Karen's blog post on our recent lidar paper

Karen Anderson has written a really nice blog post on our recent paper "A comparison of LiDAR approaches for vegetation and landscape characterization" (published in the open access Remote Sensing in Ecology and Conservation journal). Karen's blog "Weighing up the benefits and costs of waveform LiDAR", and hosted on the ZSL blog site, outlines some of the benefits of waveform lidar for ecology. Our work shows how waveform lidar can provide habitat measurements that just aren't available any other way. Karen concludes that the next few years are likely to see an explosion in applications of waveform lidar in spatial ecology.

An image from Karen's blog showing our TLS work in suburban Luton (taken from: http://www.zsl.org/sites/default/files/styles/wysiwyg/public/media/2016-05/Figure%203.png?itok=ckeELLou)

First results from Ankasa

Andy's been busy processing the Ghana data. First cut from this is a flythrough - low res at the moment but you can see the tower at the start, and the topography towards the end. This was ..... a challenge shall we say.

Andy's also pulled out the 17 largest trees in the ESA AfriSCAT RADAR footprint - and the poibt cluds, and the resultiung models, are shown below. Our initial estimate is that there's around 150 t C in these 17 trees, probably close to half of the total for the whole plot!

Point clouds of 17 largest trees in the plot, extracted automatically from the co-registered full point cloud. Colours are just to differentiate each tree (same below).

Initial results from fitting cylinder models to point clouds. Mostly looking good, and the volume estimates seem robust from the parameter variation.

More tree models to follow!

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.

Zebedee arrives

While we were away in Ghana, our new "toy" arrived, the ZEB-REVO hand-held TLS instrument (or Zebedee). I say "toy" because it's not - it's a highly-portable laser scanner, developed by CSIRO in Australia, with much lower power and range than our Riegl but with correspondingly much lower weight, hence the much greater portability. It's designed to be used on mobile platforms - cars, UAVs and the like; the platform in this case being our legs. The idea is that we can use it to augment the Riegl, combining both to provide additional information in environments where we may find it hard to move the Riegl around and/or where the understory causes a lot of occlusion. First tests show it's *very* easy to use, which is a key point. Also, so far I'm impressed with the SLAM software that automatically co-registers all the data into a single point cloud. It seems to work well as long as you capture enough objects & targets that the software can identify in post-processing. I'm really looking forward to getting it out into a real forest environment with the Riegl to start experimenting.

The Ginkgo trees in the UCL quad, done in around 1 minute, with ghost Lewis's everywhere.

A rather more careful and complete scan done by Phil of you know where.

An animation of a walking down Gower Street, done by Kim. And below, a quick look inside the Dept. from a walk out of the lab and down the stairs.

And finally .... Ewan's nice picture of two great minds at work. Look, how hard can it be, just switch it off and on again.

Kim's BES prize

We're all very proud of Kim, who was recently announced as the winner of the British Ecological Society Methods in Ecology and Evolution (MEE) RobertMay early career researcher award (see http://www.britishecologicalsociety.org/grants-awards/honours_awards_prizes/prize-for-the-best-paper-by-a-young-author/robert-m-may-prize/). Kim won for his paper "Nondestructive estimates of above-ground biomass using terrestrial laser scanning" (seehttp://onlinelibrary.wiley.com/enhanced/doi/10.1111/2041-210X.12301). The paper was the culmination of Kim's PhD work, and involved many of our long-term collaborators, and it was a key piece of evidence vindicating our approach to using TLS to estimate biomass. Kim's paper received quite a lot of attention when it was published, featuring on the UCL News front page amongst other places (see https://www.ucl.ac.uk/news/news-articles/1114/211114-laser-scanning-weighs-trees), and has already been cited 30 times in less than a year. I'm not surprised, and I've no doubt it will go on to be cited many times, given its groundbreaking demonstration of the maturity of TLS for biomass.

