TWP Site Hosts Preliminary Study for Long Term Measurements of Greenhouse Gases

 
Published: 15 April 2006

To validate the space-based carbon dioxide retrievals by the Orbiting Carbon Observatory (OCO) through comparative carbon dioxide measurements, ARM’s Tropical Western Pacific site in Darwin, Australia, is hosting a ground-based solar-viewing Fourier transform spectrometer (FTS) mobile laboratory, sponsored by the OCO Science Team. Between January 15 and February 7, 2006, overflights of the FTS site, as well as “flights of opportunity” by ARM’s Proteus aircraft during the Tropical Warm Pool International Cloud Experiment, were completed. Additional flights from the European Union’s Geophysical aircraft over the site in November and December 2005 also provided measurements of FTS spectra and in situ carbon dioxide. These data are being analyzed, and will be validated against international standards prior to use in future related research.

A camera, weather station, and sun tracker/protective dome are located on the roof of the fully automated FTS mobile laboratory. Inside the shelter, the spectrometer receives the reflected solar beam from the sun tracker (inset), while the main computer system operates all the instruments and acquires the data.

Light from the sun is absorbed by different gases as it passes through the Earth’s atmosphere. Measurements of the solar spectrum at high resolution allow scientists to calculate the concentration of these gases in the atmosphere. In the FTS mobile laboratory configuration, a sun tracker sends a solar beam downward through a hole in the roof. This beam hits a mirror positioned at 45 degrees below the hole and is directed into the spectrometer. The FTS measures the spectrum of the sun in the near-infrared spectral region at very high resolution.

The OCO is a National Aeronautics and Space Administration (NASA) Earth System Science Pathfinder Project (ESSP) mission designed to make precise, time-dependent global measurements of atmospheric carbon dioxide from an Earth-orbiting satellite. After launch in 2008, scientists will analyze OCO and FTS data to improve our understanding of the natural processes and human activities that regulate the abundance and distribution of this important greenhouse gas. This improved understanding will enable more reliable forecasts of future changes in the abundance and distribution of carbon dioxide in the atmosphere, and the effect that these changes may have on the Earth’s climate.

In November 2005, ARM operations personnel at the Darwin site assisted with installation of the FTS operations shelter, equipment, power, air conditioning, and communication links. Another FTS will be installed and validated at ARM’s Southern Great Plains site, after side-by-side testing with the OCO flight instrument has been completed. Long term operation of both FTS mobile labs at these two ARM sites will continue through the end of the OCO mission (2010).