Source: https://jmrplens.github.io/phonometry/guides/sections/environment-transport/ Environmental noise is a source-path-receiver problem stretched over hundreds of metres of open air. This section covers both ends of it. The **outdoor sound** pages handle the path and the assessment: 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 NT ACOU 112 quantifies when impulsive character makes the received sound more annoying than its LAeq suggests. The **aircraft and wind energy** pages handle transport sources that come with their own internationally fixed metrics. Aircraft noise certification runs on the Effective Perceived Noise Level of ICAO Annex 16, with the airport-contour machinery of ECAC Doc 29 built on top; helicopters get the directional noise-hemisphere source model of ECAC Doc 32; and wind turbines are rated by the apparent sound power and tonal audibility of IEC 61400-11. What unites them is the pattern: a carefully standardised source descriptor plus standardised propagation adjustments. This section leans on the core toolkit more than any other: the rating levels and Lden that environmental assessment ends in live in [Integrated and Statistical Levels](/phonometry/guides/levels/), and the atmospheric absorption that every propagation model consumes is shared with the room and materials pages. Start with [Outdoor Sound Propagation](/phonometry/guides/outdoor-propagation/); it introduces the source-path-receiver bookkeeping the transport pages reuse. ## [Outdoor sound](/phonometry/guides/sections/outdoor-sound/) The path from an outdoor source to a receiver, and the character of what arrives. - [Outdoor Sound Propagation](/phonometry/guides/outdoor-propagation/): atmospheric absorption (ISO 9613-1) and the ISO 9613-2 general method with its per-term attenuation breakdown. - [Impulsive-sound prominence (NT ACOU 112)](/phonometry/guides/impulse-prominence/): the predicted prominence of impulsive sounds and the graduated adjustment added to LAeq. ## [Aircraft and wind energy](/phonometry/guides/sections/aircraft-wind/) Transport and energy sources with their own certification metrics. - [Aircraft noise: Effective Perceived Noise Level](/phonometry/guides/aircraft-noise/): the ICAO Annex 16 EPNL, the IEC 61265 measurement-system verifier, SAE ARP 5534 atmospheric absorption and ECAC Doc 29 NPD interpolation. - [Rotorcraft noise: the hemisphere method](/phonometry/guides/rotorcraft-noise/): the ECAC Doc 32 noise-hemisphere source model with its propagation adjustments. - [Wind-turbine noise: sound power and tonal audibility](/phonometry/guides/wind-turbine-noise/): the IEC 61400-11 apparent sound power level and tonal-audibility chain.