Calibration settings for HAC data

For details on your specific data, please refer to the following pages:

Calibration notes

When you create a HAC data file from one of your original echograms, it writes the Sv sample values from that echogram into the file; if your original echogram is already ‘calibrated’ (i.e. showing the correct time, location and Sv for each sample), then your HAC file is also calibrated and no changes are necessary. Note also that ‘no data’ values (if you have any) are not translated from your original echogram into your HAC echogram. ‘No data’ values above the surface exclusion line are converted to -999 dB, while ‘no data’ samples below the bottom exclusion line are removed completely.

It is possible (but not advisable) to change supported calibration parameters for a HAC file in order to recalculate the sample Sv values in Echoview. See listed notes below.

It is advised that if you do need to change one or more of the calibration parameters (e.g. absorption coefficient), you can change it for the original data and then recreate the HAC file.

HAC data files contain Sv as the ‘raw’ sample value; this is different from RAW data files, which contain Pr (received power) as the ‘raw’ sample value from which Sv can be calculated.
Sv is calculated as a function of received power, TVG and a number of ‘calibration’ parameters such as absorption coefficient, gain and sound speed. For more information refer to EK60_Power_to_Sv_and_TS.htm.
However, Echoview still needs to know the calibration parameters for your HAC data (via an ECS file) because Sv is not the only value that requires calibration parameters; for example, TwoWayBeamAngle is required in order to calculate Beam_volume_sum (see Additional uses of calibration settings).
CalibrationOffset is a generic offset parameter provided for non-native data formats such as HAC and EK5; it tells Echoview how many decibels to add or subtract from each sample, which is why you can leave it set to 0 for your HAC data (which should already be calibrated).
You can adjust sound speed in your HAC data by using SoundSpeed and SoundSpeedLogging in an ECS file; it works by providing the original sound speed so that you can back-calculate and then apply the new sound speed.
You do not need to use either SoundSpeed or SoundSpeedLogging if the sound speed was correctly applied to your original data that the HAC files were exported from. If you do include a SoundSpeed value in your ECS file you should also include SoundSpeedLogging (or vice versa), otherwise 1500 will be used as a default for the one that is missing and data will be incorrectly adjusted. Applied TVG for Sv and TS is affected by these changes. New TVG is applied under the assumption that TVG was applied to Sv and TS data.

You can adjust the absorption coefficient in your HAC data by using AbsorptionCoefficient and AbsorptionCoefficientLogging in an ECS file; it works by providing the original absorption coefficient so that you can back-calculate and then apply the new absorption coefficient.
You do not need to use either AbsorptionCoefficient and AbsorptionCoefficientLogging if the absorption coefficient was correctly applied to your original data that the HAC files were exported from. If you do include an AbsorptionCoefficient in your ECS file you should also include AbsorptionCoefficientLogging (or vice versa), otherwise 0.100 will be used as a default for the one that is missing and data will be incorrectly adjusted. Applied TVG for Sv and TS is affected by these changes. New TVG is applied under the assumption that TVG was applied to Sv and TS data.

Calibration settings for HAC data

Calibration notes

See also