Detecting schools on multibeam data

Before you begin

See About 3D school detection for an overview before detecting schools.

Consider using one of the many multibeam operators available for preparing data. This may help to significantly improve the schools you detect. For example, you might wish to create a virtual echogram using the beam closing filter if the data representing the school(s) contains a lot of holes. See Multibeam convolution operators for some of the effects you might achieve.

Note: If you are using data from a scanning sonar using instrument scanning then you should prepare your instrument scanning data for school detection before continuing.

Detecting schools

To detect schools on multibeam data:

1. Display the multibeam echogram from which you wish to detect schools.
2. Apply a Minimum data threshold (and optionally a Maximum data threshold) on the Data page of the Variable Properties dialog box until the data that you believe represent the school(s) are clearly visible and distinct from the background noise on the multibeam echogram.
3. The Analysis page of the Variable Properties dialog box allows you to specify Exclude above and Exclude below surfaces, surface offset and minimum range exclusion. Such surfaces enable the detection to avoid data like ring down noise or data beyond a specified range.
4. On the Echogram menu, click Detect schools.
5. On the Detect 3D Schools dialog box, complete the settings on each page (the settings you enter can have performance implications).
   1. If you have selected the Cruise scanning algorithm make sure your data meets any restrictions imposed by that algorithm.
   2. If you have selected the Instrument scanning algorithm make sure your data meets any restrictions imposed by that algorithm.
   3. If you have selected the Target-locked scanning algorithm make sure your data meets any restrictions imposed by that algorithm.
   4. If you have selected the By ping algorithm make sure your data meets any restrictions imposed by that algorithm.
6. Click Detect.
   Note: The detection process can take quite a long time. When it is complete, a message is displayed to notify you of how many schools were detected.
7. One or more new 3D regions (possibly with vacuoles) are created (one for each detected school).

Notes:

• To view a 3D region you must add it to a scene. See the Objects page of the Scene Properties dialog box for more information.
• Each 3D region has its own (3D Object) Properties and is listed on the Regions window.
• 3D regions may be integrated.
• You can view details about vacuoles in a 3D region and delete vacuoles from a 3D region on the Vacuoles page of the (3D Object) Properties dialog box.
• You may wish to experiment with different thresholds, operators and school detection settings then compare the results in 3D space. Echoview allows you to assign colors and transparency levels to schools so you can compare multiple schools in the one 3D scene, see About 3D school detection for an example. You apply color and transparency settings on the Display page of the (3D Object) Properties dialog box.
• Size, shape and position in a scene are calculated using geographic coordinates that have been corrected for transducer geometry.
• To run a detection on a displayed ping.
  • On the multibeam echogram, display a ping of interest.
  • On the Shortcut menu (right-click), select Detect Schools In This Ping.
• This detection automatically uses the settings on the 3D Schools detection Properties dialog box and the By Ping algorithm. Make sure your data meets any restrictions imposed by that algorithm.

See also:

About 3D school detection
Creating 3D regions
3D School detection algorithms
Preparing instrument scanning data for 3D school detection
About surfaces