With the school year beginning we have new instructors spinning up courses around the classroom logger we released in 2019.  Some of them are more focused on biology than we are so we did some noodling around to come up with a biophysical monitoring idea that could be done just about anywhere with as few resources as possible.

https://thecavepearlproject.org/2019/08/30/creating-a-normalized-vegetation-index-sensor-with-two-leds/

The result was a ‘Leaf Transmittance Index’ based on readings from an IR LED and the red channel of the indicator LED already on the logger. Although using garden variety LED’s with no real spec introduced several non-optimal aspects wrt frequency & bandwidth, the trial successfully distinguished ‘healthy’ vs ‘unhealthy’ plant leaves where a simple visual inspection could not.  Now, before all the bio folks jump on us for all the hand-wavy hacks, and creating a pseudo NDVI with transmittance, rather than reflectance: keep in mind this was meant from the start to be a conceptual proof of concept, rather than a rigorous tool. From a teaching point of view, students would have to create "custom calibrations" for their one-of-a-kind builds & for each plant species - but that's actually a useful teaching exercise in itself.