Filter Targets page

The Filter Targets page is displayed on the Variable Properties dialog box for:

When a "target" variable is in focus, the Filter Targets page can be used to filter targets from the echogram. Targets that do not satisfy the filter criteria will not be displayed in the echogram or included in any analyses.

Settings

Description

Filter angles

Select this check box to specify values for the minimum and maximum angles allowed for single targets.

Note: These values are inclusive, so that specified values are included within the display.

Minor-axis angle - Minimum

Enter an angle, in degrees, to specify the minimum angle for the minor beam axis.  This must be between -90 and -0.01 degrees.

Minor-axis angle - Maximum

Enter an angle, in degrees, to specify the maximum angle for the minor beam axis.  This must be between 0.01 and 90 degrees.

Major-axis angle - Minimum

Enter an angle, in degrees, to specify the minimum angle for the major beam axis.  This must be between -90 and -0.01 degrees

Minor-axis angle - Maximum

Enter an angle, in degrees, to specify the maximum angle for the major beam axis.  This must be between 0.01 and 90 degrees.

Filter beam compensation

Select this check box to enter and apply a Maximum beam compensation in dB.

Filter pulse length at 6 dB (normalized)

Select a check box to specify minimum and maximum values for the normalized pulse length of single targets.

A single target echo usually has a normalized pulse length of 1.0 ± 0.5 at 6 dB down from the PLDL.

The Filter pulse length at 6 dB setting can be used to filter out spike noise from imported single target data.

The Filter settings may be used to filter spike noise from echogram data. Spike noise is not a true reflection of the transmit pulse and is more likely to have a non-standard pulse shape. Similarly, the normalized pulse length for spike noise is likely to be non-standard.

There are two scenarios where the 12 dB and 18 dB pulse length filters may be useful:

  1. For filtering out echo traces within schools. Often these are actually echoes from individual fish, but the proximity of other fish within the school makes the TS unreliable, so the user wants to filter them out. If a fish is within a school then often its echo has a sensible shape at 6 dB but the background school echo takes over at 12 dB and/or 18 dB.
  2. For filtering out spike noise in general, whether in schools or not. While the main 6dB pulse filter will exclude most spikes, the 12 dB and/or 18 dB filter might help to remove spikes that register a sensible pulse length at 6 dB.

See also: An example of a single target pulse in relation to single target detection settings.

Filter pulse length at 12 dB (normalized)

Filter pulse length at 18 dB (normalized)

See also

About virtual variables
Operators

Variable Properties dialog box