About layered TVG

In traditional acoustics the time varied gain (TVG) is typically of the following form:

20 log(r) + 2ar		for Sv calculation (dB)
40 log(r) + 2ar		for Sp (or TS) calculation (dB)

where:

r is the range of a sample (m)
a is the absorption coefficient (dB/m)
log(r) is the base 10 logarithm of r

These TVG functions however are based on the key assumption of free spherical spreading. This assumption is known to break down in certain environments.

For this reason it may be appropriate to apply a TVG function which is layered and ensures continuous magnitude values of the incident sound pressure at layer boundaries. Echoview currently provides such a facility for some Furuno FSV variables only.

Note: Echoview provides the facility to apply a layered TVG, but cannot suggest the most appropriate TVG for your application. This is an experimental feature for an evolving area in the field of hydroacoustics.

Furuno FSV Layered TVG

We define:

where:

p' r
is the value of a sample in the magnitude variable, representing received (or incident) sound pressure (μPa)

p r
is the recorded value of received sound pressure for a sample in the low or high resolution data block of the .fsv file (μPa)

g
is the recorded value of gain for a sample in the low or high resolution TotalGain block of the .fsv file (μPa)

r
is the range of the sample (m)

g(r)
where 0 ≤ r < 1

where 1 ≤ r < r1 (Near layer)

where r1 ≤ r < r2 (Meduim layer)

where r2 ≤ r (Far layer)

g0
is the transducer gain recorded as the first element of the low or high resolution TotalGain block of the .fsv file – that is, g at range 0 (μPa)

Dg
is the linear value of the FurunoFsvTvgOffsetGain on the Calibration page of the Variable Properties dialog box (-)

TVGn
is the value of FurunoFsvTVGFactorNear, FurunoFsvTVGFactorMedium, FurunoFsvTVGFactorFar layer respectively on the Calibration page of the Variable Properties dialog box (dB)

rn
is the value of FurunoFsvTVGStartRangeMedium, FurunoFsvTVGStartRangeFar layer respectively on the Calibration page of the Variable Properties dialog box (m)

X

Y

p' r	is the value of a sample in the magnitude variable, representing received (or incident) sound pressure (μPa)
p r	is the recorded value of received sound pressure for a sample in the low or high resolution data block of the .fsv file (μPa)
g	is the recorded value of gain for a sample in the low or high resolution TotalGain block of the .fsv file (μPa)
r	is the range of the sample (m)
g(r)		where 0 ≤ r < 1
		where 1 ≤ r < r1	(Near layer)
		where r1 ≤ r < r2	(Meduim layer)
		where r2 ≤ r	(Far layer)
g0	is the transducer gain recorded as the first element of the low or high resolution TotalGain block of the .fsv file – that is, g at range 0 (μPa)
Dg	is the linear value of the FurunoFsvTvgOffsetGain on the Calibration page of the Variable Properties dialog box (-)
TVGn	is the value of FurunoFsvTVGFactorNear, FurunoFsvTVGFactorMedium, FurunoFsvTVGFactorFar layer respectively on the Calibration page of the Variable Properties dialog box (dB)
rn	is the value of FurunoFsvTVGStartRangeMedium, FurunoFsvTVGStartRangeFar layer respectively on the Calibration page of the Variable Properties dialog box (m)
X
Y

About layered TVG

Furuno FSV Layered TVG

See also