Measurement of Noise Around Airports: Standards, Methods, and Compliance Testing

Measurement of noise around airports is the systematic monitoring and evaluation of aircraft-generated sound in the vicinity of aerodromes to verify compliance with limits specified in standards such as GB 9660, GB 9661, ISO 20906, and ICAO Annex 16. Accredited third-party laboratories use Class 1 sound level meters and noise monitoring terminals to quantify key metrics including WECPNL, LAeq, Lden, and EPNL at noise-sensitive receptors. This article explains the technical basis, measurement points, testing items, methodologies, and typical applications of airport surrounding noise measurement.

Technical Overview

Airport surrounding noise measurement is an environmental acoustics service that quantifies the noise impact of aircraft operations on communities near aerodromes. Aircraft noise differs from other transportation noise because it is intermittent, highly directional, and dominated by discrete flight events with high peak levels and broadband spectral content, including strong low-frequency components from jet engines and turbofans.

Primary Noise Sources

• Takeoff and climb-out operations with high engine thrust settings
• Approach and landing, including landing gear, high-lift devices, and reverse thrust deployment
• En-route overflights in the vicinity of departure and arrival corridors
• Ground operations such as taxiing, auxiliary power units, and maintenance engine run-ups

Evaluation Metrics

The Chinese national standard GB 9660-1988, "Standard of Noise Around Airport," uses the Weighted Equivalent Continuous Perceived Noise Level (WECPNL) as the governing evaluation index. WECPNL is derived from the Effective Perceived Noise Level (EPNL) of individual flight events, averaged over day, evening, and night periods with penalties applied to evening and night operations. International practice, guided by ISO 1996 and the EU Environmental Noise Directive, commonly uses the equivalent continuous A-weighted sound pressure level (LAeq) and the day-evening-night level (Lden).

Regulatory and Standards Framework

• GB 9660-1988: limit values for noise around airports, expressed in WECPNL
• GB 9661-1988: measurement methodology for aircraft noise around airports
• ISO 20906:2009: unattended monitoring of aircraft sound in the vicinity of airports
• ISO 1996-1 and ISO 1996-2: description, measurement, and assessment of environmental noise
• ICAO Annex 16, Volume I: aircraft noise certification and the Balanced Approach to aircraft noise management
• IEC 61672-1 and IEC 60942: performance requirements for sound level meters and acoustic calibrators

Testing Samples

For airport noise measurement, the "sample" is the acoustic environment at representative locations around the aerodrome. Representative measurement points are selected based on flight track distribution, land-use zoning, and the location of noise-sensitive receptors.

Airport Boundary and Flight Corridor Points

Measurement positions are established along extended runway centerlines and beneath typical departure and arrival flight paths, where the highest single-event levels occur. These points characterize the worst-case noise exposure from individual flight operations.

Noise-Sensitive Receptors

Residential neighborhoods, schools, kindergartens, hospitals, nursing homes, and cultural facilities within the noise-affected zone are prioritized. Points are placed outdoors in free-field conditions, with microphones positioned at least 3.5 meters from any reflecting surface other than the ground and at a height of approximately 1.2 to 1.5 meters above ground for attended measurements, or higher for permanent monitoring terminals.

Indoor Measurement Points

Where building sound insulation performance is evaluated, indoor measurements are conducted inside habitable rooms with windows in both open and closed conditions, using standardized facade measurement procedures to determine the indoor-outdoor level difference.

Permanent Monitoring Stations

Long-term noise monitoring terminals (NMTs) are installed at fixed stations around the airport per ISO 20906, typically mounted on poles or masts in open terrain, equipped with weather protection, and time-synchronized with airport flight information systems for event attribution.

Testing Items

Measurement programs typically report the following acoustic quantities and supporting parameters:

• WECPNL (Weighted Equivalent Continuous Perceived Noise Level), the compliance metric of GB 9660-1988
• LAeq,T: equivalent continuous A-weighted sound pressure level over defined measurement periods
• Ld, Le, Ln: long-term A-weighted levels for day, evening, and night periods
• Ldn / Lden: day-night and day-evening-night average sound levels
• LASmax: maximum A-weighted sound pressure level with slow time weighting, per flight event
• LAE: A-weighted sound exposure level per flight event
• LEPN: Effective Perceived Noise Level per flight event, including duration and tone corrections
• Number of classified aircraft noise events per period and event-to-flight correlation
• Background (ambient) noise level without aircraft events
• Meteorological parameters: wind speed and direction, temperature, humidity, barometric pressure, and precipitation

Testing Methods

Instrumentation and Calibration

All measurements are performed with sound level meters compliant with IEC 61672-1 Class 1 specifications, verified with acoustic calibrators meeting IEC 60942 Class 1 requirements. Field calibration is carried out before and after each measurement session, with acceptable deviation typically not exceeding 0.5 dB. Outdoor microphones are fitted with wind screens, and measurement is suspended when wind speed exceeds 5 m/s or during precipitation.

