Compute volume backscattering strength (Sv) 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).
An EchoData object created by using open_raw or open_converted
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.
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.
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” for broadband transmission, returned echoes recorded as complex samples
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
The calibrated Sv dataset, including calibration parameters and environmental variables used in the calibration operations.
The EK80 echosounder can be configured to transmit
either broadband (waveform_mode="BB"
)
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 Sv with the gain computed at the center frequency of the transmit signal.
The returned xr.Dataset will contain the variable water_level from the EchoData object provided, if it exists. If water_level is not returned, it must be set using EchoData.update_platform().