Environment and transport
Environmental noise is a source-path-receiver problem stretched over hundreds of metres of open air. This section covers all three of them. The propagation pages handle the path: ISO 9613 predicts, band by band, how much level survives divergence, air absorption, the ground and any barrier on the way to a receiver, and the wave-acoustic ground and refraction models say when that engineering method stops being enough.
The assessment pages handle what happens once the sound has arrived: the ISO 1996 rating level and the day-evening-night indicators, their Spanish application in RD 1367/2007, and the NT ACOU 112 adjustment that quantifies when impulsive character makes a received sound more annoying than its LAeq suggests.
The source pages handle the other end: what emits, described the way an environmental model wants it. CNOSSOS-EU gives road traffic and railways a source power per band and per category, and IEC 61400-11 rates a wind turbine by its apparent sound power and its tonal audibility. What unites them is the pattern: a carefully standardised source descriptor that the path model above then attenuates.
This section leans on the core toolkit, but only up to the period level. Integrated and Statistical Levels supplies the LAeq, percentile and event levels of each reference period; what turns those period levels into Lden, Ldn and the rating level, with the tonal adjustment, the residual-noise correction and the uncertainty budget on top, is Environmental Levels (ISO 1996-1/-2), in this section. The atmospheric absorption that every propagation model consumes is shared with the room and materials pages. Start with Outdoor Sound Propagation; it introduces the source-path-receiver bookkeeping the transport pages reuse.
The three jobs this section is normally used for combine the subsections differently. A strategic noise map is a CNOSSOS source model, a propagation model and Lden. A plant or permit assessment is a measured sound power (determined in Sources and devices), ISO 9613-2 to the nearest dwelling, and the ISO 1996 rating level with its adjustments. An activity inspection is a sound level meter at a receiver point and RD 1367/2007, or whichever national regulation applies, with no propagation model in the chain at all.
What the received sound is rated against, once it has arrived.
- Environmental Levels (ISO 1996-1/-2): the day-evening-night indicators, the rating level and the adjustments that turn a measured LAeq into an assessed one.
- Spanish Noise Regulation (RD 1367/2007): the national application of that chain, with its own limits and its own tonal, low-frequency and impulsive corrections.
- Impulsive-sound prominence (NT ACOU 112): the predicted prominence of impulsive sounds and the graduated adjustment added to LAeq.
The path from an outdoor source to a receiver, and the character of what arrives.
- Outdoor Sound Propagation: atmospheric absorption (ISO 9613-1) and the ISO 9613-2 general method with its per-term attenuation breakdown, including the tabulated ground term and the barrier screening term.
- Spherical ground effect and advanced barriers: the wave acoustics underneath those two fits — the Weyl-Van der Pol spherical-wave reflection coefficient over finite-impedance ground, and wave-theoretic screen diffraction.
- Atmospheric refraction: how wind and temperature gradients bend a ray into or out of a shadow zone.
What emits, described the way an environmental model wants it: a source strength per band, ready for the path above to attenuate.
- CNOSSOS-EU road traffic source emission: the rolling and propulsion power of a traffic stream, per vehicle category and per band.
- CNOSSOS-EU railway source emission: the equivalent for rail, with its source heights and its rolling, traction and aerodynamic contributions.
- Wind-turbine noise: sound power and tonal audibility: the IEC 61400-11 apparent sound power level and tonal-audibility chain.
Aircraft are the other transport source with internationally fixed metrics, and they have a topic of their own: Aircraft noise.
What this section does not cover
Section titled “What this section does not cover”Only the source side of CNOSSOS-EU Annex II is implemented, and only two of its four sources. The industrial source of section 2.4 and Appendix H, and the aircraft source of sections 2.6 and 2.7, are not implemented; aircraft noise is covered by the ICAO and ECAC methods in Aircraft noise, which is a different family of models, and a non-vehicle machine is characterised as a sound power in Sources and devices. The CNOSSOS propagation method of section 2.5 is not implemented either: the path here is ISO 9613-2, a different model, so a chain built from CNOSSOS sources and this library’s propagation is not a CNOSSOS calculation and should not be reported as one.
Nothing here is a mapping engine. There is no terrain model, no city geometry and no GIS layer: the propagation functions take one source, one receiver and the ground between them, both refraction models assume flat ground at z = 0, and how a source line is split into point sources is declared out of scope by CNOSSOS itself. On the assessment side, the library starts where the sound level meter stops — the ISO 1996-2 receiver positions and façade corrections, and the RD 1367/2007 Annex IV measurement procedures (microphone positions, series duration, number of measurements), are not implemented, only the arithmetic that follows once you have applied them. Acoustic zoning, noise maps and action plans under Ley 37/2003 are planning instruments, not calculations.
Before and after these pages
Section titled “Before and after these pages”Every rating here is an adjusted , so the calibration, weighting and time integration that produce it are in Signal analysis, and Build a sound level meter runs that chain end to end on one runnable page. The derivations are in Environment and transport theory: the ISO 1996-1 descriptors, the NT ACOU 112 prominence criterion and the ISO 9613 attenuation terms.
If you arrived here from a search and want the shape of the whole library, What do you need to measure? indexes it by the job and All guides lists every page with a line on each.