environment.propagation.outdoor_propagation

Outdoor sound propagation: ISO 9613-2:1996 general method of calculation.

This part of ISO 9613 predicts octave-band attenuation of sound propagating outdoors from a point source to a receiver under conditions favourable to propagation (moderate downwind, or the equivalent moderate temperature inversion; ISO 9613-2:1996, clause 5). The equivalent-continuous downwind octave-band sound pressure level is (ISO 9613-2:1996):

$$L_{fT}(DW)=L_W+D_{\mathrm{c}}-A\text{\hspace{1em}(Eq. 3)}$$

with $L_W$ the octave-band sound power level, $D_{\mathrm{c}}$ the directivity correction (directivity index plus a solid-angle index DOmega) and A the octave-band attenuation, itself a sum of physical mechanisms:

$$A=A_{\mathrm{div}}+A_{\mathrm{atm}}+A_{\mathrm{gr}}+A_{\mathrm{bar}}+A_{\mathrm{misc}}\text{\hspace{1em}(Eq. 4)}$$

Implemented here are the four general terms of clause 7:

• Adiv geometrical divergence, $20{\log }_{10}(d/d_0)+11$ (Eq. (7));
• Aatm atmospheric absorption, $\alpha d$ (Eq. (8)) with alpha the ISO 9613-1 coefficient supplied by air_absorption;
• Agr ground effect, both the general per-region method of 7.3.1 with the Table 3 functions a'/b'/c'/d' (Eq. (9)) and the alternative simplified method of 7.3.2 (Eq. (10));
• Abar screening by a barrier, $D_z-A_{\mathrm{gr}}$ with the Dz diffraction formula of Eq. (14) including the C2/C3 factors, the pathlength difference z (Eq. (16)/(17)), the meteorological factor Kmet (Eq. (18)) and the 20 dB (single) / 25 dB (double) limits.

The long-term average level follows from the meteorological correction Cmet (Eq. (6), (21), (22), clause 8). Amisc (foliage, industrial sites, housing; annex A) and reflections from vertical obstacles (clause 7.5) are informative and left to the caller. Accuracy of the method is stated in Table 5 (clause 9): within +/-1 dB to +/-3 dB for broadband noise up to 1000 m.

Auto-generated from the source docstrings by scripts/generate_api_docs.py (make api-docs). Do not edit by hand.

atmospheric_absorption

atmospheric_absorption(
    distance: float,
    frequencies: ArrayLike = (63.0, 125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0),
    temperature: float = 20.0,
    relative_humidity: float | None = None,
    pressure: float = 101.325,
) -> NDArray[np.float64]

Attenuation due to atmospheric absorption (ISO 9613-2:1996, Eq. (8)).

$A_{\mathrm{atm}}=\alpha d$ with alpha the ISO 9613-1 atmospheric attenuation coefficient (here in dB/m, from air_attenuation) at each octave-band midband frequency. Eq. (8) writes alpha in dB/km with $A_{\mathrm{atm}}={\alpha }_{\text{dB/km}}d/1000$; the two forms are identical.

alpha is evaluated at the exact base-10 midband frequency behind each nominal band label (e.g. 7 943.3 Hz for the “8 kHz” band), the convention behind the ISO 9613-2 Table 2 coefficients (they come from ISO 9613-1 Table 1 at exact midbands; at 8 kHz the nominal-frequency evaluation would run ~1.3 % high). Each supplied frequency is snapped to the nearest exact midband.

Parameters

Name	Description
distance	Source-to-receiver distance d, in metres.
frequencies	Octave-band midband frequencies, in hertz.
temperature	Air temperature, in degrees Celsius.
relative_humidity	Relative humidity, in percent (default 70).
pressure	Atmospheric pressure, in kilopascals.

Returns: Aatm per band, in decibels.

AtmosphericConditions

AtmosphericConditions(
    temperature: float = 20.0,
    relative_humidity: float | None = None,
    pressure: float = 101.325,
)

State of the air behind the atmospheric absorption term Aatm.

The three quantities the ISO 9613-1 attenuation coefficient alpha is a function of (ISO 9613-2:1996, Eq. (8) and Table 2). The defaults are the reference conditions of the tabulated coefficients.

Parameters

Name	Description
temperature	Air temperature, in degrees Celsius.
relative_humidity	Relative humidity, in percent; None uses 70.
pressure	Atmospheric pressure, in kilopascals.

