Detecting schools on single beam data

Schools are detected from the data displayed in an echogram by thresholding the data and using an edge detection algorithm.

Before you begin

See About 2D school detection for an overview before detecting schools.

See Using the School detection module and School detection module for detailed information before detecting schools.

It may be useful to assess your data with respect to fish density. The index for the number of fish per acoustic sampling volume may help you separate data for fish in schools from data for single fish.

It may be useful to use noise removal operators to identify and remove noise from your data.

It may be useful to use lines to exclude data when detecting schools, this can decrease the detection time.

School detection is unsuitable for echogram data that have both heave and CTD applied; the detection can fail because pings have different start and stop ranges. To workaround this issue, use a Resample (by pings) operator, to apply the ping geometry of the first ping of operand 1 with CTD applied. On the echogram with a SoundSpeedProfile and CtdDepthProfile applied, the ping geometry of ping 0 (under the mouse pointer) is displayed under the Range section of the Details dialog box. For ping 0, note the number of Data points, Start range and Stop range. Suggested resample settings are:

All pings in interval
Number of pings in interval = 1
Resample operator = Mean
Custom range values as noted (Data points, Start range, Stop range).

Specify the Platform type under the Position page of the Platform Properties dialog box. A fixed platform and the echogram Grid supports a water current speed data and water current distance calculations.

Specify the Distance mode, associated with the Platform type, under the Schools page of the EV File Properties dialog box. A detection under a fixed platform requires a Distance mode of Ping time or Ping number or Water current distance. No schools are detected when the Distance mode is inconsistent with the Platform type. The choice of Distance mode value can affect SHAPES variables.

Specify school and candidate length and height extents under the Schools page of the EV File Properties dialog box (Press F6). It may be useful to use the Show time/distance grid to estimate horizontal school detection distances in units of meters/pings/seconds.

Detecting schools - post-processing

To detect schools over an entire echogram:

On the Echogram menu, click Detect Schools.
Enter the required settings on the Detect schools dialog box.
Click Detect.

To detect schools in a selection on an echogram:

Make a selection
On the Shortcut menu (right-click), click Detect Schools
Enter the required settings on the Detect schools dialog box.
Click Detect.

Warning: It is advised that schools regions shouldn't extend beyond the data. This may occur when you detect schools then remove data files and add new data such that schools regions extend beyond the new data. In this case, the calculation of inconsistent Uncorrected_length and Uncorrected_thickness may have undesired effects on other schools analysis variables. For more information refer to School Detection module algorithms.

Note: Changes to the Schools detection Properties or Variable Properties while a detection is running, results in the end of the detection and the start of a new detection.

Detecting schools while live viewing

To detect schools on new data arriving during live viewing:

On the Regions page of the Variable Properties dialog box, select Automatically detect schools during live viewing

- AND -

Begin live viewing from an echosounder using an Echolog application.

Note: Refer to the School detection while live viewing algorithm page for details on how schools are created while live viewing.

Classify regions after the detection

You can classify detected (school) regions using pre-specified Rules immediately after the school detection and after school detection while live viewing. For more information refer to Classify regions.

Export metrics

Export metrics (many not offered under on-screen analysis) include:

SHAPES variables licensed under the School Detection module.
Region analysis variables and Height_above_exclude_below line variables licensed under the Essentials module.