Ghana, March 2016

So here we go again! This time we're scanning in Ghana, as part of the European Space Agency-funded AfriSCAT project, using our lidar to characterise the 3D structure of a piece of the Ankasa Forest reserve. AfriSCAT is designed to provide RADAR measurements of tropical forest, in preparation for the launch of the ESA BIOMASS Earth Explorer satellite mission in 2020. BIOMASS is a P-band (70cm) RADAR mission, which will allow it to 'see' through dense canopies to the larger trunks and branches; shorter wavelength RADAR (and optical signals) can't see through the upper part of dense tropical forests. So the ESA team want to know what their RADAR is seeing, and that's where we come in!

The AfriSCAT P-band RADAR instrument on the tower in the Ankasa forest.

 We visited the site, with the help of collaborators from CMCC in Italy, along with our colleagues from Wageningen University, Alvaro Lau Sarmiento, Cornelis Valk, Harm Bartholomeus and Martin Herold. so we could operate two lidars of the same type, in order to move faster and reduce risk. This is the first time we think anyone's deployed two lidars simultaneously in a tropical forest like this. It involved a bit of planning and synchronising so we all use the same protocols, but it seems to be paying off in terms of what we can cover. Also visiting was Yadvinder Malhi, our colleague from Oxford, who's been working at the Ankasa site for some time (and in Ghana more generally), establishing several large permanent plots in overlapping the one we were scanning and nearby. Yadvinder is working with with Harm and Juha Suomalainen, also from Wageningen, to collect UAV data over the site. Yadvinder is particularly interested in the relationship between tree traits, and structure, and is using the hyperspectral UAV data combined with detailed measurements made by his ground team, to try and understand these issues. See some lovely examples of the UAV footage of the site on Yadvinder's blog.

L to R; Justice, Cornelis, Alvaro, Andy and Phil (standing).

The view from the Ankasa tower is pretty stunning, if a little hot in climbing.

The team, sitting on a buttressed root with the two lidars.

So far, data collection has been looking good, despite some pretty challenging terrain. The image below shows a slice through the plot, which illustrates the nature of the terrain in the plot. Scanning on slopes like this is hard.  The weather has held up - no rain and not too much wind so far - and other than a bit of sunburn, so far nothing too tricky in the way of hazards. We didn't see a single mosquito in a week. Result!

An example of a slice through the AfriSCAT footprint plot showing the scan locations on the slope. The colours are reflectance i.e. brighter colours represent higher scattered lidar energy.

Below we can see another example of the lidar data from the AfriSCAT plot, from two scan lines, and joined together by Andy.

A slice around 70m long and 5m deep through the plot, coloured by height up to around 40m for the tallest trees.

Our research here has been funded primarily by ESA as part of the BIOMASS mission, but also in part by NERC through our involvement with NCEO and a recent Standard Grant award for tropical forest measurements.

More scanning at Kew ....

I went back to Kew yesterday to scan the Oriental Plane with its leaves off. It was a glorious sunny day, with almost no wind so ideal for scanning.

There's really not many more beautiful spots in London on a sunny day.

The famous Kew Orangery. 

The Oriental Plane is still standing, as it has for 250 years or more I guess. Albeit with a little help these days, in the form of wires and guys.

Oriental Plane at Kew Gardens.

Here's a first look at the lovely tree. Points are a bit large so it looks leafy, but it's not.

View up through the trunk from below the point cloud. Note the guy wires to the left and upper centre.

Viewing it like this makes me think 'brain'. Thanks to Andy for pulling the data off the lidar and registering it - literally within a few minutes of me getting back to UCL! This image highlights a couple of things - first the precision of the measurements that easily catch the 5mm diameter guy wires. And second, the accuracy of the registration in that the wires are not 'ghosted'. The fact that there was no wind certainly helps in this case.

The other reason for being at Kew was to film some more footage for the latest ESA MOOC (Massive Open Online Course), this time on optical remote sensing. The last one, Monitoring Climate from Space, seemed to be successful. So I've been asked by the production team to contribute to this new one, and scanning trees in Kew makes a great backdrop to talk about forests, land use and how we can use EO and other new technology to make sense of it all.