Barrier

Barrier(
    source_to_edge: float,
    edge_to_receiver: float,
    parallel_distance: float = 0.0,
    edge_separation: float | None = None,
    ground_reflections_by_image: bool = False,
    lateral: bool = False,
    line_of_sight_clear: bool = False,
)

Screening obstacle for the ISO 9613-2 barrier term (clause 7.4).

The barrier is described by the diffraction geometry that feeds the pathlength-difference equations (16)/(17) directly, which is the cleanest match to the Dz formula of Eq. (14).

Parameters

Name	Description
source_to_edge	Distance dss from the source to the (first) diffraction edge, in metres (ISO 9613-2:1996, Eq. (16)).
edge_to_receiver	Distance dsr from the (second) diffraction edge to the receiver, in metres.
parallel_distance	Component a of the source-receiver separation parallel to the barrier edge, in metres (0 for a purely 2-D section).
edge_separation	Spacing e between the two diffraction edges for double (thick-barrier) diffraction, in metres; None selects single diffraction (Eq. (16), $C_3=1$). When given, Eq. (17) and the C3 factor of Eq. (15) are used with the 25 dB limit.
ground_reflections_by_image	When True the ground reflections are assumed to be handled separately by image sources, so $C_2=40$; otherwise $C_2=20$ (Eq. (14)).
lateral	When True the diffraction is around a vertical edge (Eq. (13)): $A_{\mathrm{bar}}=D_z$ (the ground term is not cancelled) and $K_{\mathrm{met}}=1$. Default False selects top-edge diffraction (Eq. (12)).
line_of_sight_clear	When True the line of sight between source and receiver passes above the top edge: ISO 9613-2:1996 (text after Eq. (16)) then gives the path difference z a negative sign, and Eq. (14) is still evaluated (with $K_{\mathrm{met}}=1$, Eq. (18)), so Dz falls continuously from $10{\log }_{10}3=4.8$ dB at grazing to 0 for deeper geometries. The edge distances stay the unsigned geometric lengths; only the sign convention of z changes.

Barrier.is_double

property

Whether double diffraction (Eq. (17)/(15)) applies (e given).

barrier_attenuation

barrier_attenuation(
    barrier: Barrier,
    distance: float,
    frequencies: ArrayLike = (63.0, 125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0),
) -> NDArray[np.float64]

Barrier diffraction attenuation Dz (ISO 9613-2:1996, Eq. (14)).

$$D_z=10{\log }_{10}\left[3+\frac{C_2}{\lambda }{C}_{3}z{K}_{\mathrm{met}}\right]\text{dB}$$

with $C_2=20$ (or 40 when ground reflections are handled by image sources), $C_3=1$ for single diffraction or Eq. (15) for double, the pathlength difference z (Eq. (16)/(17)), $\lambda =340/f$ and the meteorological factor Kmet (Eq. (18), 1 for $z\le 0$). Dz is limited to 20 dB (single) or 25 dB (double). When the line of sight passes above the top edge (Barrier(line_of_sight_clear=True)) z takes a negative sign (ISO 9613-2:1996, text after Eq. (16)) and Eq. (14) still applies: Dz falls continuously from $10{\log }_{10}3=4.8$ dB at grazing ($z=0$) towards 0 as the clearance deepens, clamped at 0 (the logarithm’s argument is floored at 1 — a barrier below the sight line never amplifies).

Parameters

Name	Description
barrier	Barrier geometry (Barrier).
distance	Straight-line source-to-receiver distance d, in metres.
frequencies	Octave-band midband frequencies, in hertz.

Returns: Dz per band, in decibels (>= 0).

Raises

Exception	When
ValueError	If distance or any frequency is not positive.

DEFAULT_FREQUENCIES

Constant (tuple).

DEFAULT_FREQUENCIES = (63.0, 125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0)

directivity_omega

directivity_omega(
    source_height: float,
    receiver_height: float,
    projected_distance: float,
) -> float

Solid-angle directivity index DOmega (ISO 9613-2:1996, Eq. (11)).

Accounts for the apparent increase in source power from ground reflection near the source when the alternative ground method (Eq. (10)) is used:

$$D_{\Omega }=10{\log }_{10}\left\{1+\frac{d_{\mathrm{p}}^2+(h_{\mathrm{s}}-h_{\mathrm{r}}{)}^2}{d_{\mathrm{p}}^2+(h_{\mathrm{s}}+h_{\mathrm{r}}{)}^2}\right\}\text{dB}$$

Parameters

Name	Description
source_height	Source height hs, in metres.
receiver_height	Receiver height hr, in metres.
projected_distance	Ground-plane projected distance dp, in metres.

