ISO 17208-1:2016 水中音響—船からの水中音の記述と測定の量と手順—パート1：比較目的で使用される深海での正確な測定の要件 | ページ 6

3.1

background noise

noise from all sources (biotic and abiotic) other than the ship being measured, including self noise

Note 1 to entry: See 6.2 for background noise adjustments.

[SOURCE:ISO 11202:2010, 3.17, modified – in the definition, added “(biotic and abiotic)” and changed “source under test” to “ship being measured”.]

3.2

beam aspect

direction to either side of the ship under test perpendicular to the vertical plane through the middle of the ship from front to back

Note 1 to entry: Beam aspect refers to the location of the hydrophone(s) with respect to the ship under test and is typically referred to as port or starboard directions. Another approach for hydrophone measurement (not applied here) is keel aspect where the hydrophone(s) are below the keel of the ship under test.

3.3

closest point of approach

CPA

point where the horizontal distance (during a test run) from the ship reference point of the ship under test to the hydrophone(s) is the smallest

Note 1 to entry: The distance to the hydrophone at the closest point of approach is defined by the symbol d_CPA as used in Formula (1).

3.4

commence exercise

COMEX

start test range location

position of the ship reference point of the ship under test at least twice (2x) the distance of the “start data” location ahead of the closest point of approach

Note 1 to entry: See Figure 3.

3.5

data window angle

angle subtended at the hydrophone, between the start data location and the end data location

Note 1 to entry: The data window angle is expressed as a value in degrees as shown in Figure 3.

Note 2 to entry: The data window angle is ±30°.

3.6

data window length

DWL

l_DW

distance between the start data location and end data location

Note 1 to entry: The DWL is defined by the distance at closest point of approach and the data window angle of ±30° as given in Formula (1) and shown in Figure 3.

3.7

data window period

DWP

t_DWP

time it takes the ship under test to travel the data window length at a certain speed

Note 1 to entry: See Formula (2) and Figure 3.

3.8

end data location

position of the ship reference point of the ship under test where data recording is ended

Note 1 to entry: End data location is one data window length after the start data location. See Figure 3.

3.9

field calibration

method of using known inputs, possibly using physical stimuli (such as a known, calibrated and traceable acoustic or vibration source) or electrical input (charge or voltage signal injection) at the input (or other stage) of a measurement system in order to ascertain that the system is, in fact, responding properly (i.e. within the system’s stated uncertainty) to the known stimulus

3.10

finish exercise

FINEX

end test range location

position of the ship reference point of the ship under test twice (2x) the distance to the “start data” location past the closest point of approach

Note 1 to entry: See Figure 3.

3.11

frequency response

frequency range a system is able to measure, for a given uncertainty and repeatability, from the lowest frequency to the highest stated frequency

3.12

geometric far field

horizontal distance from the ship under test at which the assumption of source co-location causes less than 1 dB difference between the actual measurement and the hypothetical result when adjusting to the reference far field distance

Note 1 to entry: The definition for acousticfar field in ISO 18405 also applies.

3.13

hydrophone cable drift angle

angle between the vertical axis and the line created between the fixed support of the hydrophone cable and the hydrophone

3.14

insert voltage calibration

known, calibrated and traceable input stimulus in the form of an electrical input injected at the input (or other stage) of a measurement system in order to ascertain that the system is, in fact, responding properly (i.e. within the system’s stated uncertainty and repeatability) to a known stimulus

3.15

Lloyd's mirror surface image coherence effects

alteration of radiated noise levels caused by the presence of a free (pressure release) surface

Note 1 to entry: Radiation from the surface image constructively and destructively influences the source's direct radiation. For this part of ISO 17208, these effects are considered as part of the source's radiation, causing it to exhibit a vertical directivity and necessitating the acquisition angle(s) is defined.

Note 2 to entry: Lloyd’s mirror effects are reduced but not removed from the final radiated noise level determined herein.

3.16

measurement repeatability

expected dispersion of radiated noise levels resulting from successive measurements on the same ship at the same operating condition, carried out under the same conditions of measurement with the same equipment at the same location

Note 1 to entry: Measurement repeatability is stated in decibels and in one-third octave bands.

3.17

measurement system

data acquisition system consisting of, but not limited to, one or more transducer(s), conditioning amplifier(s), analogue-to-digital converter(s), digital signal processing computer and ancillary peripherals

3.18

measurement uncertainty

expected dispersion of the measured radiated noise level values

Note 1 to entry: Measurement uncertainty is stated in decibels for one-third octave bands using a given measurement method (averaging time, bandwidth-time product, etc.).

Note 2 to entry: See Clause 7.

3.19

omni-directional hydrophone

underwater sound pressure transducer that responds nearly equally to sound from all directions with a variation in sensitivity with horizontal direction not exceeding ±2 dB within the frequency range of the measurements.

3.20

overall ship length

longitudinal distance between the forward-most and aft-most part of a ship

3.21

radiated noise level

RNL

L_rn

level of the product of the distance from a ship reference point of a sound source, d, and the far field root-mean-square sound pressure, p_rms(d), at that distance for a specified reference value

Note 1 to entry: LRN = 20 log₁₀ (p_rms/p₀) dB + 20 log₁₀ (d/d₀) dB.

Note 2 to entry: Radiated noise level is expressed in decibels (dB).

Note 3 to entry: The reference value for sound pressure (p₀) is 1 µPa. The reference value for distance (d₀) is 1 m. The combined RNL reference value is p₀d₀ is 1 μPa·m.

Note 4 to entry: The resulting level is denoted “LRN, dB re 1 µPa·m”. This designation replaces the past use of “Lp, dB re 1 µPa @ 1 m”.

Note 5 to entry: RNL varies in both horizontal and vertical aspect in the far field. This procedure determines an azimuthal sector averaged about the hydrophone position; and vertical-elevation averaged quantity in the beam aspect about the ship reference point.

3.22

root-mean-square sound pressure level

sound pressure level

SPL

L_p

for a specified reference value, p₀, the level of the root-mean-square sound pressure, p_rms

Note 1 to entry: In formula form, L_p = 20 log₁₀(p_rms/p₀) dB, where p_rms is the root-mean-square sound pressure.

Note 2 to entry: Root-mean-square sound pressure level is expressed in decibels (dB).

Note 3 to entry: In underwater acoustics, the reference value of root-mean-square sound pressure, p₀, is 1 μPa.

Note 4 to entry: Frequency weighting and time weighting, as applicable, shall be specified.

Note 5 to entry: Root-mean-square sound pressure is a field quantity (see ISO 80000-3:2006, Clause 3 and ISO 80000-1:2009, Annex C).

Note 6 to entry: The abbreviations “RMS SPL” and “root-mean-square SPL” are deprecated because in normal use of English, these would mean “root-mean-square value of SPL”, which means something different from “level of the root-mean-square sound pressure”.

3.23

ship reference point

point on the ship from which the distances are defined

Note 1 to entry: For the purpose of this part of ISO 17208, the ship reference point is located transversely at the ship centreline, longitudinally a quarter-length forward of the stern and vertically at the height of the sea surface.

Note 2 to entry: The location for the ship reference point applies for all frequencies.

Note 3 to entry: The ship reference point may also serve as an approximate location for the ship’s acoustic centre.

3.24

slant range

distance from the ship reference point of the ship under test to each hydrophone

3.25

sound speed profile

measure of the speed of sound in seawater as a function of depth, measured vertically through the water column

3.26

start data location

position of the ship reference point of the ship under test where data recording is started

Note 1 to entry: See Figure 3.

3.27

test site

location where the underwater noise measurements are performed