In this 3 part article, Acoustic Consultant Teli Chinelis discusses environmental noise monitoring and the steps you should take when conducting one.
The second part concentrates on noise monitoring techniques, the selection of receptors and consultation. You can catch up on part one here.
- Noise Monitoring Technique
The style of monitoring will depend on the type of noise survey undertaken and the information that is required. Sometimes fully manned noise surveying may be necessary (e.g. complaints investigation), however, in general, unmanned monitoring will usually be appropriate. With modern equipment, continuous monitoring over a few hours to a few weeks can be undertaken at multiple locations in order to review the fluctuations in the local sound environment.
In the case of long-term continuous monitoring (say over a few months), and if secure locations with a power supply and reliable internet/mobile connection are available, modern equipment can be utilised where the recorded levels are downloaded remotely, or even viewed online via a web-based platform. If required, alerts can be set up and even automatic audio[1] recordings can be set up to aid in the investigation (for instance, the sound level meters may record a minute of audio when a predetermined trigger level is exceeded, assuming there are no privacy issues).
If required, multi-channel systems capable of measuring several parameters in addition to noise levels can be utilised (e.g., vibration, dust, weather data).
In the case of unattended noise monitoring, and especially if the noise climate is complex and is not dominated by one source, or a specific source needs to be identified within a complex sound field, the use of conventional equipment may be cumbersome and potentially very time consuming (e.g. when having to listen back to lots of audio samples to try to understand the noise climate better). Moreover, such monitoring can be inconclusive in a lot of cases. For instance, how do you know that the noise affecting the nearby hospital is emanating from your construction site rather than from the one next to yours? Advances in signal processing have meant that state-of-the-art sound level meters can process more information than previously possible and therefore overcome some if not all of the constraints encountered with conventional sound level meters.
A recent development is the multi-channel microphone for environmental measurements, to help automate the location of noise sources. The directional 3D functionality enables, for example, aircraft to be picked out from normal community noise, identification of the direction of significant noise sources, and separate analysis of particular noise sources (say a road or railway is near your construction site, and you want to be in a position to only consider the noise coming from your construction site).
It should be noted that sometimes, it may be preferable to predict rather than measure environmental noise levels. For instance, the proposals may significantly change the existing levels and the assessors may be tempted to rely only on predictions. However, even in such scenarios, environmental noise monitoring in conjunction with extrapolation should be the preferred option. Assessors may gain assistance from any noise maps that have been produced for the area of interest, however, the assessment should not rely solely on such information and great care is needed to ensure that such maps are fully understood. Rather than trying to extract the exact noise level at a location, such maps may be more useful in providing information in relation to how noise levels change at different locations around the assessed area.
- Selection of Receptors
In order for Environmental Noise Monitoring to be effective, all relevant noise-sensitive receptors must be identified and it should be borne in mind that these will not have the same degree of sensitivity. Such sensitive receptors may include non-residential buildings, animals and even land areas.
The assessor must be able to identify the location of such receptors and assign different degrees of sensitivity, and examples of such receptors include:
- dwellings;
- schools;
- colleges;
- cemeteries;
- hospitals;
- commercial premises;
- libraries;
- surgeries;
- farms;
- health Centres;
- religious institutions;
- retail;
- light industrial sites;
- kennels;
- zoos;
- wildlife sites.
It should be noted that in some projects, the proposals may introduce new noise-sensitive receptors and as such it will be imperative to include such uses as potential receptors in the assessment and review the impacts of existing noise at these receptors.
- Consultation
It is advisable to consult the competent authority prior to undertaking any Environmental Noise Monitoring and even prior to defining the scope of the study. Of course, there may be specific commercial or other reasons for confidentiality and as such, such consultation may not occur (at least initially). It should be noted that although the local planning authority may have an environmental health department with expertise in noise, the competent authority may not be the relevant planning authority.
Consultation has the following advantages:
- receptors may be more readily identified, and their significance quantified (as far as possible);
- local concerns may surface;
- information on existing noise levels may be known and may be available;
- monitoring requirements may be identified;
- assistance with the surveys may be provided for instance, by arranging access, or receiving an agreement to place a sound level meter on a lamp post;
- agree on suitable receptor locations;
- agree on a methodology for the assessment of the impacts.
If you want to discuss anything you have read here please email [email protected]. Keep an eye out for part three, coming soon!
[1] Meaning recordings that can be listened back in contrast to sound or noise readings.
