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February 2000

MOPITT, launched at last, needs one more nudge

The MOPITT team awaits launch as they watch NASA TV from the Lazy Dog Saloon on 16 December. The launch ended up being postponed for two more days. (Photo by Carlye Calvin.)

NASA's Terra satellite blasts off from Vandenberg Air Force Base on 18 December.

It wasn't a football, but a satellite poised atop a long, slender rocket in the center of the big TV screen at the Lazy Dog Saloon on 16 December. About two dozen members of ACD's Measurements of Pollution in the Troposphere program gathered at the North Boulder sports bar late that Thursday morning, hoping to watch the launch of a NASA satellite with MOPITT and four other instruments on board. Software engineer Cheryl Craig arranged the launch party, complete with live satellite broadcast from California's Vandenberg Air Force Base by NASA TV.

The satellite had been scheduled for a summer 1998 launch and then delayed several times, so the mood at the Dog was both excited and cautious. "It's been a long time in coming and it feels good to be here at this point," said Cheryl, a veteran of several space-based instrument projects. "I remember when we were writing the proposal for this [in the spring of 1988]."

"I hope it doesn't blow up," said student intern Tom Lauren, a CU computer science major. It didn't blow, but the launch was scrubbed, despite Linda Henderson's crossed fingers and toes. The countdown halted for about 15 minutes when a superlight aircraft intruded on the rocket's airspace; then a problem with an automatic sensor emerged, and that was it for Thursday. There were a few sighs and moans, but the word came through that another attempt would be made on Friday, and the event segued seamlessly from launch to lunch.

Friday was no go as well, due to "launch ground system problems"--the sensor still wasn't fixed. It wasn't until just before noon MST on Saturday the 18th--in the final seconds of a 25-minute launch window--that the magic word liftoff was spoken and Terra, the flagship of NASA's Earth Observing System (EOS), took to the skies. Several people gathered in program head John Gille's office to watch the event on the Web (launch photos may be viewed at http://terra.nasa.gov/Events/launch_photos.html.)

The mission

MOPITT being eased into a vacuum chamber for testing. Data from this thermally controlled environment provided crucial prelaunch calibration information. (Photo courtesy NASA.)

MOPITT evolved out of conversations between James Drummond (University of Toronto) and John when Drummond was at NCAR on sabbatical in 1987. As John recalled for the UCAR Quarterly a decade later, "We talked about the coming EOS experiment, and I said, 'The world really needs a way to measure tropospheric CO [carbon monoxide].' " He suggested exploiting the correlation radiometry technique Drummond had been using for stratospheric measurements. To sense the lowest levels of the troposphere, Drummond developed a new device, MOPITT's length modulator; John did some calculations with Beiying Wu, a visitor from the Chinese Academy of Sciences, to demonstrate that the technique had the required sensitivity, and the two then determined the gas pressures required within the instrument.

John Gille. (Photo by Carlye Calvin.)

Drummond has overseen construction of MOPITT as a Canadian Space Agency experiment. Co-principal investigator John [Gille] heads the 20-person ACD team that developed the software to retrieve and process the data as an EOS-funded project. Jinxue Wang is co-investigator and MOPITT project leader. (For more on MOPITT's development and NCAR's participation in EOS, see the UCAR Quarterly.

The only chemistry instrument on Terra, MOPITT is designed to make long-term global observations of CO and methane in the lower atmosphere. In addition to those trace gases, Terra will simultaneously study clouds, water vapor, aerosols, and land-surface and ocean properties, as well as the interactions among them and their effect on the earth's energy budget and climate.

Somewhere between two and five billion tons of CO enter the atmosphere each year as a byproduct of fossil fuel combustion and biomass burning and through natural emissions from plants. Natural and human-related emissions appear to be roughly equal. Aircraft- and ground-based instruments have provided a patchwork of measurements in space and time, but the complete picture has eluded scientists thus far.

"MOPITT will give us a chance to watch carbon monoxide plume by plume, day by day, as it rises above major source fires in Africa, South America, and Indonesia and wafts over the oceans toward other continents," says John. As the data analysis becomes more sensitive, it should reveal CO emissions from heavily polluted cities as well.

