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EEcology


Friday, August 15, 2014, by Bruce McAlister
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I am not a scientist; I am an engineer.

. . . Which makes my employment at an ecological research station a little odd. However, it is perfectly natural to have engineers here, it turns out - as long as you don't have too many. Scientists need specialized tools for research. Engineers are just the right people to create these tools. And so, here I am - building research equipment for scientists. Yes, I know; it doesn't get much cooler than that.

My project looks at how reflected light from the canopy -  which can show what the leaves are doing - changes throughout both the day and the year. I am not collecting data on the light values though; I am building a platform for data collection.

[The Harvard Forest tram]The Harvard Forest tram (my project) is an autonomous robot that travels between towers on cables above the forest canopy, taking measurements of the incoming and leaf-reflected light every few meters. The sensors that the tram carries are NDVI sensors, PRI sensors, a four channel net radiometer, a camera, an ultrasonic distance sensor, an infrared thermometer and a hyperspectral camera. These sensors show the activity of the leaves by measuring how how much light they reflect in particular wavelengths.

We are not the first to do these kinds of measurements at the Forest. Sensors mounted above the canopy on stationary towers can collect enough data to show daily and seasonal variations in the light reflectance, but they can only measure these values for the few trees directly underneath them. We can also measure many trees along a transect by hand, but because measuring by hand takes so much time we only see variations at the seasonal level.

The first prototype of the tram was constructed last summer by three Harvard Forest REUs. Their design used many of the same components that we are using now. This prototype was different, however, in that the tram car used wires to receive power and communicate with the control tower. In the second phase, the control computer was moved from the tram car to the tower and the tram computer was added to create a wireless communication link between the tower and the car.

The focus of the third phase of the project is to finish a prototype for long-term field testing. Our goal is to have the tram operating at its field location soon. This summer we have been adapting the hardware and software to operate in the Prospect Hill clear cut tract at the Forest. This exposed location will require the tram to be resistant to sun, wind, rain, snow and ice. The location is remote enough that repairs can be inconvenient and maintenance should be needed as little as possible.

[The three phases of the tram project; first, second, and third from left to right]

To design for these conditions, we've kept our hardware as simple and easy to repair as possible. Much of my focus this summer has been on eliminating unnecessary parts, simplify overly complicated systems, and strengthen weak components. For example, the previous system for stopping the tram car in the exact same spot in its dock every time used switches that sent a stop signal through four different computers before it reached the motor. This meant that the tram would not stop immediately when the switch contacted the dock. To make this better I connected the switches directly to the motor controller, with some fancy electrical magic and a capacitor in between of course, and now the motor stops immediately when the switch is depressed. To weatherproof the switch mechanism, I replaced the unsealed switch with a magnetic reed switch that I placed in a plastic jacket (that's my generic name for a Sharpie pen that I gutted) and mounted a magnet on the tram to trip the switch at the dock.

The tram has not been moved to its field site yet. On the Monday of the last week as we were prepping the tram to go out, our motor controller mysteriously stopped working. It's probably only coincidental that we had a thunderstorm the night before . . . Anyhow, our motor controller got a nice vacation back to Japan for repairs and we worked as best we could without a mobile tram.

A lesson I've been learning this summer, and am still learning, is that I need to plan for projects to not go as planned. I often find myself thinking that, "next time, when things don't go wrong, this will be much quicker." But I am realizing that things will always be going wrong in some respect and I just need to plan extra time and resources for these failures. Human optimism also makes me underestimate the time a task will take. According to Lau's Conjecture, human optimism should be accounted for by tripling the estimated time to accomplish a task. My work has been proving that this conjecture is accurate. I have lost the illusion that someday my work will go as planned within the time I imagine it to take. If it does go as planned I will be pleasantly surprised, but I am prepared for work to take thrice as long as I wish it would.

If you, dear reader, ever have the chance to be a Harvard Forest REU, do it! There is no substitute for this experience. Though there are many other places and experiences I love, there is nothing else I would rather have done this summer than be an REU here. I would attempt to describe to you the evenings by the campfire, the excellent food, the singing of songs and making merry after work that fill our lives with joy, but that would be akin to trying to whistle architecture or sculpt the scent of strawberry shortcake. If given the opportunity, I am convinced that you also will find that there is no substitute for experiencing the Harvard Forest REU program. 

Comments

Very cool project! Thanks for sharing!

Christopher
www.gunandcamera.com

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