Single Target Detection - Wideband

This operator detects single targets using a modified version of the single target detection split beam (method 2) algorithm applied to pulse compressed complex TS and pulse compressed complex angular position data.

Note: Detected single targets may be affected by factors that can degrade the wideband frequency response.

Echoview accepts operands of the following data types as input:

Operand 1

Operand 2

  • Pulse compressed complex TS
  • Pulse compressed complex angular position

For algorithm information see Single target detection - wideband.

This single target operator is under active development in collaboration with Simrad and the hydroacoustic community. The operator is based on a split beam method 2 algorithm where the TS Threshold is applied to compensated TS.

Settings

The Single Target Detection Wideband Variable Properties dialog box pages include (common) Variable Properties pages and these operator pages:

Operands page

Filter Targets page

Single Target Detection page

General parameters

Setting

Description

TS threshold (dB) (compensated TS)

Simrad LOBE beam compensation has been selected, the operator applies a compensated TS threshold to data after detection occurs.

Compensated TS threshold represents the compensated 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 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.

For further information about Simrad EK80 data and the Simrad LOBE model refer to Simrad LOBE used by Simrad EK80 pulse compressed data.

Pulse length detection 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).

Pulse compressed wideband operands use the PulseCompressedEffectivePulseLength for normalization calculations.

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).

Pulse compressed wideband operands use the PulseCompressedEffectivePulseLength for normalization calculations.

Minimum target separation

Minimum target separation is used to filter out targets that are separated by less than the Minimum target separation value. This is useful for high resolution pulse compressed operands, where one single target may be more helpful than many closely spaced single targets of the same water column feature.

Beam compensation

Setting

Description

Beam compensation model

Available settings are:

Beam compensation modeling for a frequency modulated transmit pulse is a topic in active development. Beam patterns can be modeled and can be used to estimate what the TS value would be if the target was central in the beam.

Echoview calculates frequency dependent Simrad LOBE beam compensation using values read from the data file. Within the bandwidth of the transmitted pulse, values are interpolated. For frequencies outside the bandwidth, the closest valid value is used. See also Simrad EK80: Frequency dependent limitations.

The Simrad LOBE model is valid over the range 0 to 12 dB.

Maximum beam compensation (dB)

Beam patterns can be modeled and can be used to estimate what the TS value would be if the target was central in the beam.

Higher values of beam compensation result in more single targets. Many beam compensation models cite limits of validity.

The maximum value is 35 dB (split beam and dual beam only).

A color matched Maximum beam compensation line for a target may be displayed on the Wideband frequency response graph. See also: Graph Properties settings.

Note: The value for Maximum beam compensation is important when using the export variables Beam_volume_sum and Wedge_volume_sampled. For further information refer to Beam angle parameters.

Exclusion

Setting

Description

Maximum standard deviation
(both minor and major axis angles)

Applies to samples in the  single target peak as specified by the Minimum and Maximum normalized pulse lengths.

The standard deviation of minor and major axis angles relates back to angular position and where the target is in the beam. When there is more than one target then phase is noisy and TS is not accurate. Use Maximum standard deviation settings to limit noise with respect to phase or in cases of low signal to noise. As Maximum standard deviation is increased more false detections may occur.

"... Phase-jitter (angle standard deviation) should be smaller than a certain value... " (Parker-Stetter et al: Section 9.2 Single-echo detection).

 

The maximum value is 45 degrees (split beam only). The maximum value for this setting effectively means the detection ignores the angle deviation. (Pers. comm. I. Higginbottom).

Line Exclusion

The Line 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 wideband 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.

Algorithm

Algorithm

See also

About virtual variables
Operator licensing in Echoview
Tuning single target detection