Near the earth's surface, CO is a deadly poison when highly concentrated. As it rises into the atmosphere, it is converted into carbon dioxide by taking oxygen atoms from molecules of the hydroxyl radical (OH), the elusive but powerful agent that cleanses the atmosphere of pollutants. Because of its high reactivity, short lifetime, and low concentration, OH can't be measured from space, but monitoring CO will open the window to understanding the cleansing processes and their implications for pollution levels.

Carbon monoxide is also an excellent tracer for observing global transport in the troposphere. Its lifetime of two months is long enough for the gas to be tracked as it rises from the surface and journeys around the globe, yet short enough to prevent it from mixing evenly in the atmosphere, which would obscure its sources and paths.

MOPITT will determine CO concentrations at four levels in the lower atmosphere. Its resolution is 22 kilometers horizontally and 3 km vertically (13.6 and 1.8 miles, respectively).

"Because pollutants can travel long distances, there's no truly pristine area left on earth, not as we once imagined," says John. "Tracking CO from space is a key to observing how pollution from one continent can reach and adversely affect another, reminding us that we have the capacity to pollute the globe."

MOPITT will also measure methane, which rises into the air from far northern wetlands and subtropical rice paddies, as well as from cows, sheep, termites, natural gas leaks, and other sources. Methane--which, like carbon dioxide, is a greenhouse gas--has a lifetime of ten years. With plenty of time to mix evenly around the globe, its sources and tracks are difficult to unravel. Though there's only a half billion tons of it, the gas absorbs infrared radiation emitted by the earth 60 times more efficiently than carbon dioxide does. MOPITT is designed to observe the total vertical column of methane.

The long wait to launch Terra gave the team more time to develop better tools for data assimilation (the process of updating a model throughout its run with more and more observed data). MOPITT data will be assimilated into ACD's comprehensive atmospheric chemistry model, MOZART, to build a global picture of source regions and transport of CO as well as methane.

It's anticipated that MOPITT data will play a role in future field campaigns, including this year's Southern African Regional Science Initiative (SAFARI-2000); next year's Aerosol Characterization Experiment (ACE-Asia) and Transport and Atmospheric Chemistry near the Equator (TRACE-P) missions; and, in 2002, the Effects of Tropical Convection Experiment (ETCE) and NCAR's Megacity Impact on Regional and Global Environments-Mexico campaign. (Originally slated for this summer, MIRAGE-Mexico has been delayed due to budget constraints. For more on MIRAGE, see http://www.ucar.edu/communications/staffnotes/9904/aerosols.html.)

Are we there yet?

By mid-January, four weeks after liftoff, engineering reports from MOPITT and the other instruments aboard Terra looked good. But delays for the instrument were not yet over.

On 11 January Terra's flight computer aborted an orbit adjustment just one minute into the maneuver, when sensors detected a slight rolling motion in the spacecraft. Flight engineers want to lift Terra about 50 km (30 mi) higher, into orbit exactly 15 minutes behind Landsat, so that two surface-mapping instruments aboard the satellite can exploit their synergy with Landsat. After the 11 January shutdown, NASA engineers began analyzing the telemetry to come up with a new plan to safely position the spacecraft. As of 27 January, a new ascent-maneuver plan was approved prescribing a week-long series of short burns by the rocket thrusters, expected to culminate in final orbit on 12 February.

In the meantime, the door protecting MOPITT's sensitive optics from spent thruster fuel remains shut. "Everything's on hold," says MOPITT data manager Dan Ziskin, "but this is just buying us more time so that we're even more ready when the data start coming in." The team has been evaluating evaluating and tweaking the algorithms used to derive CO and methane amounts from the radiation detected by MOPITT. And with the first engineering data beaming down, they can test, adjust, and tune aspects of the data processing software. "It's a good time to check some of these things out," John says. After a decade of planning and 18 months of launch delays, he's willing to wait a few weeks.

Zhenya Gallon and Anatta

On the Web:
NCAR news release, 19 December 1999

Two ACD Web sites have more information and links to collaborators' sites:

http://www.acd.ucar.edu/projects/mop and

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Edited by Bob Henson, bhenson@ucar.edu
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