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
Sv
TS
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) of sea water. It is a function of acidicy, 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 (meters) 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-2dBar-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 1sr) and is calculated at specific frequencies using the values recorded under the Nortek calibration polynominals 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
CalibrationOffsetTsThe calibration offset terms are freqency-dependant gain corrections (dB) determined from calibration sphere measurements, or other methods.
Echoview searches the data file for the frequency-gain pairs. If these not found, the gains are derived from a polynomial function instead. (Refer to GETUSERECHOTWOWAYANGLE in the Nortek Integration manual.)
Specifying these in an ECS file overrides the default values.
See also
Nortek file format
Raw variables derived from Nortek data files
Calibration settings for Nortek data