Puéchabon webcam

January 29, 2012
Webcam installation

One of the things I’m responsible for in my day job is a phenology webcam at our experimental site at Puéchabon. The idea of this is to observe colour changes in the canopy of the forest up there, with a view perhaps eventually to replacing manual phenological observations with information drawn from digital photos. In this sense, phenology means things like when flowers come out, when fruit forms, and so on. The Quercus ilex (holm oak) forest at Puéchabon is evergreen, so you don’t get the same spectacular seasonal changes in leaf colour that you see in deciduous forests, so we’re not sure whether this is going to work – the changes we’ll be looking at will be a bit more subtle.

We installed the webcam on the 20 metre tower at Puéchabon in July and have been collecting images every half hour since, apart from a few outages. The images aren’t all that exciting (below left), but it’s quite nice to watch the changing angle of the sun on the canopy throughout the day. Very preliminary data analysis indicates that we will at least be able to see something changing through the seasons, even if it’s not abundantly clear to the eye from the images. A recent paper by Sonnentag et al. (unfortunately behind the evil Elsevier paywall…) gives some ideas about how to analyse these images. In the plot below right is a time series of the mean chromatic green component of the part of the webcam field of view that covers the forest canopy. This is defined as gcc=G/(R+G+B)g_{cc} = G / (R + G + B), where RR, GG and BB are the red, green and blue components of the digital image. There is definitely some seasonal variation, although with a lot of noise. I want a full year of data, so that we can see the new growth in the spring, before doing some more detailed analysis, since there are definitely still some scene illumination artefacts in what we’re seeing. It’s encouraging that we can at least see something though!

Webcam image

Webcam image

Chromatic green time series

Chromatic green time series

The potential difficulties in data analysis aren’t helped much by the local criminal low-lives. We’ve had four major thefts at Puéchabon in the last six months, the latest of which involved break-ins at both of the sheds on site and theft of a load of gas analysis and data processing equipment (including the PC collecting the webcam images), as well as power conditioning equipment and batteries used with the generator we use to power the site. Until the third theft of the year, we did have a nice big set of photovoltaic panels for power, but some enterprising lads took a truck up there and carted them all away. Probably 20 square metres of panels, gone in one night. It’s pretty weird. Much of the stuff these idiots have taken is basically worthless to them. It’s hard to imagine them successfully fencing a gas analyser or a fluorometer at one of the local flea markets! They seem to be taking stuff just because it’s there and it’s shiny.

It’s not quite clear what’s going to happen at Puéchabon now going forwards: we can’t afford to have guards at the site 24 hours a day to protect stuff, and it’s getting kind of silly when Alain and Jean-Marc, the technicians who go up there weekly, come back more often than not with long faces and another tale of broken locks and missing stuff. The whole point of a site like this is to have continuous observations, and if those keep getting interrupted by equipment walking away, it reduces the value of the remaining data quite a lot. We’ll have to see what happens.