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.

-OR-

the TVG Range correction method on the TS TVG Correction settings for the Minimum TS threshold section on the Data page of the Variable Properties dialog box

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	Variable-specific counterpart of the algorithm
None
BySamples	SimradEx60
PulseLength	Biosonics, Kaijo
Ex500Forced	SimradEx500

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 an Sv or TS variable. Use an ECS file to change the setting.

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 setting the BySamples algorithm is applied in the following way:

Sv variable only

The BySsamples Sv algorithm is used with a TVG range correction offset of 2 samples.

Ex500Forced

Sv variable or TS variable

R = r - (3 * T + t * 1470 / 4)

where:

R
is the corrected range (m)

r
is the uncorrected range (m)

T
is the sample thickness (m).

It may also be calculated as half the sound speed divided by the sampling frequency.

t
is the Transmitted pulse length (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 + t * 1470 / 4)

PulseLength

Sv or TS variable

R = r - ct /4

where:

R

is the corrected range (m)

r
is the uncorrected range (m)

c
is the sound speed (m/s) on the Calibration page of the Variable Properties dialog box.

t
is the Transmitted pulse length (s) on the Calibration page of the Variable Properties dialog box.

Biosonics

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

Sv variable only

R = r - ct /4

Kaijo

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

Sv variable only

R = r - ct /4

TVG range correction algorithms

None

BySamples

SimradEx60

Ex500Forced

SimradEx500

PulseLength

Biosonics

Kaijo

See also