Returns: DOmega, in decibels (0 to ~3 dB).

DirectivityCorrection

DirectivityCorrection(index: float = 0.0, d_omega: float = 0.0)

Directivity correction $D_{\mathrm{c}}=D_i+D_{\Omega }$ (Eq. (3)).

The two terms the standard adds to the sound power level of a point source: the directivity index of the source itself and the solid-angle index of the space it radiates into. Both are zero for an omnidirectional source radiating into free space.

Parameters

Name	Description
index	Source directivity index Di, in decibels.
d_omega	Solid-angle index DOmega, in decibels (see directivity_omega for the alternative ground method).

geometric_divergence

geometric_divergence(distance: float) -> float

Attenuation due to geometrical divergence (ISO 9613-2:1996, Eq. (7)).

Spherical spreading in the free field from a point source:

$$A_{\mathrm{div}}=20{\log }_{10}(d/d_0)+11\text{dB},d_0=1\text{m}$$

The +11 ($=10{\log }_{10}4\pi$) sets the sound pressure level at the reference distance $d_0=1$ m from an omnidirectional point source (Note 7).

Parameters

Name	Description
distance	Straight-line source-to-receiver distance d, in metres.

Returns: Adiv, in decibels (51 dB at 100 m, 11 dB at 1 m).

Raises

Exception	When
ValueError	If distance is not positive.

ground_attenuation

ground_attenuation(
    distance: float,
    source_height: float,
    receiver_height: float,
    frequencies: ArrayLike = (63.0, 125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0),
    ground_source: float = 0.0,
    ground_middle: float = 0.0,
    ground_receiver: float = 0.0,
    projected_distance: float | None = None,
) -> NDArray[np.float64]

Ground attenuation by the general per-region method (7.3.1, Eq. (9)).

$A_{\mathrm{gr}}=A_{\mathrm{s}}+A_{\mathrm{r}}+A_{\mathrm{m}}$ (source, receiver and middle regions), each evaluated with the Table 3 expressions and its ground factor G (0 = hard, 1 = porous, in between = porous fraction). For the source region $G=G_{\mathrm{s}}$ and $h=h_{\mathrm{s}}$; for the receiver region $G=G_{\mathrm{r}}$ and $h=h_{\mathrm{r}}$ (Table 3, note 1). The middle-region term uses the overlap factor q of note 2:

$$q=0\text{if }{d}_{\mathrm{p}}\le 30(h_{\mathrm{s}}+h_{\mathrm{r}})$$ $$q=1-\frac{30(h_{\mathrm{s}}+h_{\mathrm{r}})}{d_{\mathrm{p}}}\text{if }{d}_{\mathrm{p}}>30(h_{\mathrm{s}}+h_{\mathrm{r}})$$

with $A_{\mathrm{m}}=-3q$ at 63 Hz and $A_{\mathrm{m}}=-3q(1-G_{\mathrm{m}})$ above.

Parameters

Name	Description
distance	Straight-line source-to-receiver distance d, in metres.
source_height	Source height hs above ground, in metres.
receiver_height	Receiver height hr above ground, in metres.
frequencies	Octave-band midband frequencies, in hertz. Table 3 is defined for the eight nominal octave bands 63 Hz-8 kHz only; any other requested frequency is snapped to the nearest nominal octave band for the Table 3 lookup.
ground_source	Ground factor Gs of the source region ([0, 1]).
ground_middle	Ground factor Gm of the middle region ([0, 1]).
ground_receiver	Ground factor Gr of the receiver region ([0, 1]).
projected_distance	Ground-plane projected distance dp, in metres; defaults to $\sqrt{d^2-(h_{\mathrm{s}}-h_{\mathrm{r}}{)}^2}$.

Returns: Agr per band, in decibels (negative denotes a net gain).

Raises

Exception	When
ValueError	If a ground factor is outside [0, 1], distance is not positive, a height is negative, or a frequency is not positive.

ground_attenuation_alternative

ground_attenuation_alternative(distance: float, mean_height: float) -> float

Ground attenuation by the alternative A-weighted method (7.3.2, Eq. (10)).

