Thursday, 17 July 2014

Summer of scan 2014: Wytham Woods, Oxfordshire

A new opportunity to work at a piece of old English woodland came up earlier this year - Wytham Woods. This is a lovely 400 ha area of semi-natural, old woodland, just outside Oxford in the quintessentially English countryside, within sight of the banks of the Thames. The woods were bequeathed to Oxford University in 1942 and are now home to a range of scientific research activities into the fauna and flora.

We are working with Prof. Yadvinder Malhi and his team at Wytham, to scan the established forest plots and estimate above ground biomass, as well as measure the structure of the trees. This is part of our ongoing work using laser scanning to characterise forest state. A really interesting thing about the work at Wytham is that Yadvinder has established plots which he is using to replicate the work he does in the tropics through the Global Ecosystems Monitoring (GEM) network, characterising the tree and plot traits (plant biochemistry) and function via ecophysiology measurements including C fluxes, soil and water properties.

The TLS instrument in leafy Wytham, on a calm midsummer's day. Only the mosquitoes for company.
We aim to scan a section of Wytham within the SIGEO 18 ha plot, and characterise all the trees in 3D. We have scanned one part of this so far, and aim to return over the coming months to do leaf on, leaf off, and then repeat over the next few years. Another interesting aspect of the infrastructure at the Wytham plot is there is a tall canopy walkway. We are thinking about how we can scan from there to to really capture in fine detail the upper part of the canopy, which we do less well from the ground.
Walkway infrastructure at Wytham Woods.
From the top looking down, with John Armston (U Queensland/Queensland Govt) looking up through the oak, ash and sycamore canopy.

Wytham will also form part of a separate EU-funded project, working with the National Physical Laboratory (NPL), which will deliver tools for doing calibration and validation of satellite-derived estimates of leaf area index (LAI) and fAPAR, which characterise the amount of leaf area, and the canopy absorbed radiation respectively. These key canopy properties are needed for understanding and modelling forest state and function, are widely-used but actually very difficult to measure in practice. As a result, validating (testing the quality of) satellite-derived estimates is also very hard, as we don't know the real values at anything other than very small scales (few m). One way to address this is to build very detailed models of the landscape, and then simulate what satellites and ground-based observers would see, where we know the LAI and fAPAR in advance. This is what we are aiming to do at Wytham, using the laser scanner to build 3D models of a section of the woodland, that we can use as a surrogate, model testbed for testing and validating new satellite measurements of LAI and fAPAR, among other things.
Watching you watching me watching you. A crowd gathers to watch the scanner do its thing in Wytham.