/*-------------------------------------------------------------------- * The MB-system: mb_absorption.c 2/10/2008 * $Id: mb_absorption.c 1917 2012-01-10 19:25:33Z caress $ * * Copyright (c) 2008-2012 by * David W. Caress (caress@mbari.org) * Monterey Bay Aquarium Research Institute * Moss Landing, CA 95039 * and Dale N. Chayes (dale@ldeo.columbia.edu) * Lamont-Doherty Earth Observatory * Palisades, NY 10964 * * See README file for copying and redistribution conditions. *--------------------------------------------------------------------*/ /* * mb_absorption.c includes a "mb_" function used to calculate * the absorption of sound in sea water in dB/km as a * function of frequency, temperature, salinity, and pressure. * * We use the Francois and Garrison equations from: * Francois, R.E., Garrison, G.R., "Sound absorption based * on ocean measurements: Part I: Pure water and magnesium * sulfate contributions", J. Acoust. Soc. Am., 72(3), * 896-907, 1982. * Francois, R.E., Garrison, G.R., "Sound absorption based * on ocean measurements: Part II: Boric acid contribution * and equation for total absorption", J. Acoust. Soc. Am., * 72(6), 1879-1890, 1982. * * Francois and Garrison [1982] model the sound absorption in * sea water as resulting from contributions from pure water, * magnesium sulfate, and boric acid. The boric acid contribution * is significant below 10 kHz. The equations are: * * absorption = Boric Acid Contribution * + MbSO4 Contribution * + Pure Water Contribution * * ************************** * * Boric Acid Contribution * AlphaB = Ab * Pb * Fb * f**2 * ------------------- * f**2 + Fb**2 * * Ab = 8.86 / c * 10**(0.78 * pH - 5) (dB/km/kHz) * Pb = 1 * Fb = 2.8 * (S / 35)**0.5 * 10**(4 - 1245 / Tk) (kHz) * * ************************** * * MgSO4 Contribution * AlphaM = Am * Pm * Fm * f**2 * ------------------- * f**2 + Fm**2 * * Am = 21.44 * S * (1 + 0.025 * T) / c (dB/km/kHZ) * Pm = 1 - 0.000137 * D + 0.0000000062 * D**2 * Fm = (8.17 * 10**(8 - 1990 / Tk)) / (1 + 0.0018 * (S - 35)) (kHz) * * ************************** * * Pure Water Contribution * AlphaW = Aw * Pw * f**2 * * For T <= 20 deg C * Aw = 0.0004397 - 0.0000259 * T * + 0.000000911 * T**2 - 0.000000015 * T**3 (dB/km/kHz) * For T > 20 deg C * Aw = 0.0003964 - 0.00001146 * T * + 0.000000145 * T**2 - 0.00000000049 * T**3 (dB/km/kHz) * Pw = 1 - 0.0000383 * D + 0.00000000049 * D**2 * * ************************** * * c = speed of sound (m/s) * =~ 1412 + 3.21 * T + 1.19 * S + 0.0167 * D * T = temperature (deg C) * Tk = temperature (deg K) = T + 273 (deg K) * S = salinity (per mil) * D = depth (m) * * ************************** * * Author: D. W. Caress * Date: February 10, 2008 * R/V Zephyr * Hanging out at the channel entrance to La Paz, BCS, MX * helping out as MBARI tries to save the grounded * R/V Western Flyer. * Note: as I was writing this code the Flyer was refloated * and successfully backed off the reef. * * $Log: mb_absorption.c,v $ * Revision 5.0 2008/03/01 09:19:29 caress * Added function to calculate sound absoprtion in water from water properties parameters. * * */ /* standard include files */ #include #include /* mbio include files */ #include "../../include/mb_status.h" #include "../../include/mb_define.h" /*--------------------------------------------------------------------*/ int mb_absorption(int verbose, double frequency, double temperature,double salinity, double depth, double ph, double soundspeed, double *absorption, int *error) { char *function_name = "mb_absorption"; int status = MB_SUCCESS; double Alphab, Alpham, Alphaw; double tk; double Ab, Pb, Fb; double Am, Pm, Fm; double Aw, Pw; /* print input debug statements */ if (verbose >= 2) { fprintf(stderr,"\ndbg2 MBIO function <%s> called\n", function_name); fprintf(stderr,"dbg2 Input arguments:\n"); fprintf(stderr,"dbg2 verbose: %d\n",verbose); fprintf(stderr,"dbg2 frequency: %f\n",frequency); fprintf(stderr,"dbg2 temperature:%f\n",temperature); fprintf(stderr,"dbg2 salinity: %f\n",salinity); fprintf(stderr,"dbg2 soundspeed: %f\n",soundspeed); fprintf(stderr,"dbg2 depth: %f\n",depth); fprintf(stderr,"dbg2 ph: %f\n",ph); } /* calculate sound speed if needed */ if (soundspeed <= 0.0) soundspeed = 1412.0 + 3.21 * temperature + 1.19 * salinity + 0.0167 * depth; /* get temperature in deg Kelvin - I know the conversion is slightly wrong, but this is what they published.... */ tk = temperature + 273.0; /* calculate boric acid contribution */ Ab = 8.86 / soundspeed * pow(10.0, (0.78 * ph - 5.0)); Pb = 1.0; Fb = 2.8 * sqrt(salinity / 35.0) * pow(10.0, (4.0 - (1245.0 / tk))); Alphab = (Ab * Pb * Fb * frequency * frequency) / (Fb * Fb + frequency * frequency); /* calculate MgSO4 contribution */ Am = 21.44 * salinity * (1 + 0.025 * temperature) / soundspeed; Pm = 1 - 0.000137 * depth + 0.0000000062 * depth * depth; Fm = (8.17 * pow(10.0, (8.0 - 1990.0 / tk))) / (1 + 0.0018 * (salinity - 35)); Alpham = (Am * Pm * Fm * frequency * frequency) / (Fm * Fm + frequency * frequency); /* calculate pure water contribution */ if (temperature <= 20.0) Aw = 0.0004397 - 0.0000259 * temperature + 0.000000911 * temperature * temperature - 0.000000015 * temperature * temperature * temperature; else Aw = 0.0003964 - 0.00001146 * temperature + 0.000000145 * temperature * temperature - 0.00000000049 * temperature * temperature * temperature; Pw = 1 - 0.0000383 * depth + 0.00000000049 * depth * depth; Alphaw = Aw * Pw * frequency * frequency; /* add it all together */ *absorption = Alphab + Alpham + Alphaw; /* assume success */ *error = MB_ERROR_NO_ERROR; status = MB_SUCCESS; /* print output debug statements */ if (verbose >= 2) { fprintf(stderr,"\ndbg2 MBIO function <%s> completed\n", function_name); fprintf(stderr,"dbg2 Return values:\n"); fprintf(stderr,"dbg2 absorption: %f\n",*absorption); fprintf(stderr,"dbg2 error: %d\n",*error); fprintf(stderr,"dbg2 Return status:\n"); fprintf(stderr,"dbg2 status: %d\n",status); } /* return status */ return(status); }