TVG range correction algorithms

A TVG range correction algorithm can be specified for the TvgRangeCorrection calibration setting on the Calibration page of the Variable Properties dialog box. Use an ECS file to modify the setting.

The purpose of TVG range correction is to correct for the introduced errors from nominal TVG and apply TVG at the correct range, particularly for data collected at short ranges. If your data is located in the transition from near field to far field conditions (short ranges), then the application of TVG at the correct range becomes important. Using TVG range correction for Sv and TS data helps to minimize error for further calculations such as the estimation of biomass.

TVG range correction is also important in the choice of Echoview single target detection method for your data. For more information refer to About Time Varied Gain: TVG range correction and Principles of TVG range correction and Sv data.

See also Using a SoundSpeedProfile: Notes, Near-field depth estimation virtual line.

Algorithms include:

Algorithm applicable to Sv or TS variable	Algorithm applicable to Sv variable only
None
BySamples	SimradEx60
PulseLength	Biosonics, Kaijo, SimradEK80
Ex500Forced	SimradEx500
	Standard

Notes:

• Some variables will use a variable-specific algorithm (default setting) as determined by the data. For more information refer to Common calibration names: TvgRangeCorrection.
• The TvgRangeCorrection setting allows you to specify the TVG range correction algorithm applied to a Sv or TS variable. Use an ECS file to change the setting.
• Changes in calibration settings used for range calculations may shift ping data in the depth dimension but will not automatically adjust the position of regions and lines. You should review any existing regions and lines to ensure they are still valid. For more information refer to Range calculation effects on regions and lines.

None

When None is selected for the TvgRangeCorrection setting the following algorithms are applied:

Sv variable or TS variable

No TVG range correction is applied to the variable.

BySamples

When BySamples is selected for the TvgRangeCorrection setting the following algorithms are applied:

Sv variable or TS variable

R = r - s*T Where: R is the corrected range (m) r is the uncorrected range (m) s is the value specified by the TvgRangeCorrectionOffset (samples) T is the sample thickness (m). It may also be calculated as half the sound speed divided by the sampling frequency.

SimradEx60

When SimradEx60 is selected for the TvgRangeCorrection, the Standard algorithm is applied in the following way:

Sv variable only

R = r - cτ/4 Where: R is the corrected range (m) r is the uncorrected range (m) c is the sound speed (m/s) (SoundSpeed on the Calibration page of the Variable Properties dialog box) τ is the TransmittedPulseDuration (s) on the Calibration page of the Variable Properties dialog box

Notes:

• SimradEx60 applies no offset for TS variables, as advised under Simrad time Varied Gain Range Correction.
• From Echoview 11 onward SimradEx60 TvgRangeCorrection ceased to use the BySamples Sv algorithm with a TVG range correction offset of 2 samples. It was observed that the assumption where exactly 2 samples equals cτ/4 could become invalid when Simrad Ex60 data is resampled. See also Changes to Simrad Ex60 sample range calculation in Echoview.

Ex500Forced

Sv variable or TS variable

R = r - (3 * T + τ * 1470 / 4) Where: R is the corrected range (m) r is the uncorrected range (m) Τ is the sample thickness (m). It may also be calculated as half the sound speed divided by the sampling frequency. τ is the Transmitted pulse duration (s) 1470 is the sound speed used by Simrad (m/s)

SimradEx500

When SimradEx500 is selected for the TvgRangeCorrection setting the Ex500Forced algorithm is applied in the following way:

Sv Wn variable only

R = r - (3 * T + τ * 1470 / 4)

PulseLength

Sv or TS variable

R = r - cτ /4 Equation definitions

Biosonics

When Biosonics is selected for the TvgRangeCorrection setting the PulseLength algorithm is applied in the following way:

Sv variable only

R = r - cτ/4 Equation definitions

Kaijo

When Kaijo is selected for the TvgRangeCorrection setting the PulseLength algorithm is applied in the following way:

Sv variable only

R = r - cτ/4 Equation definitions

SimradEK80

When SimradEK80 is selected for the TvgRangeCorrection setting the PulseLength algorithm is applied in the following way:

Sv variable only

R = r - cτ/4 Equation definitions

Standard

Exported Echoview Data File Format data is assigned the following TvgRangeCorrection setting.

Sv variable only

R = r - cτ/4 Equation definitions

See also

About time varied gain