MB-System Unix Manual Page: mbabsorption

### MB-System Unix Manual Page

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    mblevitus
    Section:  MB-System 5.0  (1)
    Updated:  26 October 2009
    Index

    NAME

    mbabsorption - calculates the absorption of sound in sea water in dB/km
    as a function of frequency, temperature, salinity, sound speed, and depth.

    VERSION

    Version 5.0

    SYNOPSIS

    mbabsorption [-Csoundspeed -Ddepth
    -Ffrequency -Pph -Ssalinity -Ttemperature -V -H]

    DESCRIPTION

    mbabsorption - calculates the absorption of sound in sea water in dB/km

     as a function of frequency (kHz), temperature (degrees C), salinity (per mil),
    depth (m), pH, and water sound speed (m/sec).

     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

    Parameters:

            f = sound frequency (kHz)

            c = speed of sound (m/s)

            T = temperature (deg C)

            Tk = temperature (deg K) = T + 273 (deg K)

            S = salinity (per mil)

            D = depth (m)

    If the speed of sound is not specified by the user, it will be
    calculated from temperature, salinity, and depth using:

            c =~ 1412 + 3.21 * T + 1.19 * S + 0.0167 * D

    Normally, mbabsorption simply prints the resulting absorption
    value to stdout. If the -V option is specified, the output will
    include a listing of the parameters used in calculating the absorption.

    AUTHORSHIP

    David W. Caress (caress@mbari.org)

      Monterey Bay Aquarium Research Institute

    Dale N. Chayes (dale@ldeo.columbia.edu)

      Lamont-Doherty Earth Observatory

    OPTIONS

    -H

    This "help" flag cause the program to print out a description
    of its operation and then exit immediately.
    -C

    soundspeed

    Specifies the water sound speed in m/sec. If the option is
    not used, the water sound speed will be calculated from the
    temperature, salinity, and depth.
    -D

    depth

    Sets the depth in meters at which the sound absorption should be calculated.
    Default: depth = 0.0 m (i.e. the sea surface).
    -F

    frequency

    Sets the sound frequency in kHz at which the sound absorption should be calculated.
    Default: frequency = 200 kHz.
    -P

    ph

    Sets the pH value at which the sound absorption should be calculated.
    Default: ph = 8.
    -S

    salinity

    Sets the salinity in per mil at which the sound absorption should be calculated.
    Default: salinity = 35 per mil.
    -T

    temperature

    Sets the temperature in degrees C at which the sound absorption should be calculated.
    Default: temperature = 10.0 degrees C.
    -V

    Normally, mbabsorption outputs only a single absorption value
    to the stdout stream.  If the
    -V flag is given, then mbabsorption works in a "verbose" mode and
    also outputs the parameters used to calculate the absorption.

    EXAMPLES

    Suppose that one wishes to obtain the water sound absorption for
    a 200 kHz multibeam sonar operating at a depth of 1000 meters (on
    an AUV, for instance) in water with a salinity of 35 per mil, a pH
    of 8, and a temperature of 4 degrees C. The following will suffice:

            mbabsorption -D1000 -F200 -P8 -S35 -T4

    The output will be:

     37.692561

    In order to obtain a more readable result, use the -V option:

            mbabsorption -D1000 -F200 -P8 -S35 -T4 -V

    The output will be:

     Program MBabsorption

     Version $Id: mbabsorption.1 1783 2009-10-26 23:33:35Z caress $

     MB-system Version 5.1.1beta15

     Input Parameters:

          Frequency:        200.000000 kHz

          Temperature:      4.000000 deg C

          Salinity:         35.000000 per mil

          Depth:            1000.000000 m

          pH:               8.000000

     Result:

          Sound absorption: 37.692561 dB/km

    SEE ALSO

    mbsystem(l)

    BUGS

    None known.

     Index

    NAME
    VERSION
    SYNOPSIS
    DESCRIPTION
    AUTHORSHIP
    OPTIONS
    EXAMPLES
    SEE ALSO
    BUGS

Last Updated: 26 October 2009

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