compute_TS

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compute_TS#

echopype.calibrate.compute_TS(echodata: EchoData, **kwargs)#

Compute target strength (TS) from raw data.

The calibration routine varies depending on the sonar type. Currently this operation is supported for the following sonar_model: EK60, AZFP, EK80 (see Notes below for detail).

Parameters
echodataEchoData

An EchoData object created by using open_raw or open_converted

env_paramsdict, optional

Environmental parameters needed for calibration. Users can supply “sound speed” and “absorption” directly, or specify other variables that can be used to compute them, including “temperature”, “salinity”, and “pressure”.

For EK60 and EK80 echosounders, by default echopype uses environmental variables stored in the data files. For AZFP echosounder, all environmental parameters need to be supplied. AZFP echosounders typically are equipped with an internal temperature sensor, and some are equipped with a pressure sensor, but automatically using these pressure data is not currently supported.

cal_paramsdict, optional

Intrument-dependent calibration parameters.

For EK60, EK80, and AZFP echosounders, by default echopype uses environmental variables stored in the data files. Users can optionally pass in custom values shown below.

  • for EK60 echosounder, allowed parameters include: “sa_correction”, “gain_correction”, “equivalent_beam_angle”

  • for AZFP echosounder, allowed parameters include: “EL”, “DS”, “TVR”, “VTX0”, “equivalent_beam_angle”, “Sv_offset”

Passing in calibration parameters for other echosounders are not currently supported.

waveform_mode{“CW”, “BB”, “FM”}, optional

Type of transmit waveform. Required only for data from the EK80 echosounder and not used with any other echosounder.

  • “CW” for narrowband transmission, returned echoes recorded either as complex or power/angle samples

  • “BB” or “FM” for broadband transmission, returned echoes recorded as complex samples

encode_mode{“complex”, “power”}, optional

Type of encoded return echo data. Required only for data from the EK80 echosounder and not used with any other echosounder.

  • “complex” for complex samples

  • “power” for power/angle samples, only allowed when the echosounder is configured for narrowband transmission

Returns
xr.Dataset

The calibrated TS dataset, including calibration parameters and environmental variables used in the calibration operations.

Notes

The EK80 echosounder can be configured to transmit either broadband/frequency modulated (waveform_mode="BB" or waveform_mode="FM") or narrowband (waveform_mode="CW") signals. When transmitting in broadband mode, the returned echoes are encoded as complex samples (encode_mode="complex"). When transmitting in narrowband mode, the returned echoes can be encoded either as complex samples (encode_mode="complex") or as power/angle combinations (encode_mode="power") in a format similar to those recorded by EK60 echosounders.

The current calibration implemented for EK80 broadband complex data uses band-integrated TS with the gain computed at the center frequency of the transmit signal.

Note that in the fisheries acoustics context, it is customary to associate TS to a single scatterer. TS is defined as: TS = 10 * np.log10 (sigma_bs), where sigma_bs is the backscattering cross-section.

For details, see: MacLennan et al. 2002. A consistent approach to definitions and symbols in fisheries acoustics. ICES J. Mar. Sci. 59: 365-369. https://doi.org/10.1006/jmsc.2001.1158

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