calc_absorption

echopype.utils.uwa.calc_absorption(frequency, temperature=27, salinity=35, pressure=10, pH=8.1, sound_speed=None, formula_source='AM')

Calculate sea water absorption in units [dB/m].

Parameters

frequency: int or numpy array

frequency [Hz]

temperature: num

temperature [deg C]

salinity: num

salinity [PSU, part per thousand]

pressure: num

pressure [dbars]

pH: num

pH of water

formula_source: str, {“AM”, “FG”, “AZFP”}

Source of formula used to calculate sound speed. “AM” (default) uses the formula from Ainslie and McColm (1998). “FG” uses the formula from Francois and Garrison (1982). “AZFP” uses the the formula supplied in the AZFP Matlab code. See Notes below for the references.

Returns

Sea water absorption [dB/m].

Notes

Ainslie MA, McColm JG. (1998). A simplified formula for viscous and chemical absorption in sea water. The Journal of the Acoustical Society of America, 103(3), 1671–1672. https://doi.org/10.1121/1.421258

Francois RE, Garrison GR. (1982). Sound absorption based on ocean measurements. Part II: Boric acid contribution and equation for total absorption. The Journal of the Acoustical Society of America, 72(6), 1879–1890. https://doi.org/10.1121/1.388673

The accuracy of the simplified formula from Ainslie & McColm 1998 compared with the original complicated formula from Francois & Garrison 1982 was demonstrated between 100 Hz and 1 MHz.