Valid only when the A-weighted receiver level alone is of interest, the sound propagates over porous or mostly-porous ground and is not a pure tone (ISO 9613-2:1996, 7.3.2):

$$A_{\mathrm{gr}}=4.8-\frac{2h_{\mathrm{m}}}{d}\left[17+\frac{300}{d}\right]\ge 0\text{dB}$$

Negative results are replaced by zero. When this method is used, add the solid-angle index directivity_omega (Eq. (11)) to Dc in Eq. (3).

Parameters

Name	Description
distance	Source-to-receiver distance d, in metres.
mean_height	Mean height hm of the propagation path above the ground ($h_{\mathrm{m}}=F/d$, figure 3), in metres.

Returns: Agr, in decibels (>= 0).

Raises

Exception	When
ValueError	If distance is not positive.

GroundFactors

GroundFactors(
    source: float = 0.0,
    middle: float = 0.0,
    receiver: float = 0.0,
)

Ground factors G of the three regions (ISO 9613-2:1996, clause 7.3.1).

The general ground method splits the path into a source region, a middle region and a receiver region, each with its own factor between 0 (hard ground: paving, water, ice, compacted ground) and 1 (porous ground: grass, trees, farmland). The default is hard ground throughout.

Parameters

Name	Description
source	Ground factor Gs of the source region ([0, 1]).
middle	Ground factor Gm of the middle region ([0, 1]).
receiver	Ground factor Gr of the receiver region ([0, 1]).

meteorological_correction

meteorological_correction(
    projected_distance: float,
    source_height: float,
    receiver_height: float,
    c0: float,
) -> float

Meteorological correction Cmet (ISO 9613-2:1996, Eq. (21)/(22)).

$$C_{\mathrm{met}}=0\text{if }{d}_{\mathrm{p}}\le 10(h_{\mathrm{s}}+h_{\mathrm{r}})$$ $$C_{\mathrm{met}}=C_0\left[1-\frac{10(h_{\mathrm{s}}+h_{\mathrm{r}})}{d_{\mathrm{p}}}\right]\text{if }{d}_{\mathrm{p}}>10(h_{\mathrm{s}}+h_{\mathrm{r}})$$

C0 (dB) reflects local wind and temperature-gradient statistics; practical values lie in 0..~5 dB (note 22). Subtract Cmet from LAT(DW) for the long-term average level (Eq. (6)).

Parameters

Name	Description
projected_distance	Ground-plane projected distance dp, in metres.
source_height	Source height hs, in metres.
receiver_height	Receiver height hr, in metres.
c0	Meteorological factor C0, in decibels.

Returns: Cmet, in decibels (>= 0 for $C_0\ge 0$).

outdoor_propagation_attenuation

outdoor_propagation_attenuation(
    distance: float,
    source_height: float,
    receiver_height: float,
    frequencies: ArrayLike = (63.0, 125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0),
    ground_source: float = 0.0,
    ground_middle: float = 0.0,
    ground_receiver: float = 0.0,
    barrier: Barrier | None = None,
    temperature: float = 20.0,
    relative_humidity: float | None = None,
    pressure: float = 101.325,
    projected_distance: float | None = None,
) -> OutdoorAttenuation

Total octave-band outdoor attenuation (ISO 9613-2:1996, Eq. (4)).

Assembles the four general terms of clause 7 into $A=A_{\mathrm{div}}+A_{\mathrm{atm}}+A_{\mathrm{gr}}+A_{\mathrm{bar}}$ (the informative Amisc is omitted). The ground effect uses the general per-region method (7.3.1). With a barrier, the top-edge insertion loss $A_{\mathrm{bar}}=D_z-A_{\mathrm{gr}}$ (Eq. (12)) folds the ground effect of the screened path into Dz (note 13); for a lateral (vertical-edge) barrier $A_{\mathrm{bar}}=D_z$ (Eq. (13)) and the ground term is retained.

Parameters

Name	Description
distance	Straight-line source-to-receiver distance d, in metres.
source_height	Source height hs above ground, in metres.
receiver_height	Receiver height hr above ground, in metres.
frequencies	Octave-band midband frequencies, in hertz. The ground term snaps each frequency to the nearest nominal octave band (Table 3 is octave-band only) and the atmospheric term evaluates the exact base-10 midband behind it (see atmospheric_absorption).
ground_source	Ground factor Gs of the source region ([0, 1], 0 = hard, 1 = porous).
ground_middle	Ground factor Gm of the middle region ([0, 1]).
ground_receiver	Ground factor Gr of the receiver region ([0, 1]).
barrier	Optional screening obstacle (Barrier).
temperature	Air temperature, in degrees Celsius.
relative_humidity	Relative humidity, in percent (default 70).
pressure	Atmospheric pressure, in kilopascals.
projected_distance	Ground-plane projected distance dp, in metres; defaults to $\sqrt{d^2-(h_{\mathrm{s}}-h_{\mathrm{r}}{)}^2}$.

