In March 2021, myself and colleagues from the universities of St Andrews and Aberdeen undertook fieldwork in the Scottish Highlands to map snow-covered terrain using a new, ground-based millimetre-wave radar. We collaborated with the Scottish Avalanche Information Service (SAIS) to assess the capabilities of this new instrument in evaluating snow-associated hazards such as avalanches. This project has been funded through the Gray-Milne Travel Bursary through the British Geophysical Association (BGA).
But, wait, 2021? Really? We’re in the middle of a pandemic! Well, this is the story of how we were able to conduct fieldwork during the coronavirus pandemic and battle the Scottish winter.
I’ll spare you the details of how we implemented the well established coronavirus regulations. What I would say though is that this fieldtrip was unique – I doubt fieldwork was ever planned so meticulously before. Every action, every possible interaction with an external member of the field team had to be assessed in advance to remove any potential risk of coronavirus transmission and I have to say the University of St Andrews were immensely helpful in this respect. Safety is paramount and adaptation is necessary – I led my field team with this firmly at the forefront of my mind.
Now on to the interesting part, the field campaign! Our objective was to map snow cover in the Cairngorms, Scotland, using millimetre-wave radar and a Terrestrial Laser Scanner (TLS), validated with in situ measurements of snow properties. Millimetre-wave radar uses a higher operating frequency compared to other radar instruments and so can map terrain at high-resolution and in most weather conditions. This could be a game-changer for the SAIS who currently rely on arduous and potentially dangerous fieldwork to evaluate avalanche risks.
So, whilst our objective for this fieldwork was relatively simple, planning the fieldtrip was anything but. And no, it was not the pandemic that was the biggest hurdle to our fieldwork, it was in fact (drum roll please!): the brilliantly, unpredictable Scottish weather! Time for a quick review of the 2020-2021 Scottish winter.
In early February, Scotland was hit with a ‘Beast from the East #2’ style cold spell, leading to widespread snow cover across the hills and lowlands. Within 2 weeks, that cover diminished to just a smattering of snow over high-ground. You can see this in the satellite images below – Scotland was white for the first part of February, but this soon vanished as an extreme temperature shift melted much of the snow away. Other’s will be able to explain the climatic phenomenon that took place, all I can say is that where I live, ~10 cm of snow in my garden melted away on a single day. That has to be classed as uncommon and extreme?! For the remainder of February and March, myself and the field team played a waiting game to see if any of that snow would reappear, but we were fighting a losing battle. Luckily, the Scottish Highlands maintained a significant snowpack above 900 m and we jumped at the last possible opportunity in late-March to measure it with our instruments.
In itself, the extreme melting of snow in Scotland was a driving factor behind our fieldwork. Understanding how these climatic events influence snow cover is vital for local communities and for the safety of those working across the Highlands. As we have seen, patterns of snow melt and accumulation can be dramatic in Scotland and this has significant impacts on local ecosystems, upland hydrology and snow-associated hazards.
However, mountain regions are renowned for their changeable weather conditions. The image below shows a situation in which cloud obscured the summit of Cairn Gorm, Scotland. In these conditions, we can’t use satellite imagery or cameras to map the snow cover, whilst the poor visibility may also be dangerous for SAIS forecasters to carry out their field measurements. This is where radar is seen as a solution to these issues because it can image through the cloud and hence be used as a tool for operational snow monitoring.
Our particular solution is to use millimetre-wave radar, which operates at the higher frequency end of radar systems. In general, frequency scales with resolution and so operating at a higher radar frequency means you can map terrain at higher resolution. In addition, we also deployed a TLS instrument to validate our radar measurements. This multi-sensor deployment was a pretty cool and unique set-up!
Overall, fieldwork was very tricky – we had to contend with very strong winds throughout and you can see in the image below that both instruments were tied down by as many rocks as we could find (n.b. car batteries can be used as a pretty good anchor)! I still couldn’t help running to the instruments every time a strong gust raced through our field site – this did raise a few eyebrows amongst the field team.
The instruments were deployed in the car park of the Cairngorm Mountain ski centre and a massive thank-you to Jim and the team for helping us out with this deployment. Our scene covered the ‘northern corries’ (see image below) – to the left we have Corrie Cas, which sits above the ski centre, in the centre is Fiacaill a’ Choire Cas and to the right is Coire an Lochain. Snow cover was largely restricted to the headwalls of the corries, with scattered snow patches below.
The large snow accumulations in February was retained across the headwall of Corrie Cas (see image below), due to a combination of shadowing and wind drift accumulation from the plateau above. According to the SAIS, cornices were present in the region across the headwalls of both corries and could represent a hazard as the temperatures swing dramatically either side of freezing.
And in fact, the snow was mobile during our fieldwork – small streams of snow fell from the top of Coire an Lochain overnight due to significant wind accumulation on the corrie rims. Our job now is to see if this appears in the radar data! This was really interesting because I had never considered how dynamic snow could be at the end of winter.
The constant melting and freezing of the snowpack over the course of the winter had led to a mostly stable snowpack with large snow grains. As an aside, I found fingerless gloves VERY useful for writing notes in the cold!.
This trip was a great success and it couldn’t have gone ahead without the full backing of both St Andrews and Aberdeen universities, the generosity of Cairngorm Mountain ski centre and the unwavering support of the SAIS. A big thank-you to Mark Diggins (SAIS Co-ordinator) and Blair Fyffe (SAIS Forecaster) for helping us in the field, we couldn’t have done it without them!
So what comes next? You can keep up to date with this (and others active projects) through my twitter feed and this website. Some preliminary results will be shared with the community at vEGU21. This fieldwork was an experiment to see what millimetre-wave radar can be used for in terms of snow mapping. I think there is an exciting future for this instrument and I’m sure we’ll be back to develop this technique further.
Will Harcourt (featuring extreme lockdown hair!), PhD Student, University of St Andrews