Measurements of plant stress in response to CO2 using a three-CCD imager
Rouse, Joshua Hatley.
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In response to the increasing atmospheric concentration of greenhouse gasses, such as CO2 produced by burning fossil fuels, which is very likely linked to climate change, the Zero Emissions Research Technology (ZERT) program has been researching the viability of underground sequestration of CO2. This group's research ranges from modeling underground sequestration wells to detection of leaks at test sites. One of these test sites is located just west of Montana State University in Bozeman, MT, at 45.66°N 111.08°W. At this site experiments were conducted to assess the viability of using multispectral imaging to detect plant stress as a surrogate for detecting a CO2 leak. A Geospatial Systems MS3100 multispectral imager, implemented in color-infrared mode, was used to image the plants in three spectral bands. Radiometric calibration of the output of the imager, a digital number (DN), to a reflectance was achieved using a grey card and spectralon reflectance panels. To analyze plant stress we used time series comparisons of the bands and the Normalized Difference Vegetation Index (NDVI), computed from the red and near-infrared band reflectances. Results were compared with rainfall, soil moisture, and CO2 flux data. The experiment was repeated two years in a row; the first from June 21, 2007 to August 1, 2007 and the second from June 16, 2008 to August 22, 2008. Data from the first experiment showed that plants directly over the leak were negatively affected quickly, while plants far from the pipe were affected positively. Data from the second experiment showed that the net effect of leaking CO2 depends on the relationship between CO2 sink-source balance and vegetation density. Also, due to the strong calibration techniques employed in 2008, the imaging system was able to see the effects of water and hail on the vegetation. We have also found a way to image continuously through the day, not having to worry about clouds or sun-to-scene/scene-to-imager angle effects. This system's easy setup, automation, all-day imaging capability, and possibility for low cost makes it a very practical tool for plant stress measurements for the purpose of detecting leaking CO2.