Last week, the NASA DC-8 flew three flights over the California Central Valley to test the performance of a laser-based instrument designed to measure methane in Earth’s atmosphere.   The Methane Sounder Instrument, built by Haris Riris and his team from the Goddard Space Flight Center, may one day map methane from a future Earth or Mars orbiting satellite.

On Earth, methane is an important greenhouse gas produced by certain types of bacteria in soils and in the digestive tracts of some animals. Large quantities of methane are also produced as a result of forest fires and human industrial processes.  Knowledge of the global distribution and abundance of methane is important for understanding global climate change. 

Methane has also been recently detected on Mars.  Because methane is rapidly destroyed in Mars’ atmosphere, it must have been produced relatively recently.  While geological processes can produce methane, another exciting possibility is that Mars’ methane is produced by life. Determining the abundance and locations of methane sources on Mars is therefore extremely important for understanding recent geological (and perhaps biological) processes occurring on the Red Planet.

Before instruments are installed on satellites or spacecraft, many are first tested from NASA airplanes.  The Methane Sounder instrument team spent two weeks at the Dryden Aircraft Operations Facility in Palmdale, CA installing and testing their instrument on the NASA DC-8.  They spent several days aligning and testing the instrument from the airplane on the ground before finally testing its performance on three flights over the California Central Valley.  

Methane Sounder instrument PI Haris Riris (left) and Stewart Wu (right) test the alignment of the laser underneath the DC-8 at the NASA Dryden Aircraft Operations Facility.  Before flying their instrument on the DC-8, they fired its laser from the parked airplane toward the ground, reflected the laser off of a mirror underneath the airplane (above), and aimed at a nearby building.  The infrared laser is invisible to the human eye.

Inside the DC-8, while parked at the Dryden Aircraft Operations Facility, Haris Riris (center) and Martha Dawsey (left) align the laser for the Methane Sounder instrument.  The laser is fired straight down through a port on the underside of the aircraft.  To test the alignment, it was reflected off of a mirror (see above) and then off of the side of a nearly building.

The Methane Sounder Instrument detects methane with an infrared laser beam.  The laser emits light at a wavelength (color) that is too red for the human eye to detect (1.65 microns).  This wavelength corresponds to one of the wavelengths that the methane molecule absorbs light.  As the laser passes through the atmosphere and bounces off of the ground, methane molecules in the atmosphere absorb some of the light from the laser.  Measuring the amount of absorption that occurs as the instrument passes over different locations allows the team to build methane maps.

Although current Earth-orbiting satellites have instruments that can detect and map Earth’s methane, the laser-based system of the Methane Sounder will enable much higher accuracy methane detections and higher resolution methane maps than are possible with current non-laser based instruments.  With some modifications, the laser system could also be used for a Mars-orbiting satellite.

The NASA DC-8 early morning before takeoff for the Methane Sounder Instrument test flight on August 24, 2011.

To test the instrument, the team flew at a variety of altitudes over a large methane source (a cattle feedlot) in the California Central Valley.  

Flight track (in red) for August 24, 2011.  The DC-8 took off from Palmdale, California, flew northwest to the California Central Valley and flew in a large racetrack pattern around a cattle feedlot.

Altitude profile of the DC-8 from August 24, 2011.  The DC-8 took off from Palmdale, flew at 10,000 feet toward the cattle feedlot and then increased in altitude in 5000-foot increments while flying in a racetrack pattern over the California Central Valley (see flight track map above).

Haris Riris (right) and his group from the Goddard Space Flight Center watch as they acquire data with the Methane Sounder Instrument onboard the NASA DC-8.

Cattle feedlot near Coalinga, Central California seen from 10,000 ft from the NASA DC-8.  Due to the large number of cattle concentrated in such a small area, this feedlot is a large methane source.

The instrument performed outstandingly well, detecting the presence of methane in the atmosphere at all altitudes. “The Methane Sounder is the first demonstration of methane detection using lasers from an aircraft flying above 30,000 ft," said Riris.  "It should be a valuable tool for monitoring greenhouse gas emissions, especially in the Arctic.” 

The Methane Sounder instrument team is all smiles in flight onboard the DC-8 as their instrument performs well.

Funding for the Methane Sounder was provided by the NASA Astrobiology Science and Technology for Instrument Development program with support from the ASCENDS CO2 Instrument Incubator Program.