Thursday, 28 April 2016

Winter, summer, ground, air ....

Kim has been working on the airborne lidar data over Wytham, provided by David Coomes and co at Cambridge, and originally collected by NERC ARSF as part of the AIRSAR campaign. The data were collected on 24th June 2014, so leaf on and a year before our ground campaign. The image below shows the airborne lidar data over a ~100m transect across Wytham wood.
NERC ARSF lidar collected over the Wytham site, 2014.
 It's immediately obvious the difficulty that even this dense, high quality airborne lidar sensor has in seeing through the canopy. But this is also a lovely example of the power of lidar to show the vertical structure and density of the canopy the layering, and the range of heights over the ground. Below we see the same airborne data overlain on to the TLS summer (leaf on) data. It's worth emphasising what a good job Kim's done in manually overlaying these datasets to get the agreement we can see.

TLS data (green) collected summer 2015 (leaf on) overlaid on to the 2014 summer ALS data.
 Now we can see: how well the two datasets match up, but also the massive amount of detail that is missed when you look down. Clearly, the trade-off is the time and area you can do this. But what a fantastically rich dataset illustrating the canopy structure. We also have of course the leaf off TLS:
TLS data (red) collected winter 2015/16 (leaf off) overlaid on to the 2014 summer ALS data.
Again, this shows beautifully the profile of the canopy, but also how much more we see in winter than in summer of the upper branches. Unsurprisingly! As far as I'm aware no one's ever collected a dataset quite like this with the detailed TLS, ALS and then the spectral and biophysical data. We're all looking forward to exploring these data in more detail in conjunction with the spectral and spatial analysis with David's group, even radar, and the ground-based trait data collected by Yadvinder. And even the aerial photography is a thing of beauty ;-)
Aerial photograph of the Wytham site, with the lodge visible in the centre and the walkway just visible directly above the lodge towards the edge of the image.


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