Saturday, 9 July 2016

Mondah plot snaps

Andy has been working through the Mondah data from the first two GEM plots, and here are some examples of what they look like. First up is a transect through the MNG-03 plot, which covers 1 full row of 100m, and is about 20m deep. The plot shows the scanner locations on the 10m grid along the bottom (3 rows of them). The colours represent points coming from different scanning locations, with each colour corresponding to the colour of the scan location 'dot' - it's quite hard to see those for any other than the nearest ones on the black background, but you get the idea. For example, the purple points in the upper part of the tall tree in the centre come from scans to the far left and right in this case, showing how scan locations far from a given tree can often reveal the most detail at the top, due to being able to see through the surrounding crowns more easily.
Transect through MNG-03 showing the points from 3 rows of scan locations. There are 121 locations in each plot in total i.e. 11 rows of 11 locations, starting at 0, 0 and moving up to 100, 100 in 10m spacing. The point cloud here is drastically reduced (by factor of 1000) to allow easier manipulation.
 The image below shows a fill resolution example of a typical large tree with very grand buttressed roots, in the centre of the MNG-04 plot. In this case the colours represent the reflectance (returned energy) of the points, so the reflectance of points from the nearby broad trunk and roots is very high (near white), while the reflectance from the leaves and from points further away is much lower (orange through to dark red and black).
Reflectance image of small section of MNG-04 plot. This shows the full point cloud density.
Meanwhile, some more results from the ZEB-Revo scan are shown below. First, a height map of the whole plot, which shows the ZEB sees around 30m in some cases. So we can see the lower parts of the trees well, up to the crowns of the taller trees, but no detail in the upper part of the canopy. There are ~130M points in the 1ha cloud in total. Note that the heights aren't relative to the ground level but to the total height variation across the cloud. So the highest points (upper right) are still only 20-30m above the ground, but are on a raised area and so 30-40m above the lowest points. So the red parts here are largely a map of underlying topography. 
ZEB-Revo scan of MNG-04 plot, with the colour representing height, from 0 (blue) to around 35-40m (red).
Another view of the ZEB scan of the plot, from above this time.
View from above, looking down on the ZEB-Revo scan of the MNG-04 plot.
And a zoom in on one section in the diagonal gap towards the left of the plot. This gap may not be real - I think it may be a function of my scanning pattern going haywire during my walk of the plot. Staying on the grid is hard when you're struggling to walk, not fall down the slope or large holes, trip over logs and vines and hold the scanner at the same time!
Zoom in of small section of the ZEB scan of the MNG-04 plot.