Unattended Monitoring per ISO 20906

Permanent or temporary noise monitoring terminals continuously record sound pressure levels and use event detection algorithms to identify aircraft noise events. Where flight track data from radar or ADS-B systems is available, each event is correlated with a specific aircraft movement, enabling attribution of measured levels to individual flights and validation against modeled levels.

Attended Short-Term Measurement per GB 9661 and ISO 1996-2

For compliance and impact assessment, monitoring is conducted over complete 24-hour cycles covering representative operational days, with a monitoring duration of one week recommended to capture day-to-day operational variability. Each aircraft event is recorded with its time history; the EPNL of each event is determined from the maximum perceived noise level, duration correction, and tone correction. Extrinsic noise from road traffic, construction, or other community sources is excluded from event analysis.

WECPNL Calculation

The weighted equivalent continuous perceived noise level is computed as:

WECPNL = LEPN,average + 10 log10(N1 + 3N2 + 10N3) − 39.4 (dB), where N1, N2, and N3 are the numbers of flight events during the day (07:00–19:00), evening (19:00–22:00), and night (22:00–07:00) periods respectively. The coefficients 3 and 10 apply penalties to evening and night operations, reflecting heightened community sensitivity.

Quality Assurance and Reporting

Measurement uncertainty is evaluated in accordance with ISO 1996-2. Reports include instrumentation details, calibration records, site descriptions with coordinates and photographs, meteorological conditions, event logs, time-history data, calculated rating levels, and a comparison of results against the applicable limits of GB 9660-1988.

Applications

• Environmental impact assessment for new airports, runway extensions, and capacity expansion projects
• Compliance verification against GB 9660-1988 limit values and delineation of noise zoning contours for land-use planning
• Validation and refinement of airport noise contour models and flight track concentration studies
• Design and evaluation of noise abatement procedures under the ICAO Balanced Approach, including preferential runways and departure routing
• Determination of eligibility for residential sound insulation and relocation compensation programs
• Investigation of community noise complaints and verification of night curfew or operational quota compliance
• Strategic noise mapping and action planning for major airports under environmental noise legislation
• Long-term trend monitoring of the acoustic environment around aerodromes

FAQ

What are the limit values in GB 9660-1988?

The standard classifies areas around airports with the following WECPNL limits: special residential zones not exceeding 70 dB; residential, educational, and cultural zones not exceeding 75 dB; mixed commercial-residential and commercial center zones not exceeding 80 dB; and industrial zones not exceeding 85 dB. Areas exposed above these values are subject to land-use restrictions or require sound insulation measures.

What is the difference between WECPNL and Lden?

WECPNL is based on perceived noise level and effective perceived noise level, which account for the spectral character and duration of aircraft noise, and it applies evening and night penalties of 3 dB and 10 dB in the energy summation. Lden is an A-weighted energy-average metric with 5 dB and 10 dB penalties for evening and night. The two indices are not directly interchangeable, and the applicable index is determined by the governing regulation.

How long should a measurement campaign last?

A minimum of one complete 24-hour cycle covering representative flight operations is required, while monitoring over seven consecutive days is recommended to capture variations in traffic volume, runway configuration, and weather-dependent operating patterns.

Can aircraft noise be separated from road traffic noise?

Yes. Modern monitoring terminals combine event detection thresholds, level-time pattern analysis, and correlation with flight track data to distinguish aircraft events from ambient community noise, ensuring that reported rating levels are attributable to airport operations.

Which laboratories can perform this testing?

Measurements should be entrusted to accredited third-party laboratories with calibrated IEC 61672-1 Class 1 instrumentation, qualified acoustic personnel, and demonstrated competence in ISO 20906, ISO 1996-2, and GB 9661 measurement procedures.