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12. Glossary of Terms

    Term                       Definition                     Symbol    Units   Reference
Beamwidth                                                                cm
               Greatest distance between two points on a                       www.electropedi
   Decibel     specified axis perpendicular to the beam                  dB    a.com, 802-01-20
               axis, where the pulse-pressure-squared                    ---
 Directional   integral falls below its maximum on the                  mm     https://en.wikipe
 Response      specified axis by a specified amount.                      Ω    dia.org/wiki/Deci
  Effective                                                   w6, w10,
Hydrophone     Note – Commonly used beamwidths are                                     bel
               specified at –6 dB, –10 dB and –20 dB levels   w20                 62127-3 3.1
   Radius                                                                         62127-3 3.2
Electric Load  below the maximum. The decibel                                     62127-3 3.3
Impedance      calculation implies taking 10 times the
               logarithm (to the base 10) of the ratios of
               the integrals.

               The decibel (dB) is a logarithmic unit that    dB
               expresses the ratio of two values of a
               physical quantity. For power or intensity, it
               is calculated using the formula LP =
               10log10(P/P0) or LI = 10log10(I/I0) where
               LP is the ratio expressed in dB, P is
               measured power, P0 is reference power,
               and where LI , I, and I0 are the
               corresponding parameters for intensity.
               For pressure, it is calculated using the
               formula LF = 20log10(p/p0) where Lp is the
               ratio expressed in dB, p is the measured
               pressure, and p0 is the reference pressure.

               Description, generally presented               ---
               graphically, of the response of a
               hydrophone, as a function of direction of
               propagation of the incident plane sound
               wave, in a specified plane through the
               reference centre and at a specified
               frequency

               Radius of a stiff disc receiver hydrophone     ah,
               that has a predicted directional response      ah3,
               function with an angular width equal to the    ah6,
               observed angular width NOTE 1 The              ae,
               angular width is determined at a specified     ae3,
               level below the peak of the directional        ae6
               response function. For the specified levels
               of 3 dB and 6 dB, the radii are denoted by
               ah3 and ah6 respectively

               Complex electric input impedance               ZL
               (consisting of a real and an imaginary part)
               to which the hydrophone or hydrophone
               assembly output is connected or is to be
               connected

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