The importance of ‘groundtruthing’

‘Groundtruthing’ is a concept that was introduced to me by an ex-girlfriend who just happened to be an ecologist but it’s such an ugly neologism that I was initially sceptical that it meant anything useful at all. In fact, as she patiently explained, it means the process by which the accuracy of scientific data from satellites is verified by making direct observations on the ground. What has all this got to do with photography? Well, these days, thanks to the Internet and more specifically ‘Google Earth‘, we all have easy access to high-quality satellite and aerial imagery. I would be very surprised if most people reading this hadn’t already used Google Earth to assist in the planning of a photography trip at some point, so this isn’t really about the software product, as such. It’s more a cautionary tale about how too great a reliance on aerial imagery can be a Bad Thing…

Gorge de la Sirène

Before my most recent trip to the French side of the Jura, I spent a little while with Google Earth, just to see how sunlight interacts with the terrain and to work out at which times of day various features might be lit or in shade. That’s when I happened, quite by chance, on the heavily-wooded Gorge de la Sirène.

I love a good gorge, especially if it’s covered in lush vegetation, and when I saw how few photographs from this spot had been put on Panoramio I realised that this was no over-photographed honeypot location. Great! I always like to get away from people when I’m out making photographs – fewer distractions usually mean better pictures, especially if the ‘distractions’ are other photographers!

Anyway, the big problem with aerial photography is that it can’t see through trees in full leaf so it was very hard to even follow the course of the river let alone to pick out individual features like waterfalls or where the gorge narrows. There seemed to be a road in from the bottom end which terminated at a small car-park so it was starting to look promising. A little more digging, plus some cross-referencing with Google Maps (not to mention a more traditional ‘hardware’ map) led me to the upper entrance and an adjacent field with a flat area that looked like it might double as another carpark, should the need arise. Aha! Infrastructure! This means easy access via a footpath and some relaxed photography, I thought. Well, since I’m writing this post about ‘groundtruthing’ and not about a pleasant stroll in the country, you might imagine I was mistaken. Dramatic pause, Jeremy Clarkson voice. And you’d be absolutely right.

Impassable barrier

On arrival at the lower end, I decided a quick recce would be in order so I grabbed my digital gear and my tripod and set off. Thinking the track I saw disappearing into the trees would be easy, I didn’t even bother to change into my hiking boots. Big mistake. The track was crossed by a couple of very shallow side-streams which needed to be forded. Not a big problem. I then needed to duck under or over a couple of fallen trees and that’s when I saw this beech tree, obviously recently fallen, which, lacking a scythe, machete or chain-saw, proved to be an impassable barrier. Luckily, there was evidence of a footpath which left the track and headed off into the woods in roughly the direction I wanted to go, so I followed it. After only two-hundred metres or so, the sides of the gorge started to steepen and close in. Huge boulders had collected in the river from landslides and the gradient ramped up viciously. The river itself crossed this barrier in a series of cascades and deep plunge-pools and the path itself….errrm, stopped. That was it. No steps cut into the rock to aid weary hikers. No picturesque wooden bridges. Nothing. Still, I could see a particularly photogenic waterfall at the top of the rocks and I hadn’t come all this way to give up just when the going got tough. So, I started to pick out a route. Scrambling over a couple of boulders, I could see that I’d need to cross the river as the going looked marginally easier on the other side. I found a fording point and gingerly crossed over. Scrambling up the steep bank, I finally realised why the gorge is so under-photographed. Access is downright difficult and further progress from this point is well-nigh impossible without a willingness to get one’s feet wet. This being mid-Spring, I didn’t fancy taking my shoes and socks off (besides that would only lead to bruised and bloody feet from all the rocks and stones) so I turned back. Fortunately, in the car I not only had my trusty hiking-boots but also some fisherman’s waders (the ‘breathable’ sort that allow for comfortable hiking). I decided to return the next day. In the meantime, I drove to the village that marks the upper end of the gorge, found the field I saw on the Internet and parked the car. I reasoned that if bottom-up access was so difficult, there must be an easy top-down route. I quickly found the river and two concrete lamp-posts that were laid across it as a makeshift footbridge. Now we’re talking! But no. The path stopped about a hundred metres downstream, just before some low cliffs which went straight into the shallow river: obviously going in from the top would also mean some wading. By this time, it was already late and I needed to find a bed for the night – not to mention a decent meal – so I abandoned.

The route to the waterfall

In the end, I returned to the lower access point (better the devil you know…) two days later. I got into my waders, grabbed my digital kit for lightness and maximum agility and set off with high hopes. Being able to splash through the river was a boon and I quickly found the point at which I’d previously turned back. Here, there was a deep plunge pool, far too deep to wade. Luckily, a stout tree had fallen across the river a short way downstream so I nervously inched across, using an outstretched tripod leg for balance. The drop on the downstream side was around ten metres and I hadn’t seen another person in all the time I had so far spent in the gorge! At this point, I did question why the hell I was doing this and putting myself in such a tricky situation for a mere photograph but I can be an obstinate s*d when I want to be, so I pressed on… Climbing the stream-bed was not easy and meant some decidedly ‘technical’ scrambling over slippery moss-covered rocks but I did get to the waterfall (although I could see I’d need a dry suit and climbing gear to make further progress upstream) and I did get my picture.

Retracing my route back to the car, I quickly realised that that was enough excitement for one day and finding a top-down route would have to wait for another visit. So, what conclusions can we draw from this? Well, firstly, don’t give up at the first major obstacle – come back when you’re better prepared. Secondly, breathable fisherman’s waders, or even a dry-suit, are useful things to have if you enjoy taking pictures near water! And finally, don’t put all your faith in Google Earth! It doesn’t tell the full story….

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2 Responses to The importance of ‘groundtruthing’

  1. Very entertaining, Julian.

    I’ve used Google Earth for – I now learn – ‘groundtruthing’ a few times and it’s certainly not without an element of imprecision, particularly when it comes to areas cunningly hidden in trees and valleys. In fact, what with TPE to plan relatively precise lighting conditions, and Google Earth’s ‘ground level view’ to get an idea of what things will look like from any given location, I think I’ve once or twice spent more time at a screen, planning a shot, than I have in walking to a GPS location I’ve pre-defined and actually capturing it.

    That said, I don’t trust either fully when there are trees around and you’ve confirmed my suspicions in that respect 😉


  2. I didn’t know that.

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