|Description / Abstract
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|This part of ANSI/ASA S12.64 describes the general measurement
systems, procedures, and methodologies used for the measurement of
underwater sound pressure levels from ships at a prescribed
operating condition. It contains methodology for the reporting of
one-third octave band sound pressure levels. The resulting
quantities are the sound pressure levels normalized to a distance
of 1 m. Since the underwater sound pressure levels are affected by
the presence of the free surface (and sometimes the bottom), such
quantities are considered "affected source levels," herein referred
to as source levels.
The underwater sound pressure level measurements are performed
in the geometric far field and then adjusted to the 1 m normalized
distance for use in comparison with appropriate underwater noise
criteria. However, this standard does not specify or provide
guidance on underwater noise criteria or address the potential
effects of noise on marine organisms. This standard is applicable
to any and all underway surface vessels, either manned or unmanned.
The methods have no inherent limitation on minimum or maximum
This standard is not applicable to submerged vessels or to
aircraft. This standard is limited to vessels transiting at speeds
no greater than 50 knots (25.70 m/s). The measurement methods
mitigate the variability caused by Lloyd's Mirror surface image
coherence effects (see 3.16), but do not exclude a possible
influence of bottom reflections. No specific computational
adjustments for either of these effects are part of this standard.
A specific ocean location is not required to use this standard, but
the requirements for an ocean test site are provided.
The intended uses of the methods described in this standard are:
to show compliance with contract requirements, to enable periodic
signature assessments, and for research and development. The
intended users include: government agencies, research vessel
operators, and commercial vessel owners that need to operate in
acoustically sensitive waters.
This standard offers three grades of measurement, each with a
stated applicability, test methodology, uncertainty, system
repeatability, and complexity. A summary of the attributes of each
"Grade" (denoted A, B, and C) is given in Table 1.
|Additional Supplemental Documents