Returns: OutdoorAttenuation with the per-band term breakdown.

Raises

Exception	When
ValueError	If distance is not positive.

OutdoorAttenuation

OutdoorAttenuation(
    frequencies: NDArray[np.float64],
    a_div: NDArray[np.float64],
    a_atm: NDArray[np.float64],
    a_gr: NDArray[np.float64],
    a_bar: NDArray[np.float64],
    a_total: NDArray[np.float64],
    d_omega: NDArray[np.float64],
)

Per-octave-band ISO 9613-2 attenuation breakdown (clause 7).

Every array is aligned with frequencies. The terms sum, band by band, to a_total (ISO 9613-2:1996, Eq. (4) without the informative Amisc), so users can see the divergence, atmospheric, ground and barrier contributions separately.

Attributes

Name	Description
frequencies	Nominal octave-band midband frequencies, in hertz.
a_div	Geometrical divergence Adiv (Eq. (7)), in dB, per band (identical across bands).
a_atm	Atmospheric absorption Aatm (Eq. (8)), in dB, per band.
a_gr	Ground effect Agr (Eq. (9) or (10)), in dB, per band. A negative value denotes a net gain from ground reflection.
a_bar	Screening Abar (Eq. (12)/(13)), in dB, per band (>= 0).
a_total	Total attenuation A (Eq. (4)), in dB, per band.
d_omega	Solid-angle directivity index DOmega (Eq. (11)), in dB; non-zero only for the alternative ground method of 7.3.2.

OutdoorAttenuation.plot()

OutdoorAttenuation.plot(
    ax: Axes | None = None,
    *,
    language: str = 'en',
    **kwargs: Any,
) -> Axes

Plot the stacked per-band attenuation terms with the total.

Requires matplotlib (pip install phonometry[plot]); returns the Axes.

OutdoorAttenuation.report()

OutdoorAttenuation.report(
    path: str,
    *,
    metadata: ReportMetadata | None = None,
    engine: str = 'reportlab',
    verbose: bool = False,
    language: str = 'en',
    source_emission: SourceEmission | None = None,
) -> str

Render a one-page ISO 9613-2 outdoor-propagation prediction fiche.

Writes a prediction sheet (clearly labelled a prediction, not a measurement) laid out like an environmental-noise propagation calculation: the standard-basis line naming ISO 9613-2:1996 (general method, conditions favourable to propagation), an optional metadata header (source/situation, client, receiver position, meteorological conditions, date), a per-band table of the attenuation terms (Adiv, Aatm, Agr, Abar and the total A) and the attenuation-breakdown plot, closed by a boxed single result and a footer identity/disclaimer block.

When a source_emission is supplied, the fiche also lists the source power level Lw and the composed downwind level LfT(DW) per band and boxes the A-weighted downwind level LAT(DW) at the receiver, with an optional PASS/FAIL verdict against a declared limit level (a lower level is better). Without it the fiche boxes the octave-band range of the total attenuation A.

Parameters

Name	Description
path	Destination path of the PDF file.
metadata	Optional ReportMetadata supplying the header identity (specimen the source/situation, client, test_room the receiver position), the temperature / relative_humidity / pressure conditions and the footer identity. A supplied requirement is read as the maximum acceptable A-weighted downwind level in dB (used only when a source_emission is given).
engine	Rendering back end; only "reportlab" is supported.
verbose	When True and a source_emission is supplied, the per-band table adds the A-weighted band level (LfT(DW) plus the band A-weighting), whose energy sum is the boxed LAT(DW).
language	Fiche language: "en" (default) or "es".
source_emission	Optional SourceEmission (the source sound power Lw and directivity, plus an optional meteorological correction) that turns the attenuation breakdown into the boxed A-weighted downwind level at the receiver.

Returns: The written path as a str.

