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UCL Home  /  Geography  /  Blog  /  Blog Entries  /  New adventures in LiDAR: a summary of the year at UCL

New adventures in LiDAR: a summary of the year at UCL

Posted by Ajay Chauhan at Dec 22, 2016 02:36 PM |

by Phil Wilkes (PDRA, NCEO and Department of Geography, UCL)

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Who is hiding in the bushes? Mat Disney and the RIEGL VZ-400 scanning the BIOMASS validation plot, Ankasa, Ghana (March 2016).

I recently wrote a blog article for the BES Methods in Ecology and Evolution journal espousing the applications and benefits of LiDAR, in particular airborne LiDAR for the assessment of forest structure over large areas.  The article focused on airborne acquisitions as this has been the most prolific use of the technology in forest ecology over recent years.  However here at University College London we are now combining 3D measurements captured across a range of scales, from handheld laser scanners to (soon to be launched) spaceborne sensors on the International Space Station, to create highly detailed measurements of forest structure which are applicable to a number of contemporary environmental issues.

Over the past 12 months, the UCL team have been busy deploying instruments in Ghana, Gabon, Brazil as well as closer to home in Northumberland, Oxfordshire and Kew Gardens, for a range of projects including: NERC-funded work on GREENHOUSE and a standard grant aimed at assessing tropical forest biomass; the EU-funded METEOC-II project in conjunction with the National Physical Laboratory (NPL) developing new ways to quantify uncertainty in EO measurements; ESA-funded calibration and validation in support of the BIOMASS and NASA GEDI missions. This blog article will summarise some of the highlights.

Different scales provide different perspectives

The department have recently purchased a GeoSLAM ZEB-REVO, a handheld laser scanner used for rapid characterisation of forest structure. Being mobile allows you to wander through the forest collecting 3D measurements which are useful for quickly locating stem positions and dimensions as well as creating digital elevation models.  This has proved particularly useful in forests where dense vegetation can make more traditional inventory methods time consuming.

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A walk through Wytham Woods with a GeoSLAM ZEB-REVO. The blue track is the path taken by Kim Calders and the points are LiDAR returns which are coloured by height.

To create highly detailed 3D models of individual trees, our RIEGL VZ-400 is required. Although this takes much longer to complete a scan the level of detail acquired is exceptional and almost consistent all the way to the top of the canopy.  There are a number of uses for such detailed data including the accurate estimate of tree volume (and by extension biomass), understanding tree function as well as tree reconstruction for purposes of creating virtual forests.

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From the bottom to the top of this 35 m+ tropical tree (captured earlier this year in Ghana) the level of detail captured using TLS is high. The mean nearest neighbour (nn) distance shown here illustrates that even towards the top of the canopy returns are <4 cm apart. (Image taken from an upcoming publication on TLS field protocols).

This year we have taken our scanner across the globe to Ghana and Gabon in Africa to scan Global Ecosystem Monitoring network plots in conjunction with the European Space Agency BIOMASS project, to the Brazilian Amazon (as part of the AmazonFACE project) as well as closer to home in Northumberland and Kew Gardens. This year also saw the completion of one of the biggest TLS scanning campaigns ever undertaken where 6 ha of Wytham Woods in Oxfordshire were scanned leaf-on and leaf-off. All this work contributes to a better understanding of the function of forests with respect to their ability to mitigate climate change.

Virtual Forests

As mentioned above, 3D data captured in the real world can be transformed into a forest of virtual trees. These can then be used in 3D radiative transfer models for a number of purposes.  For example, earlier this year Dr. William Woodgate from CSIRO visited the lab where his aim was to correct imagery captured with a high temporal and spatial resolution camera for differing illumination conditions.  To do this he used the librat, a Monte-Carlo ray tracing software package developed at UCL. For anyone interested in learning the basics of librat, there is a free course delivered using Jupyter notebooks for download.

Where are we off to next year?

Next year is looking like an exceptionally busy year for our team and instruments with scanning planned for Malaysian Borneo, Peru, Brazil and California as well as closer to home on the streets of Camden. We are particularly interested in combining scanning techniques over the next year, for example, combining mobile, terrestrial and airborne LiDAR to map the biomass of London’s street trees. Using the capabilities of the different sensors (e.g. rapid assessment of the ZEB-REVO, detailed volume estimates of the TLS and synoptic capture of airborne datasets), we aim to make the first detailed inventory of street tree biomass in London.

For those of you interested in a more frequent update on our activities, I would recommend following Mat Disney’s blog.