must be associated with a different transducer and the 3dB beam angle settings must be defined for each transducer.
  • You associate a transducer with a variable on the Calibration page of the Variables Properties dialog box.
  • Values for the major and minor axis beam angles are displayed by the Details dialog box (F9). Use an ECS file to modify the SourceCal 3dbBeamAngles for the wide beam and narrow beam.

e.g. Snippet from an ECS file for Biosonics dual beam data.

SourceCal (wide beam) (channel 1)

MajorAxis3dbBeamAngle = 20

MinorAxis3dbBeamAngle = 20

SourceCal (narrow beam) (channel 1)

MajorAxis3dbBeamAngle = 6.80

MinorAxis3dbBeamAngle = 6.80

Procedure

To create a single target detection virtual variable from dual-beam data:

1. Open the Dataflow window.

2. On the Shortcut (right-click) menu, click New to display the New variable dialog box.

3. On the New Variables dialog box:

   1. In the Name box, enter a name for the single target virtual variable.
   2. In the Operator list, select a dual-beam single target detection operator.

4. Click OK to display the Variable Properties dialog box.

5. On the Operands page:

   1. In the Operand 1 list, select a narrow beam TS variable.
   2. In the Operand 2 list, select the related wide beam TS variable.

6. Click the Single Target Detection tab.

7. On the Single Target Detection page:

   1. In the Single target detection parameters section, enter required single target detection settings. See Single target detection page for settings information. See Single target Method 1 or Method 2 for algorithm information.
   2. In the Exclusion section, select exclusion lines (if required).

Note: This page contains default settings to begin with. If the resulting echogram does not contain as many single targets as you expect, relax some of the constraints on this page. See Tuning single target detection algorithms for more information.

8. Click the Data tab.

9. On the Data page:

   1. In the Minimum threshold section and Maximum threshold section, select the desired options (if any) and enter threshold settings.
   2. In the Filter single targets section, select the desired options (if any) and enter filter settings.

10. Click OK.

To display the single target virtual variable you created; on the Dataflow window, double-click the new virtual variable.

See also

About single target detection
Beam compensation BioSonics dual beam
Simrad and Echoview terminology