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.

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:

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 SoundSpeed (m/s) on the Calibration page of the Variable Properties dialog box.
τ
is the TransmittedPulseLength (s) on the Calibration page of the Variable Properties dialog box.

Notes:

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