Hi all,
I need to measure the vertical profile (LAI at different heights) in a sparse and heterogeneous canopy. The canopy is around 10-15m tall and we do not have tall enough towers to get to the top of the canopy so measurements must be ground based.
Does anyone have any advice on the best way to do this? I have been reading a bit and it seems like some people are developing LiDAR techniques to estimate vertical profiles from the ground, but firstly I'm not sure if this technique is totally reliable yet so any input/opinions on this would be very helpful.
I am not sure if we can access to a LiDAR sensor. As an alternative, I've also read about hemispherical photography being used - does anyone know of this being used to estimate vertical profiles, or does this just get you a 'flat' LAI measure?
Thanks so much!
In a two-layered stand with two different species I used two different tripods for getting hemispherical photos. The smaller one to measure the LAI of the understory (pictures from 1m above the ground), and the big one was lifted over the understory (15 m high). The high tripod is very heavy and uncomfortable. You need at least one assistant. Perhaps this will help.
Pictures only from the ground will give just the total LAI for a defined radius, but not the distribution of leaves on a vertical gradient. It's also important for choosing the correct method, if you have one or more tree species. All optical methods are based on the assumption of homogenous monolayered stands with only one tree-species. Im also very interested in a solution for this problem.
Using hemi-photos at different height should give you some okay results. Make sure you use an inversion that consider foliage clumping.
As a comment to Sylvain... The Hermispherical photographs would need that you get the camera into the canopy.......
Terrestrial Lidar might work but it will not measure LAI but the surface areas of leaves, stems and branches (as does hemispherical photography), Also I am not sure if the algorithms are readily available......
Nay picture analysis needs calibration. You may attempt felling some tree and remove vegetation by height if the soil is flat. Then you may apply LAD to volumetric sections in m2 m-3. LAI is referred to soil surface but LAD varies with voxel position . refs in http://park.itc.u-tokyo.ac.jp/joho/Omasa/462.pdf
As Frank said, with hemispherical photographs, you would need to move the camera up through the canopy. At every level you would get the plant area index above the camera.
I have an algorithm for vertical plant area index retrieval using terrestrial LiDARs, but it's not published yet (only in a conference paper and my thesis in French). But it's far from being automated for easy use. I have been working on other stuff lately and haven't had time to finish and submit it (although I spent a lot of time on it lately). As for Guido comment, it's not that difficult to got from LAD to LAI.
https://www.researchgate.net/publication/315688737_Natural_Resource_Mapping_Using_Landsat_and_Lidar_towards_Identifying_Digital_Elevation_Digital_Surface_and_Canopy_Height_Models
Article Natural Resource Mapping Using Landsat and Lidar towards Ide...
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