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In February, 2005, Lauri attended a Measuring Vegetation Health (MVH) workshop at the Lawrence Hall of Science in Berkeley. On the third day, attendees were encouraged to create their own project using MVH concepts and tools that they could use in their science center.
One of the aspects that is so exciting about Lauri's project is that by photographing this time series of leaves as one image, the lighting for all leaves was constant. This allowed for rapid comparison of the leaves using MVH software. Also, Lauri pulled from the plant shortly before the photograph, which minimized any drying effects on the leaves.
The activity below has been adapted for DigitalImageBasics software.
The leaves on a single branch are of a range of ages. Some have just opened, others are mature and fully photosynthesizing, and others appear to be past their productive stages and will be discarded by the plant. Can we see differences in the light reflected from these leaves of different ages?
Below is a color photograph of the leaves on a branch or stem of a Nasturtium, a flowering plant. The newly opened leaf is on the left, and each leaf to the right being older than the one on the right. The oldest leaf is on the far right.
Using the DigitalImageBasics software, the red, green, and blue layers of the Nasturtium photograph are displayed separately (the darker the color represents little of that color being reflected from the surface of the leaf; the brighter the color, the greater reflectance of the color from the leaf):
Use AnalyzingDigialImages to compare the layers of colors within the color photograph. The formula is (Intensity A - Intensity B) / (Intensity A + Intensity B).
The color of the greater value is displayed:
This formula tends to minimize difference in illumination caused by shadows and uneven surfaces (such as crinkly or curled leaves).
Red versus Green (normalized). Except for dying leaves, plant leaves reflect more green light than red light.
Green versus Blue (normalized). Similar to above, plant leaves reflect more green light than red light.
Red versus Blue (normalized). The newly opened leaf (far right) has noticeably greater red light being reflected compared to blue light. The mature leaves that are photosynthesizing best are either equally reflective in red and blue light or there is more blue light being reflected. As the leaf ages beyond this point, greater and greater red light is reflected from the leaf.
Based on this image, research is being conducted at the University of New Hampshire to correlate these red vs blue values to the amount of chlorophyll in leaves. Results and conclusions of this work will be posted when completed.
This image was taken indoors, near a window, during a rainy day. Under the conditions, this is an outstanding photograph!
Using DigitalImageBasics software, the different layers of the visible and infrared photographs were separated and saved as separate images (one for near infrared, one for red, and one for green). Using the SatImageMaker software, the layers were brought together to make an image that would be taken with the Landsat sensor and displayed in one of the most common color schemes (infrared displayed as red, reflected red light displayed as green, and reflected green light displayed as blue light). For more information, see the guide "Calculate Normalized Difference Vegetation Index (NDVI) from Merged Visible and Infrared Digital Photos"
Would the purple filter that is used as a plant stress detection device work with the Nasturtiums? What is your decision?
Use AnalyzingDigitalImages software to measure the length, wide, and area of these leaves to see if the dimensions change as the leaves progress through their stages.
Repeat Lauri's work with plants in your garden, yard, or park. Please be responsible if using plants in parks – do not destroy the plant, especially rare ones!