Simrad EK80 Power, Power to Sv and TS

Echoview derives power (dB re 1 W) raw variables from EK80 data files. Power variables on the Filesets window represent the received power which is calculated from the raw power, number of transducer segments and transceiver impedance read from the data file.

Continuous wave (CW) data
Frequency modulated (FM) data
EK80 EC150-3C data

Continuous wave (CW) data

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

Echoview derives two raw variables from power data from each transducer segment (T1, T2,... Tt):

Sv raw pings Tt
TS raw pings Tt

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

r = the uncorrected range (m)

Pr = received power (dB re 1 W)

Pt = transmitted power (W)

α = absorption coefficient (dB/m). CW variables can use a calculated value for AbsorptionCoefficient. The calculated value can be overridden by the AbsorptionCoefficient specified in an ECS file.

G0 = transducer peak gain (non-dimensional). Echoview calculates G0 as 10^(G'0/10) from:

, 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). For CW data, this is the Frequency on the Calibration page of the Variable Properties dialog box.

fnominal is the nominal frequency (Hz) represented by Frequency on the Calibration page of the Variable Properties dialog box. Note: there are instances when f = fnominal which would render G'0 = G''0.

λ = c/f = wavelength (m) at f

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

τ = pulse duration (s). For CW data, this is calculated using EffectivePulseDuration. CW data recorded as non-complex data may use the TransceiverSamplingFrequency to calculate the EffectivePulseDuration.

ψ = equivalent two-way beam angle (steradian) defined as the beam width at f. Echoview calculates ψ as 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 (Hz) represented by Frequency on the Calibration page of the Variable Properties dialog box.

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

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 is specified as the SaCorrectionFactor on the Calibration page of the Variable Properties dialog box.

Notes:

EK80 TVG range correction is only applied to Sv data.

Sv TVG range correction is calculated using TransmittedPulseDuration.

CW Sv calculations for the -10 log [cτψ/2] term support Soundspeed-Depth data. See also: Using sound speed profile data.

CalibrationOffset is added to the Sv equation when it is read from an ECS file or included in a data file.

CalibrationOffset is added to the TS equation when it is read from an ECS file or included in a data file.

Frequency Modulated (FM) data

The FM instrument configuration records data returned under a frequency modulated transmit pulse (chirp).

Echoview derives these raw variables from power data from each transducer segment (T1, T2,... Tt):

Sv wideband pings Tt

TS wideband pings Tt

Sv pulse compressed wideband pings Tt

TS pulse compressed wideband pings Tt

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 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 Sv and TS values are calculated from the raw power data using these equations:

where:

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

r = the uncorrected range (m)

Pr = received power (dB re 1 W)

Pt = transmitted power (W)

α = absorption coefficient (dB/m)

fc = center frequency (Hz). Echoview calculates fc = (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.

λfc = c/fc = wavelength (m) at fc

τeff = the EffectivePulseDuration on the Calibration page of the Variable Properties dialog box. It is calculated using the auto correlation function of the matched filter signal and the decimated sampling frequency.

Gfc = the transducer gain at the center frequency, where:

fc is the center frequency (Hz)

fnominal is the nominal frequency (Hz) represented by the Frequency on the Calibration page of the Variable Properties dialog box.

G(fnominal) is calculated by looking up the value from GainTableWideband at the center frequency (Hz). When available, GainTableWideband may be viewed on the Calibration page of the Variable Properties dialog box. When GainTableWideband is unavailable, G(fnominal) 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.

ψfc = Two-way beam angle (steradian) evaluated at fc, where:

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

fc is the center frequency (Hz)

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

The Sv equation uses the linear form of two-way beam angle: Ψ = 10logψ

Notes

Sv calculations for the wideband -10 log (cτeffψfc/2) term support Soundspeed-Depth data. See also: Using sound speed profile data.

Echoview doesn't use a term for Sa correction in the Sv equation.

TSOffsetTableWideband is added to the TS equation when it is read from an ECS file or included in a data file.

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 PulseCompressedEffectivePulseDuration. 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 PulseCompressedEffectivePulseDuration.

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:

a Single target detection – wideband operator to detect single targets from pulse compressed data

a Wideband Frequency Response graph that displays the TS frequency spectrum associated with single targets

EK80 EC150-3C data

Echoview uses EK80 CW and FM equations to calculate EC150-3C Sv and TS from *.raw data. There are several unique EC150-3C handling differences:

power calculations differ from standard EK80 power

stage 1 matched filtering is different from standard EK80 matched filtering

Echoview doesn't apply a SaCorrection to Sv wideband variables

EC150-3C power calculations

where:

Pr(linear) = the received power in linear units, read from the data file, and is calculated as 10^Pr(dB)/10

irms = the RMS value of i:

where:

i is the magnitude of the real and imaginary components of the complex power read from the data file:

Real is read from the data file.

Imag is read from the data file.

Gtrd = 0.0265