How Weather Affects Noise Surveys

We’re well-known in the UK as a country that has a tendency toward the wet! The country is renowned for its tendency to rainy and windy weather, and we also run the gamut of those less obvious but no less impactful meteorological changes, such as in atmospheric pressure and humidity.

It’s fair to say, then, that the UK suffers from some unpredictable weather conditions, despite being such a supposedly temperate part of the world. As Acoustic Consultants, this is an important consideration in the work we do. 

It’s vital to us that your noise monitoring results are accurate. But environmental sounds can markedly affect your noise level results and make them unreliable. The impact of these has to be carefully considered.

Working with experts at Acoustic Ltd, you’ll be assisted in taking account of these environmental factors and ensuring they don’t adversely affect the quality of the sound data you collect.

This article will explain what weather conditions you should monitor under and why – and the potential adverse effects of monitoring in unsuitable conditions. 

Timelines for getting reliable noise survey results

Our clients regularly ask what our timelines are for environmental noise surveys. Our response? It varies within the scope of the works, but we might look to survey for seven days. 

In an ideal world, we would monitor 24 hours a day, 365 days a year, and in all weather conditions, to get the most precise results. Unfortunately, this is not always possible – and it’s not just because we don’t want to stand around in the cold and rain year-round!

Ideal Conditions for Sound Monitoring

For reliable data, noise surveys are best undertaken in certain weather. We recommend you take your survey under the following conditions:

• Dry with no rain.
• Temperatures above freezing with no significant variation.
• Wind speeds of below 10 miles per hour.

The perfect weather conditions for noise surveys are sunny skies, with no wind. But let’s be realistic – when living in the UK, days like these can be few and far between, so we have to be more flexible.

To ensure we are monitoring under correct conditions, we use a range of weather forecasting sites including The Met Office, the BBC, and Weather Underground. However, these sites are not always 100% reliable. For the long-term surveys we deploy weather stations to ensure the data we obtain is correct.

Why should we monitor sound under dry conditions?

Noise monitoring should be undertaken under specific conditions first and foremost to ensure you obtain accurate noise data.  That’s the priority. However, it’s also important to ensure you are following the methodology of the British Standard you will be using for your assessment, such as BS4142:2014 and BS7445:2003.

For a residential scheme where you are addressing the impact of external noise on the development, adverse conditions result in a more onerous noise assessment. This in effect would result in additional mitigation, and cost to the client.

How wind affects your noise survey

When addressing external noise, high wind speeds are generally the most significant factor. This is because high wind speeds affect the low end of the noise spectrum. 

Sound travels, of course, in waves. Even winds at a moderate speed can create refraction of these sound waves – impacting the noise data collected.

Altitude, when considered alongside high wind, also creates variances in the sound waves. The way wind speed varies with altitude is called wind shear. 

Wind travels more quickly at high altitude, for several reasons – there’s less of the friction caused at ground level, by obstacles such as mountains, buildings, and plant life.  Winds are strongest when isobars are closest together, as the pressure gradient between high and low-pressure areas is a primary factor impacting wind speed.

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. The stronger the winds, the more acute the problem.

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 measurement positions near to trees can be affected by wind speeds much lower than these, from wind rustling through leaves and branches.

How rain and snow affect your noise survey

Rain and snow can also adversely impact your assessment. The sound of rain will obviously increase environmental noise levels – potentially masking the very sounds that your noise monitoring survey is trying to measure. Rain’s impact goes on after the downpour itself, too, as residual sounds such as cars driving through puddles, the spray created by vehicles driving over wet roads and the gurgle of water running through pipes, drains and gutters can all significantly increase the background sound levels.

Snow has a slightly different problem for noise monitoring. You’ll have noticed that environmental sounds appear muffled after snowfall. That’s because snow is naturally acoustically absorbent, and will reduce sound levels.

How temperature change, air pressure and humidity affect your noise survey

Climatic elements such as these have a significant, though less obvious, impact on noise. As humidity falls, for example, the sound level falls too. That’s because the speed sound travels at increases as humidity increases, because humid air is less dense than dry air.

Temperature also affects the speed of sound. Heat (like sound) is kinetic energy. When it’s warmer, molecules have more energy, so they vibrate faster. This allows sound waves to travel more quickly. 

Similarly, air pressure impacts sound. The greater the pressure change, the louder the sound, as the amount of air molecule compacting and expanding relates to the apparent loudness. 

Some sites are particularly prone to the influence of environmental factors, and even the smallest changes can dramatically impact the results of your sound survey. Expert knowledge can help you ensure you have enough accurate data, correctly analyse it, and draw accurate conclusions and recommendations from all the hard work that has been undertaken.

It is clearly beneficial to ensure noise monitoring is undertaken in the most optimal conditions. Here at Acoustic Consultants, we use weather stations and a number of Class 1 outdoor sound level meters to ensure we can make the most of windows of good conditions, deploying quickly to numerous sites once the forecast and conditions are favourable.

Get in touch today to book your noise monitoring survey

To book in for assistance with your noise monitoring survey, get in touch to book in today.