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DATE: 2022-03-15
AUTHOR: John L. Godlee
In the SECO Project[1] we want to monitor seasonal patterns of leaf production (phenology) of trees and understorey plants in savannas. Most of this work is being led by Patricia Morellato[2] and a post-doc, Desirée Ramos[3], both based in Brazil. They have been developing a system for monitoring leaf phenology using camera traps, the same kind that one would use to monitor animal activity. The camera traps are set to capture images every hour during daylight hours, facing towards either a grass sward or looking down over the top of a tree canopy. The images can then be analysed to ascertain how green the vegetation is. Using cameras to monitor phenology will help us to separate the phenological signal of the trees and the grasses, which is difficult to do using aerial or satellite imagery.
Up to now, the cameras have been mounted on large tower scaffold structures called flux towers[4], which measure atmospheric and weather conditions using various sensors. These towers are expensive to set up however, and are quite rare, especially in southern Africa where I work. I have been thinking about ways to attach the cameras to the upper branches of large trees, so that they can look down on the main canopy below at an oblique angle. I came up with a design for an adjustable tree-mounted support. The mount needs to be made of metal, as plastic will become brittle in the sun. The mount also needs to be very solid, as we aim to leave these cameras in place for a whole year.
Parts I used:
3x M10 washers, 30 mm external diameter
2x 1/4" UNC eye bolts, 120 mm shank length, 15 mm eye diameter
2x 1/4" UNC nuts
2x 1/4" washers, ~15 mm external diameter
1x M10 split-ring washer
1x M10 flanged head nuts
1x M10 set screw, 60 mm length
1x large worm clamp/hose clip
Note that the M10 bolts, nuts and washers were chosen because the M10 bolt fits through the eye of the eye bolts. This could be altered to a different size depending on availability and the particular eye bolts used. I chose a 60 mm long set screw because I wanted to be sure I had plenty of excess length, but in reality the length of the washer, eye bolt, head nut stack is only ~30 mm, so I could have got away with a 40 mm long set screw.
The eye bolts need to be 1/4" UNC thread. This is because the camera traps I am using, along with most other camera equipment, use that thread size to attach to tripods and other mounts.
The eye bolts are only 120 mm long because I couldn't find any shorter bolts with the correct thread size. In the UK at least, it's quite hard to find imperial threaded bolts. I will cut these bolts down to about 60 mm with a hacksaw, then re-thread the ends to get rid of any jagged edges.
The size of hose clamp needed will vary depending on the size of the tree branch where the camera is mounted. I chose clamps with diameters: 40-80 mm, 70-120 mm, 110-170 mm.
You will also need a power drill to drill a hole in the hose clamp to fit the end of the eye bolt through it.
The split ring washer helps to keep everything tight by creating friction between the flanged head nut and the first washer. I experimented with putting split ring washers between the eye bolts, but the washers I had were too small.
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