Track Detection Properties dialog box

The Track Detection Properties dialog box is used to enter the settings that will be used for the fish track detection process.

To display the Track Detection Properties dialog box either:

  1. Display the EV File Properties dialog box.

  2. Click the Fish Tracks tab.

  3. Click Track Detection Properties.

- OR-

  1. Display the Detect Fish Tracks dialog box.

  2. Click Properties.

There are three pages on the Track Detection Properties dialog box:

Each page represents a stage in the fish track detection process. See Fish tracking algorithms for a more detailed description of the processes followed in Echoview.

Algorithm page

The Algorithm page of the Track Detection Properties dialog box is used to identify which single targets are candidates for adding to a track.

Data

The Data section is used to choose one of two algorithms available for fish track detection.

Settings

Description

2D (range and time)

Choose this option if your data is from a single beam or dual beam echosounder.

You can also choose this option if you want the detection to disregard the angles in split beam data; all targets will be treated as if they were at the center of the beam.

4D (range, angles and time)

Choose this option if your data is from a split beam echosounder and you want the angle data to be used in the detection.

Track detection

The settings in the Track detection section are used to determine a predicted location for the next target in a track. This predicted location is compared to the observed location of each target to determine whether the target should be considered as a candidate for the track.

Settings

Description

Alpha

Gain settings that define the algorithm's sensitivity to unpredicted changes in position (that is, speed of the target).

Lower Alpha values are less sensitive to measurement noise, higher Alpha values are more responsive to target movements.

Beta

Gain settings that define the sensitivity to unpredicted changes in velocity (that is, changes in direction and/or speed of a target).

Lower Beta values are less sensitive to measurement noise, higher Beta values are more responsive to target movements.

Velocity is generally more sensitive to noise than position and Beta is generally lower than Alpha.

Tip:   For a target that swims or travels in a highly predictable fashion low gain values should be set. Conversely, the more erratic the target's swimming behavior the larger the gain settings that are required.

See About beam geometry for a description of the axes.

Target gates

The settings under Target gates are used to determine whether the observed location of a target is close enough to the predicted location for the target to be considered as a candidate.

Settings

Description

Exclusion distance (m)

Choose distance(s) around the predicted location within which a target must be located in order to be a candidate. 

Hint: The Exclusion distance should be of the same order of magnitude as the expected changes in position.

Missed ping expansion (%)

Increases the exclusion distances for each missed ping between the last target in the track and the current ping. The expansion is linear (or arithmetic) for successive missed pings.

To disable the missed ping expansion, accept the defaults of zero.

For 2D fish track detection, the difference in range between the predicted and observed location of the target must be within the Range target gate.

For 4D fish track detection, the settings are used to create a volume around the predicted location within which the observed location must fall. See About beam geometry for a description of the axes.

Note: Target gate = Exclusion distance + N x (Exclusion distance x missed ping expansion/100), where N is the number of missed pings.

Weights page

The Weights page of the Track Detection Properties dialog box is used for the weighting and allocation of single target candidates to a track.

Once a single target is identified as a candidate for a track, a measure of its suitability as a candidate for the track is determined by considering the weights of particular "track to target" differences.

The effect of the individual weights on the allocation process is determined by their relative magnitude.

Setting

Description

Major axis

Weighting for the difference between the predicted location and the observed location of the target along the major axis.

Weighting is a number between 1-100.

Minor axis

Weighting for the difference between the predicted location and the observed location of the target along the minor axis.

Weighting is a number between 1-100.

Range

Weighting for the difference between the predicted location and the observed location for the range of the target.

Weighting is a number between 1-100.

TS

Weighting for the difference between the Target Strength of the last target in the open track and the observed target.

Weighting is a number between 1-100.

Ping gap

Weighting for the ping gap difference between the last target in the open track and the observed target location.

Weighting is a number between 1-100.

Notes:

See Fish tracking algorithms for more details of these calculations.

Track Acceptance page

The Track acceptance page of the Track Detection Properties dialog box is used for the acceptance of tracks against a set of track criteria.

Setting

Description

Minimum number of single targets

Fish tracks that do not meet all of these criteria will not be included in the final fish track detection.

Minimum number of pings

Maximum gap between single targets

See also

About fish track detection
Fish tracking algorithms

About beam geometry