Single target detection - dual beam (method 1) algorithm

This operator applies a superset of the Single beam (method 1) algorithm (Soule et al., 1995, 1996, 1997, Ona et al., 1999), adding beam compensation estimates to the peak selection criteria.

See Single target pulse properties for illustrations on how target TS and normalized pulse lengths are determined. The page also offers an illustration of a single target pulse with respect to single beam detection settings.

Refer to Single Target detection algorithms for information about the method that best suits your data.

Variable properties

The first operand must be a TS variable for the narrow beam channel. The second operand must be a TS variable for the wide beam channel.

Each operand must have been associated with a different transducer and the 3dB beam width settings must have been be defined for each variable.

Hint:  You associate a transducer with a variable on the Calibration page of the Variables properties dialog box and enter 3dB beam angles on the Calibration page of the Variable Properties dialog box.

It is left to you to select which TS variables correspond to the same dual-beam transducer.

The following Single Target detection settings are used in the algorithm (which is a superset of the single beam (method 1) algorithm, additions being indicated in red.):

Parameter

Unit

Allowed range

Default value

TS threshold

dB re 1m2

-120 - 20

-50

Pulse length determination level (PLDL)

dB re 1m2

0.01 - 30

6

Minimum normalized pulse length

-

0.01 - 10

0.7

Maximum normalized pulse length

-

0.01 - 10

1.5

Maximum beam compensation

dB

0 - 35

4.0

Over axis angle threshold

dB

-99.9-0

-1

The single target detection parameters are set on the Single Target Detection page of the Variable Properties dialog box. Lines can also be selected for excluding targets above or below a line. Apart from limiting the target detection range, exclusions will also speed up processing, since less data will then be screened for single targets.

Notes:

Algorithm

Echoview detects dual-beam single targets as follows:

  1. Echoview performs a single target detection (using the Single target detection - single beam method 1 algorithm) on both the narrow-beam and wide-beam channels.

  2. For each single target on the narrow-beam channel (working from nearest range to farthest range)

2.1   The closest single target on the wide-beam channel is identified.
Note:
Single targets on the wide-beam channel are not considered if: they have already been matched to a single target on the narrow-beam channel; or they have a range that is less than the range of a single target that has been matched to a single target on the narrow-beam channel.

2.2   Beam compensation is calculated for the dual-beam single target (see Beam compensation BioSonics dual beam).

2.3   The following values (among others) are assigned to the dual-beam single target detection.

Single target properties

The table below describes how algorithm specific single target properties are calculated. See About analysis variables for a complete list of single target properties

Analysis variable

Unit

Description

TS_uncomp

dB re 1m2

TS of the single target on the narrow-beam channel (as determined by Single target detection - single beam method 1 followed by the dual beam Steps 2.1 and 2.2).

See Step 2.3 of this algorithm.

TS_comp dB re 1m2

Compensated TS of the single target.

See Step 2.3 of this algorithm.

Target-range

m

Range of the single target on the narrow-beam channel

Angle-minor axis

degrees

Not available for targets detected using this algorithm

Angle-major axis

degrees

Not available for targets detected using this algorithm

Note: The number of targets detected by the Dual beam (method 1) operator will always be less than or equal to the number of targets detected by the Single beam (method 1) operator. This is because the Dual beam (method 1) operator employs the same algorithm above, but the pulses must pass beam compensation criteria as well before being accepted.

See also

About Single target detection
Single target detection algorithms

Echoview and Simrad algorithms

References

Single target pulse properties