A new discussion paper from the Met Office and the National Physical Laboratory (NPL) highlights the practical challenges of understanding the performance of autonomous vehicles (AVs) in different weather conditions. 

The paper draws from an ongoing project conducted by the Met Office and NPL and is funded by the UK’s Centre for Connected and Autonomous Vehicles (CCAV). 

This Sensor Assurance Framework (SAF) project aims to create a reliable and usable framework for understanding how well AV perception sensors (the eyes and ears of the vehicle) perform in different weather-related conditions. When fully developed, this framework will support validation, safety assurance and simulation testing of AVs across the UK.   

Central to SAF project has been the Cardington weather-sensor testbed, which has accumulated over two years of detailed weather measurements and corresponding AV sensor measurements as they observe targets set up at varied distances in a wide range of weather conditions including fog, intense rainfall, clear and cloudy skies and direct sunlight. 

Met Office Observations Principal Consultant Dave Jones, who is part of the team leading the weather measurement side of the Cardington testing, said: “The effect of weather on sensor performance is very complex and it is challenging to reflect this when trying to capture the weather envelope for the AV as simply as possible. 

“This discussion paper gives examples of how this complexity reveals itself on our testbed and how we might begin to handle this by careful consideration of uncertainty.  We are very interested in hearing views from everyone in the wider AV community involved in safety assurance.” 

National Physical Laboratory’s Andre Burgess, who looks after strategic partnerships, said: “As well as the scientific and technical aspects of our joint SAF project, we are placing a huge emphasis on engagement with regulators, industry, standards bodies and academia to ensure that these testbed results make a positive difference to the AV industry and public safety.” 

The discussion paper comes as the Automated Vehicles Act became law this week and paved the way for self-driving vehicles to be possibly on the UK’s roads as soon as 2026.

Ongoing research 

The Met Office and NPL’s Sensor Assurance Framework research at Cardington has been undertaken for around two years, with the aim to test sensor performance against as many different weather types as possible, including rain, hail, sunshine and fog.  

The research so far demonstrates an observable relationship between weather conditions and sensor performance, though further study is needed to fully understand this area, including the impact of different locations, road surfaces, vehicle movements and a broader range of weather types. It’s hoped this research will help the autonomous vehicle industry to develop further in the coming years.  

The Met Office and NPL will continue collecting weather data and assessing sensor performance in the coming months, with a new testbed at NPL’s headquarters in Teddington and plans to develop a relocatable testbed which can be deployed in a wider range of weather conditions.  

The SAF principles also extend to marine autonomous vehicles. Plans are already well underway to build a demonstration testbed around Plymouth Sound UK, as part of the Maritime Autonomy Assurance Testbed (MAAT) project, which is lead by NPL and Lloyds Register with partners including the Met Office, Plymouth Marine Lab (PML), University of Plymouth, and Warwick Manufacturing Group (WMG). 

Read the AV and weather discussion paper on the NPL website.  

Find out more about the Met Office’s services with Connected and Autonomous Vehicles.

It will be no surprise for many to hear that April 2024 has been a wet month. In what has felt like an unsettled spring so far, the UK has had its sixth wettest April since the series began in 1836, according to provisional statistics from the Met Office.  

Sunshine has been in short supply, with the UK provisionally recording just 79% of its long-term average for the month.

Wetter than average

The UK experienced 55% more rainfall than an average April, with 111.4mm falling across the month, making it the sixth wettest April in the series and the wettest April since 2012.

Many areas recorded more than their long-term average monthly rainfall, with Scotland experiencing its fourth wettest April in a series which started in 1836. It saw 148.9mm of rainfall across the month – more than 60% of its average and the wettest April since 1947.

Some places in Scotland saw more than double their average rainfall for the month. Edinburgh in particular saw very large rainfall totals, receiving 239% of its average April rainfall, which is its second wettest on record, falling only behind totals in 2000. East and West Lothian, Aberdeen, Clackmannan, Berwickshire and Cumbria, among others, also recorded more than double their average rainfall in the month. A rain-gauge at Honister Pass in the English Lake District recorded more than 400mm of rain.

Met Office Scientist Emily Carlisle said: “April has been a continuation of the past few months: often wet, windy and unsettled. April showers were present from the beginning of the month, with frontal systems bringing persistent precipitation across the UK. Although a high-pressure system moved over the UK on the 20th bringing some drier weather, by the end of the month, low pressure was back in charge, bringing with it more rain.”

Temperatures around average

April was a month of two halves when it comes to temperatures. The month started off warm, particularly along the southeast coast of England. Writtle in Essex recorded 21.8°C, making it the hottest day of 2024 so far in the UK.

Temperatures then dropped, remaining slightly below average for most of the last two weeks of April. This balanced out the warmer temperatures at the start of the month and resulted in a provisional average mean temperature of 8.3°C for the UK, only 0.4°C higher above the 1991-2020 long-term average.

Cloudy conditions often resulted in overnight temperatures being held up, with the average minimum temperature being above average (+0.8°C).

A dull month

Along with being a wet month, April has also been a dull month. The UK provisionally recorded 79% of the long-term average sunshine duration, with 122.9 hours.

One named storm

April saw Storm Kathleen arrive on the 6^th, bringing heavy rain to Scotland, Wales, parts of Northern Ireland and the west coast of England. Kathleen also brought strong winds across the UK, with gales along coasts, particularly in the north and west of the UK. Kathleen was the eleventh named storm of the 2023/24 season. This is only the second time that the Met Office has reached the letter K since they began naming storms in 2015.

Spring so far…

Meteorological spring (March to May) so far has been wet. Both England and Wales have already seen more than their long-term average rainfall for the entirety of the season, while the UK has seen 96%. At this point in the season, we’d expect to see 66% of average.

Provisional April 2024	Mean temp (°C)		Sunshine (hours)		Rainfall (mm)
	Actual	Diff from avg (°C)	Actual	% of avg	Actual	% of avg
UK	8.3	0.4	122.9	79	111.4	155
England	9.3	0.6	127.0	78	85.5	152
Wales	8.5	0.4	113.3	72	135.8	154
Scotland	6.6	0.0	119.2	84	148.9	160
N Ireland	8.3	0.3	118.4	80	104.6	141