GOME-2 helps NASA study plant health
Data from the GOME-2 (The Global Ozone Monitoring Experiment–2) instruments on the Metop satellites are being used by NASA scientists to measure the health of plants.
The condition of a plant’s cellular structure, and, therefore, its health, can be measured by how much photosynthesis takes place. Photosynthesis is the process by which plants use the energy from sunlight to produce food.
During photosynthesis healthy plants re-emit some of the light as a faint, but measurable, glow. The greater the glow, the healthier the plant is. Low or no fluorescence can mean that the plant is stressed or shutting down.
That glow is invisible to the naked eye, but is detectable by satellites. Researchers from NASA, plus universities and research organisations in America and Germany, have discovered that the fluorescent glow from plants is being detected by the GOME-2 optical spectrometer.
Since the fluorescence signal is so weak very accurate radiation measurements, at high spectral resolution, are needed. With a good signal-to-noise ratio GOME-2 meets all these needs — using a wavelength region from 240 to 790 nm, using more than 4000 channels (Fig. 1 below). Fluorescence is most active from 650–800 nm and the research currently only uses wavelengths between 715 and 785 nm.
To distinguish the weak fluorescence signal from other very strong signals, like surface reflectivity and aerosols, the scientists use absorption lines in the spectrum of the sun (known as Fraunhofer lines).
Ruediger Lang, Remote Sensing Expert at EUMETSAT, said: "We are providing high spectral resolution radiance measurements in the near-infra red region, needed in order to observe such a chlorophyll fluorescence signal. GOME-2 is perfect for observing chlorophyll signals since it covers the spectral regions most sensitive to vegetation — the green part of the light spectrum — plus the near infrared part, which is used by the scientists."
Data from GOME-2 has enabled the scientists to produce maps with a 16 times increase in spatial resolution and a three times increase in temporal resolution over the first proof-of-concept maps released in 2011 from a different satellite instrument. Figure 2 (below) shows global distribution map of the fluorescence radiance signal as observed by GOME-2 in December 2009.
In their paper, Global monitoring of terrestrial chlorophyll fluorescence from moderate spectral resolution near-infrared satellite measurements: methodology, simulations, and application to GOME-2 , Joanna Joiner, from the NASA Goddard Space Flight Center and her colleagues, state: "Globally mapped retrievals are of high interest because they can provide information on the functional status of vegetation. Measurements of terrestrial chlorophyll fluorescence are directly related to photosynthetic function and are potentially useful for forest and agricultural applications, as well as assessment of the terrestrial carbon budget, including gross primary productivity."
Plants are vital to Earth and changes in their growing patterns and cellular conditions can be indications of changes in the climate. Researchers at Princeton University found that land ecosystems have kept the Earth cooler by absorbing billions of tons of carbon, especially during the past 60 years.
GOME-2’s prime role is to provide a detailed picture of the total atmospheric content of ozone and the vertical ozone profile in the atmosphere. In addition, the instrument provides information on a large number of additional trace gases related to the production and the destruction of ozone in the stratosphere and in the troposphere.
The GOME-2 instrument also monitors the level of air-pollution at a global scale by monitoring the concentration of nitrogen dioxide and sulphur dioxide from industrial emission. GOME-2 is able to monitor volcanic eruptions and the presence of aerosols, small particles in the atmosphere originating either from natural or industrial sources.
The global total column water vapour content measured by GOME-2 is very well-suited for use in climate monitoring, since atmospheric water vapour (H2O) is the most important natural greenhouse gas, accounting for about two-thirds of the natural greenhouse effect.