There are several tools for analyzing jet aircraft sound as measured on the ground. The measurements would typically be made for takeoff and final approach at or near an airport. Fly-over sound levels can also be recorded.
The tools begin with the unweighted, one-third octave sound pressure level (SPL). One SPL should be taken for each 0.5 second increment. Furthermore, each SPL should have an overall sound pressure level that is within 10 dB of the maximum overall level.
The tools build upon one another in this order:
- Sound Pressure Level (SPL)
- Perceived Noisiness (Noys)
- Perceived Noise Level (PNL)
- Tone Corrected Perceived Noise Level (PNLT)
- Effective Perceived Noise Level (EPNL)
Each of the functions is in units of dB except for Noys. The Effective Perceived Noise Level is sometimes represented as EPNdB to emphasize that it is a decibel scale. The functions are defined in Annex 16 of the ICAO International Convention on Civil Aviation, and in the US Federal Air Regulations Part 36.
Noy is a subjective unit of noisiness. A sound of 2 noys is twice as noisy as a sound of 1 noy and half as noisy as a sound of 4 noys.
The Matlab scripts for the EPNL processing are included in the GUI package at: Vibrationdata Matlab Signal Analysis Package
The function can accessed via:
>> vibrationdata > Select Input Data Domain > Sound Pressure Level
An alternative is to compute the A-weighted SPL. This option is also available in the Matlab GUI package. Nevertheless, the EPNL is used by convention for jet aircraft noise.
– Tom Irvine