Posted: 15th December 2021

How weather conditions affect noise survey results

It’s fair to say that Britain is well-known for its unpredictable and sometimes wild climate! Wind and rain are commonplace throughout the year, while less discernible changes – for example, in atmospheric pressure or humidity – are also frequent.

When conducting noise monitoring, it’s important that results are accurate and reliable. Unfortunately, results of environmental sound level surveys can be affected by meteorological factors, which, if not properly considered can have a material impact on the outcome of any subsequent acoustic assessment.

Partnering with a professional, experienced acoustics expert will help to prevent environmental noise from adversely interfering with the results of a sound level survey as they’ll be able to consider all the factors when assessing the data that has been collected. So, how can the weather conditions affect the results of a noise survey?

Wind

Sound travels in waves, but even a moderate wind can instigate refraction, or the bending of these sound waves. At higher altitudes, wind currents travel more quickly than at lower levels, due to natural undulations in the landscape and features such as trees and buildings causing the wind to travel more slowly. This causes sound waves to bend downwards when travelling downwind from the noise source, and upwards when travelling upwind. This can significantly alter the perception of noise volume and, the stronger the winds, the more acute the problem.

In simple terms, in moderate to strong winds the sound level will be louder or quieter depending on the location of the source and receptor, in relation to the direction of the wind.

Wind speed will also impact measured sound levels. BS 4142:2014+A1:2019 recommends that microphone windshields are effective up to wind speeds of 5m/s and the consultant should exercise caution above this speed. However, sound levels at measurements positions near to trees can be affected by wind speeds much lower than these from wind rustling through leaves and branches.

Rain and snow

Rainfall will naturally increase noise levels, potentially obscuring the sound that the noise monitoring is trying to measure. Even if rainfall has ceased, residual sounds are likely to remain that prevent accurate measurement, such as cars driving through puddles, the spray of water from wet roads as vehicles travel over them, or running water in pipes and gutters.

Snow also poses a potential problem in noise monitoring. Many people are familiar with the sense of environmental sounds seeming muffled after snowfall. Snow, as a porous substance, is a natural acoustic absorber and will reduce sound levels particularly from sources outside the immediate vicinity of the receptor.

Temperature, air pressure, and humidity

Although less obvious to the casual observer, other climatic elements – temperature, air pressure, and humidity – also affect the way that sound travels, particularly when the noise source is further away.

For example, a relative fall in humidity from 80% to 20% could decrease the sound level by up to 3dB at a distance of half a mile. Comparably, an increase of 20°C at a stable humidity would increase the sound level at the same distance by 3dB.

Some measurement sites are particularly susceptible to the influence of environmental factors and subjectively relatively small changes to weather conditions can affect sound level survey results. Without expert knowledge this can potentially lead to inaccurate analysis of the data and incorrect conclusions and recommendations.

For reliable noise assessments, contact ACA Acoustics

At ACA Acoustics, we have the expertise and know-how to ensure that the weather doesn’t pose a threat to the accuracy of our noise monitoring and that you can rely on the outcome of our assessments and recommendations. To enquire about our services, call us on 01793 766324 or send us a message.

Image Source: Unsplash

Posted By:ACA Acoustics

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