Research Method

Research Method

Our classes (ISD & MSSD) followed GLOBE's Green Down protocols for observing fall senescence in trees near our schools. Both used ALTA Spectrometers to measure reflectance for 9 wavelengths from specific leaves. MSSD observed a Silver Maple Oct. 21-Dec 2, 2002. ISD observed a Sugar Maple Oct 11-Nov 6, 2002. Students at both schools gathered environmental data (daily minimum/maximum temperatures, precipitation, cloud type and cover) using GLOBE's atmospheric protocols. We collaborated by following the same research questions, sharing web page reports, and discussions in videoconferences.

Since we wanted to know how leaves change during the fall, we decided to see if we could use leaf reflectance to measure the changes. We measured leaf reflectance using an ALTA Spectrometer (The Lunar and Planetary Institute). The ALTA is a device for measuring color proportions and light wavelengths from real world objects. The spectrometer uses seven visible colors and two invisible colors (infrared-1 and infrared-2).

(Graph from Introduction to Remote Sensing, Campbell 1996)

This graph shows how a leaf reflects light in the visible and near infrared spectrums. In class we used the ALTA to measure reflectance from green leaves in September and found that they showed very similar profiles, with low reflectance in the blue area, high reflectance of green light and a very high reflectance
for infrared light.

The diagram below helped us understand how the different wavelengths of light are reflected from a leaf. Based on this information we developed a hypothesis about how the reflectance measurements of the different wavelengths will change as the environmental factors changed.

(Picture from Introduction to Remote Sensing, Campbell 1996)

This picture shows red, green, blue, and infrared light interacting with a leaf.

At MSSD we visited and measured our marked leaves 3 times/week. We chose 4 leaves on a southern side of the tree. A permanent marker put dots on each leaf stem so we could find them again. We used ALTA Spectrometers to measure wavelengths absorbed and reflected from leaves. The ALTA has colored buttons that match lights underneath. A screen shows reflectance coming from the leaf. We pressed each button, which produced a wavelength, which bounced back from the leaf surface to the ALTA's electric eye. We made a light-blocker for covering the opening on the ALTA to prevent outside light from entering the electric eye. After measuring a white paper for a standard, we'd return to class and use an online calculator to get % reflectance. We wanted to do our research in a wooded area, but nothing is near MSSD. We did the measurements about 1130 EST. Other students visited the GLOBE weather-station daily and read the min/max thermometer, measured precipitation, and observed clouds. At ISD we used these same methods, but used black paper on a clipboard rather than a light-blocker. We recorded the data from 2 leaves, instead of 4, 2-3 times a week.

MSSD Students:

Reading the min/max thermometer