Single target detection single beam

Method 1

This operator detects single targets using the algorithm implemented by Simrad in the EK500 echosounder.

Echoview accepts a single operand of TS data type as input.

For algorithm information see Single beam (method 1).

Note: Prior to Echoview 4.30, this operator also accepted the Sv data type as input. Sv data requires a Sv to TS conversion and appropriate calibration settings. To avoid confusion and incorrect data, this operator has been simplified. EV files with old versions of the operator will appear with [deprecated] in the operator name and behave as they previously did.

Method 2

This operator detects single targets from single beam data using an algorithm based on Echoview Software's understanding of the single target detection algorithm implemented by Simrad in the EK60 echosounder.

Echoview accepts a single operand of TS data type as input.

For algorithm information see Single beam (method 2).

Settings

The Single Target Detection Single Beam (Method 1 or Method 2) Variable Properties dialog box pages include (common) Variable Properties pages and these operator pages:

Operands page

Filter Targets page

Single Target Detection page

Single target detection parameters

Setting

Description

TS threshold (dB) (uncompensated TS)

Represents the uncompensated TS of the smallest single target of interest to you. Determine what TS you are interested in (the TS for fish rather than the TS for plankton) and set TS threshold to a value that is a bit smaller. 

The minimum value for this setting is -120 dB re 1m2. This minimum value will detect spike noise, especially if you also use a short minimum pulse length.

Single beam target detection Method 1 and Method 2 operators apply an uncompensated TS threshold. Beam compensation is unavailable to both operators and as a result uncompensated TS is identical to compensated TS.

Pulse length determination level (dB)

This is theoretically and in-practice 6 dB (and rarely changed).

PLDL is calculated relative to the pulse's TS peak. Samples above the PLDL are included in the detection. Normalized pulse length and Standard deviation of angles are based on included samples.

Minimum normalized pulse length

Minimum normalized pulse length together with Maximum normalized pulse length are used to reject pulses that fail the estimate for expected echo length.

Too short a pulse length allows too many false detections. Too long a pulse length allows the loss of too many real detections. (Pers. comm. I. Higginbottom).

The minimum value is 0.01.

EK60

Samples are separated by 1/4 pulse length. Apparent Echoview normalized lengths will be 0.25, 0.5, 0.75, 1, 1.25 , 1.5. These values are due to Simrad's sampling and the fact that Echoview does not interpolate.

  • Typically a 0.7 minimum normalized pulse length results in three samples in a pulse.
  • 1.3 results in 5 samples in a pulse.
  • Over 1 and  less than 1.25 results in only 4 samples, which is one normalized pulse.
BioSonics

BioSonics data has many more samples in a pulse. The estimate for echo length is not as constrained as for Simrad data.

Maximum normalized pulse length

Minimum and Maximum normalized pulse length are used to reject pulses that fail the estimate for expected echo length. See Minimum normalized pulse length.

Too short a pulse length allows the loss of too many real detections. Too long a pulse length allows too many false detections. (Pers. comm. I. Higginbottom).

The maximum value is 10.

Exclusion

The Exclusion section is used to select lines to limit targets and minimize processing.

Setting

Description

Exclude targets above line

These are analogous to the Exclude-above and Exclude-below lines used on the Analysis page.

The exclusions on the Single target detection page are applied before the echogram is displayed (affecting the number of targets displayed) and the exclusions on the Analysis page are applied after the echogram is displayed (affecting the on-screen and exported analyses). See About setting variable properties for an illustration of which pages apply when.

Exclude targets below line

The correct configuration of calibration settings (environment and echosounder system) and transducer geometry for the operands is important. You may need to configure raw variables prior to using the operator. For more information refer to Creating single target detection variables from single beam data.

If you are familiar with Single target detection (or TS-Detection) on Simrad echosounders, see Simrad and Echoview single target detection terminology for a comparison of the terms used.

See also

About virtual variables
Operator licensing in Echoview
Tuning single target detection