Raises

Exception	When
ValueError	If engine is not "reportlab", language is unknown, or a supplied source_emission sound power does not match the number of frequency bands.
ImportError	If reportlab or matplotlib is not installed (pip install "phonometry[report,plot]").

predicted_receiver_level

predicted_receiver_level(
    sound_power_level: ArrayLike,
    geometry: PropagationGeometry,
    *,
    frequencies: ArrayLike = (63.0, 125.0, 250.0, 500.0, 1000.0, 2000.0, 4000.0, 8000.0),
    ground: GroundFactors | None = None,
    barrier: Barrier | None = None,
    atmosphere: AtmosphericConditions | None = None,
    directivity: DirectivityCorrection | None = None,
    c0: float | None = None,
) -> NDArray[np.float64]

Predicted octave-band receiver level (ISO 9613-2:1996, Eq. (3)/(6)).

Composes the downwind octave-band sound pressure level:

$$L_{fT}(DW)=L_W+D_{\mathrm{c}}-A,D_{\mathrm{c}}=D_i+D_{\Omega }$$

from the total attenuation outdoor_propagation_attenuation. When c0 is given, the meteorological correction Cmet (Eq. (21)/(22)) is subtracted band by band to approximate the long-term average level LfT(LT) (Eq. (6)); the standard applies Cmet to the A-weighted level, so this is a per-band convenience.

Parameters

Name	Description
sound_power_level	Octave-band sound power level Lw, in decibels (re 1 pW), one value per frequency.
geometry	Source-to-receiver geometry of the path (PropagationGeometry): the distance d, the two heights and the optional projected distance dp.
frequencies	Octave-band midband frequencies, in hertz.
ground	Ground factors of the three regions (GroundFactors); None is hard ground throughout.
barrier	Optional screening obstacle (Barrier).
atmosphere	Air temperature, humidity and pressure behind the atmospheric absorption term (AtmosphericConditions); None is the reference air of the tabulated coefficients.
directivity	Directivity correction Dc = Di + DOmega (DirectivityCorrection); None is an omnidirectional source in free space ($D_{\mathrm{c}}=0$).
c0	Meteorological factor C0, in decibels; None returns the downwind level LfT(DW) ($C_{\mathrm{met}}=0$).

Returns: Predicted octave-band level per frequency, in decibels.

PropagationGeometry

PropagationGeometry(
    distance: float,
    source_height: float,
    receiver_height: float,
    projected_distance: float | None = None,
)

Source-to-receiver geometry of the propagation path (ISO 9613-2:1996).

The three lengths every term of the method needs: the straight-line distance d of the divergence and atmospheric terms (Eq. (7)/(8)), and the two heights above the ground the ground effect of clause 7.3.1 and the meteorological correction of clause 8 are written in.

Parameters

Name	Description
distance	Straight-line source-to-receiver distance d, in metres.
source_height	Source height hs above ground, in metres.
receiver_height	Receiver height hr above ground, in metres.
projected_distance	Ground-plane projected distance dp, in metres; None defaults to $\sqrt{d^2-(h_{\mathrm{s}}-h_{\mathrm{r}}{)}^2}$.

SourceEmission

SourceEmission(
    sound_power_level: ArrayLike,
    directivity_index: float = 0.0,
    d_omega: float = 0.0,
    cmet: float | None = None,
)

Source emission terms for the ISO 9613-2 downwind receiver level (Eq. (3)).

Passed to OutdoorAttenuation.report so the prediction fiche can box the A-weighted downwind level at the receiver from an octave-band attenuation breakdown. The level is composed as $L_{fT}(DW)=L_W+D_{\mathrm{c}}-A$ with the directivity correction $D_{\mathrm{c}}=D_i+D_{\Omega }$ (ISO 9613-2:1996, Eq. (3)); an optional meteorological correction cmet is subtracted for the long-term average level (Eq. (6)).

This report-time object keeps the emission out of outdoor_propagation_attenuation (which stays purely an attenuation calculation), so the receiver level is a presentation concern of the fiche.

Parameters

Name	Description
sound_power_level	Octave-band source sound power level Lw (dB re 1 pW), one value per band of the attenuation result.
directivity_index	Source directivity index Di, in decibels.
d_omega	Solid-angle index DOmega, in decibels (see directivity_omega for the alternative ground method).
cmet	Optional meteorological correction Cmet (dB), obtained from meteorological_correction; None reports the downwind level LfT(DW) directly ($C_{\mathrm{met}}=0$).