EK80 Power, Power to Sv and TS

CW data
FM data

CW data

Echoview extracts Power (dB re 1 W) raw variables from EK80 data files.

The "CW" instrument configuration records data returned under a single frequency transmit pulse.

Echoview derives two raw variables from power data:

Power

Power variables on the Filesets window represent the Received power (dB) which is calculated from the raw power, number of transducer segments and transceiver impedance read from the data file.

Calculation of Sv and TS

The Sv and TS values are calculated from the raw power data according to:

where:

R = the corrected range (m) - see TVG Range Correction

Pr = received power (dB re 1 W)

Pt = transmitted power (W)

α = absorption coefficient (dB/m)

G0 = transducer peak gain (non-dimensional)

Echoview calculates G0 = 10^(G'0/10) where:

G'0 is calculated by looking up the value from GainTableWideband at the Center frequency (kHz). When available, GainTableWideband may be viewed on the Calibration page of the Variable Properties dialog box. When GainTableWideband is unavailable, G'0 is calculated by:

G'0 = G''0 + 20log (f/fnominal)

Where:

G''0 is the TransducerGain (dB) on the Calibration page of the Variable Properties dialog box. This value should be the same for TS and Sv variables and equal to the Transducer gain specified under Ping (from file) of the Details dialog box.

f is the Center frequency (Hz). See below.

fNominal is the Nominal frequency represented by Frequency in Hz on the Calibration page of the Variable Properties dialog box.

λ = wavelength (m) = c/f

f = Center frequency (Hz)

Echoview calculates f = (fS +fE)/2 where:

fS is the FrequencyStart (kHz) and fE is the FrequencyEnd (kHz) on the  Calibration page of the Variable Properties dialog box.

For CW data, the Center frequency (Hz) is the Frequency on the Calibration page of the Variable Properties dialog box.

c = sound speed (m/s) entered on the  Calibration Page of the Variable Properties dialog box.

τ = pulse duration (s). CW Sv, FM Sv and pulse compressed Sv use appropriate versions of this quantity. See Notes below.

ψ = Equivalent Two-way beam angle (Steradians) defined as the beam width at the Center frequency.

Echoview calculates ψ = 10^((Ψ'+ 20*log(fNominal/f))/10), where:

Ψ' is the Two-way beam angle (dB re 1 Steradian) on the Calibration Page of the Variable Properties dialog box.

fNominal is the Nominal frequency and is the Frequency on the Calibration page of the Variable Properties dialog box.

f is the Center frequency (Hz), see above.

Sa correction= Simrad correction factor (dB re 1m-1) determined during calibration of the EK80. Its value represents the correction between the ideal pulse the system is trying to generate, and the actual pulse. It corrects for limitations in the hardware.

 

Notes:

FM data

Echoview calculates Received Power (dB re 1 W) from raw power, the number of transducer segments and transceiver impedance read from EK80 data files. The "FM" instrument configuration records data returned under a frequency modulated transmit pulse (chirp).

Echoview derives these raw variables from power data:

Calculation of Sv and TS

Echoview can read frequency dependent information from the data file and interpolates values for transducer gain, beam width, frequency and Simrad LOBE beam compensation as required. See also Simrad EK80: Frequency dependent limitations. When frequency dependent data is unavailable, equations that use relationships based on a nominal frequency are used.

Wideband variables

The Sv and TS values are calculated from the raw power data using equations similar in form to the EK80 CW equations. The transmitted pulse characteristics of the chirp are used to calculate transducer constants. Echoview reads temperature, acidity and salinity from the Simrad EK80 data file and uses the Francois & Garrison (1982) equation to calculate absorption coefficients for TVG. The Simrad EK80 'Ramping' for the chirp is included in calculations. For further details about the EK80 wideband power to Sv and TS equations contact Simrad.

The EK80 Sv represents the Sv for the chirp. The EK80 TS represents the TS for the chirp. The values are analogous to Sv or TS for a single frequency.

Note: Wideband Sv data is calculated using using EffectivePulseLength instead of TransmittedPulseLength.

Pulse compressed wideband variables

Wideband data is pulse compressed by a matched filter convolution. The matched filter is based on the transmitted pulse. Pulse compressed wideband Sv is calculated using PulseCompressedEffectivePulseLength. For further details about the EK80 wideband power to Sv and TS equations contact Simrad.

EK80 pulse compressed Sv represents the pulse compressed Sv for the chirp. EK80 pulse compressed TS represents the pulse compressed TS for the chirp.

Note: Pulse compressed wideband Sv is calculated using PulseCompressedEffectivePulseLength instead of TransmittedPulseLength.

To extract useful single frequency information from pulse compressed data it is advised to analyze the TS data of a single target. To do this, Echoview offers:

See also

Simrad EK80 file format
Raw variables derived from Simrad EK80 data
Calibration settings for Simrad EK80 data
About transmitted pulses