BS ISO 5305:2024
Noise measurements for UAS (unmanned aircraft systems)
- Standard No.
- BS ISO 5305:2024
- Release Date
- 2024
- Published By
- British Standards Institution (BSI) GB / BSI
- Latest
- BS ISO 5305:2024
- Introduction
Background and Technological Evolution of Standard Development
With the widespread application of multi-rotor UAVs in photography, logistics, agriculture, and other fields, their low-frequency, broadband noise has an increasingly significant impact on humans and the ecological environment. Unlike traditional large aircraft and helicopters, multi-rotor UAS noise is characterized by strong directionality, multiple pure tone components, and broadband noise. Furthermore, its low flight altitude and complex operating conditions (hovering, takeoff and landing, cruise) render existing aviation noise testing standards such as ISO 3744 inapplicable. Therefore, the International Organization for Standardization (ISO) released BS ISO 5305:2024 in 2024, specifically for multi-rotor UAS with a maximum takeoff mass (MTOM) of less than 150 kg, specifying noise measurement methods in three environments: anechoic chamber, anechoic wind tunnel, and outdoor. This standard, for the first time, unified key aspects such as sound pressure signal recording, far-field condition verification, microphone layout, and uncertainty assessment, filling a gap in international UAS noise testing.
Core Testing Facilities and Comparative Analysis
Test Environment Applicable UAS Specifications Key Advantages Main Limitations Recommended Noise Levels Anechoic Chamber MTOM < 4 kg (lightweight); 4~25 kg requires far-field conditions Controllable environment, low background noise, can simulate hovering and low-speed flight Size limitations, maximum speed limited (< 10 m/s, test time ≥ 5 seconds) Lp,A (hovering/yaw), LE,A (takeoff and landing/cruise) Anechoic Wind Tunnel Suitable for high-speed flight simulation (e.g., cruise > 10 m/s) Can simulate high speed, large scale, or complex conditions High requirements for shear layer refraction correction; vibration-proof installation support is required Lp,A (95% confidence interval ±1 dB) Outdoor site MTOM 25~150 kg or high-speed flight No size restrictions; can realistically simulate flight trajectory Weather influence (wind speed, temperature gradient); background noise limitations Lp,A,Smax or LE,A (90% confidence interval ±1.5 dB) The standard emphasizes: The test environment should be selected according to the UAS mass, size, and flight speed. For example, an anechoic chamber is recommended for small UAS (<4 kg), while outdoor testing is preferred for large or high-speed UAS. Simultaneously, all environments must meet the **far-field condition**: microphone distance R ≥ 5DA (DA is the UAS diameter), and be verified by the inverse square law (compliant with ISO 26101-1). The standard specifies microphone layouts for different operating conditions: Hovering and Yaw: A 4-microphone method (adjusting the UAS position to achieve different observation angles) or a multi-microphone arc array (angular resolution ≤18°) can be used. Takeoff and Landing and Cruise: A fixed vertical or horizontal track is required, with at least 3-4 microphones covering observation angles from 0° to 135°. Outdoor Testing: Use a ground-mounted pressure microphone (WS2P/WS3P type) with a grounding plate ≥500 mm in diameter to correct for ground reflections. All measurements must be calibrated before and after using an IEC 60942 Class 1 acoustic calibrator, with a deviation ≤0.5 dB. For anechoic chambers, Table 1 gives the maximum permissible deviation for the inverse square law (e.g., 800~5000 Hz: ±1.0 dB). Wind tunnel testing also needs to consider shear layer refraction correction (based on the Amiet method). Implementation Recommendations and Considerations: Environmental Selection: Prioritize evaluating the UAS's maximum takeoff mass and flight speed. If the anechoic chamber cannot meet the required track length (e.g., at least 50 m for a cruise speed of 10 m/s), the test should be conducted in a wind tunnel or outdoors. Simultaneously, meteorological conditions such as temperature, air pressure, and wind speed must be recorded. Far-field condition verification: It is recommended to use a reference sound source (such as a point source in ISO 26101-1) to perform an inverse square law check at the predetermined UAS location. For pure tone components, refer to the example in Appendix C (1/3 octave band averaging can reduce interference effects). Uncertainty management: Clause 10 of the standard lists eight main sources of uncertainty (such as repeatability, microphone accuracy, position offset, etc.). In practice, the number of repeatability tests should be determined based on the target confidence interval (95% in an anechoic chamber, 90% outdoors). For example, in the example in Appendix G, a repeatability standard deviation of 0.62 dB is obtained through 5 repeated measurements, and combined with the position offset (δD=0.0156), a combined uncertainty of 0.63 dB is obtained.
Report Requirements: Item 11 details the data to be reported, including UAS model, attitude, test environment description, calibration records, and final noise parameters (such as A-weighted sound pressure level or burst).
BS ISO 5305:2024 Referenced Document
- IEC 60942 Electroacoustics - Sound calibrators
- IEC 61094-4 Measurement microphones - Part 4: Specifications for working standard microphones
- IEC 61260-1 IEC 61260-1: Electroacoustics - Octave-band and fractional-octave-band filters - Part 1: Specifications
- IEC 61672-1 Electroacoustics - Sound level meters - Part 1: Specifications
- ISO 26101-1 Acoustics - Test methods for the qualification of the acoustic environment - Part 1: Qualification of free-field environments
- ISO/IEC GUIDE 98-3 Uncertainty of measurement - Guide to the expression of uncertainty in measurement (GUM:1995). Extension to any number of output quantities
BS ISO 5305:2024 history
- 2024 BS ISO 5305:2024 Noise measurements for UAS (unmanned aircraft systems)
