Nortek Power, Sv and TS

Echoview reads environmental, echosounder and values from the *.ad2cp file. Nortek echosounder equations are described in the:

Nortek Manual Principles of Operation 55 | 100 | 250 | 500 | 1000 kHz: Applications, Echo sounder
Nortek Manual Signature Integration 55 | 100 | 250 | 500 | 1000 kHz

Echoview uses the following equations and definitions:

Power

Nortek power equation

Sv

Nortek Sv equation

TS

Nortek TS equation

Where:

PrNortek
is Nortek Power (dB) = 0.01 dB * i

Where i is a signed integer value read from the data file.

R
is the sample range (m) calculated by the Nortek instrument, the calculation uses sample times and a nominal sound speed of 1500 ms-1.

α
is the absorption coefficient (dB m-1) of sea water. It is a function of acidity, depth, frequency, salinity, sound speed and temperature, and is calculated using the Francois & Garrison, 1982 equation.

The acidity (fixed at pH=8.1), frequency, salinity, sound speed and temperature are read directly from the data file. The depth (m) is a function of pressure, and is based on the equation in Fofonoff and Millard (1983). The equation is valid from 0 to 12000 dBars and excludes the geopotential anomaly correction:

AbsorptionDepth = (9.72659P - 2.2512×10-5P2 + 2.279×10-10P3 - 1.82×10-15P4)/(g + 0.5γP)

Where:

P = Pmeasured - GETUSER,POFF + 10.13 dBar

(Pmeasured and GETUSER,POFF are read from the data file. Refer to the DF3 Burst/Average section of the Nortek Integration manual.)

g = 9.8 ms-2

γ = 2.226×10-6 ms-2 dBar-1

The AbsorptionDepth, Acidity, Frequency, Salinity, SoundSpeed and Temperature can be found on the Calibration page of the Variable Properties dialog box.

PL
is the Nortek configured transmit power level (dB) stored in the file header section of the data file. Using Nortek instrument power level scaling, the dB value can be converted to Watts.

TransmittedPower (W) is displayed on the Calibration page of the Variable Properties dialog box.

c
is the sound speed (ms-1). Nortek sound speed is nominally 1500 ms-1.

Ψ
is the TwoWayBeamAngle (dB re 1 sr) and is calculated at specific frequencies using the values recorded under the Nortek calibration polynomials in the data file. Refer to GETUSERECHOTWOWAYANGLE in the Nortek Integration manual.

τ
is the Nortek configured transmit pulse length (ms) recorded in the Nortek data file header.

The value for τ is assigned to PulseDuration on the Calibration page of the Variable Properties dialog box.

CalibrationOffsetSv
and
CalibrationOffsetTs
The calibration offset terms are frequency-dependent gain corrections (dB) determined from calibration sphere measurements, or other methods.

Echoview searches the data file for the frequency-gain pairs. If these are not found, the gains are derived from a polynomial function instead. (Refer to the section 5.56 Echosounder gain calibration in the Nortek Integration manual.)

If neither the pre-calculated frequency-gain pairs nor the coefficients are found in the data file, no calibration offset terms are added.

Specifying the CalibrationOffsetSv or CalibrationOffsetTs in an ECS file overrides the default values.

PrNortek	is Nortek Power (dB) = 0.01 dB * i Where i is a signed integer value read from the data file.
R	is the sample range (m) calculated by the Nortek instrument, the calculation uses sample times and a nominal sound speed of 1500 ms-1.
α	is the absorption coefficient (dB m-1) of sea water. It is a function of acidity, depth, frequency, salinity, sound speed and temperature, and is calculated using the Francois & Garrison, 1982 equation. The acidity (fixed at pH=8.1), frequency, salinity, sound speed and temperature are read directly from the data file. The depth (m) is a function of pressure, and is based on the equation in Fofonoff and Millard (1983). The equation is valid from 0 to 12000 dBars and excludes the geopotential anomaly correction: AbsorptionDepth = (9.72659P - 2.2512×10-5P2 + 2.279×10-10P3 - 1.82×10-15P4)/(g + 0.5γP) Where: P = Pmeasured - GETUSER,POFF + 10.13 dBar (Pmeasured and GETUSER,POFF are read from the data file. Refer to the DF3 Burst/Average section of the Nortek Integration manual.) g = 9.8 ms-2 γ = 2.226×10-6 ms-2 dBar-1 The AbsorptionDepth, Acidity, Frequency, Salinity, SoundSpeed and Temperature can be found on the Calibration page of the Variable Properties dialog box.
PL	is the Nortek configured transmit power level (dB) stored in the file header section of the data file. Using Nortek instrument power level scaling, the dB value can be converted to Watts. TransmittedPower (W) is displayed on the Calibration page of the Variable Properties dialog box.
c	is the sound speed (ms-1). Nortek sound speed is nominally 1500 ms-1.
Ψ	is the TwoWayBeamAngle (dB re 1 sr) and is calculated at specific frequencies using the values recorded under the Nortek calibration polynomials in the data file. Refer to GETUSERECHOTWOWAYANGLE in the Nortek Integration manual.
τ	is the Nortek configured transmit pulse length (ms) recorded in the Nortek data file header. The value for τ is assigned to PulseDuration on the Calibration page of the Variable Properties dialog box.
CalibrationOffsetSv and CalibrationOffsetTs	The calibration offset terms are frequency-dependent gain corrections (dB) determined from calibration sphere measurements, or other methods. Echoview searches the data file for the frequency-gain pairs. If these are not found, the gains are derived from a polynomial function instead. (Refer to the section 5.56 Echosounder gain calibration in the Nortek Integration manual.) If neither the pre-calculated frequency-gain pairs nor the coefficients are found in the data file, no calibration offset terms are added. Specifying the CalibrationOffsetSv or CalibrationOffsetTs in an ECS file overrides the default values.

Nortek Power, Sv and TS

Power

Sv

TS

See also