February 1, 2013

NASA Airborne Science Missions measuring pollutants from the ground up

An extensive program, aiming to correlate air pollution measurements by satellites, high and low altitude aircraft and ground stations is underway in southern California.

A similar extensive set of measurements have already been done over Baltimore, Md., and in the coming months, similar studies will be made in the Houston Texas area, and in Colorado.

The program is called DISCOVER-AQ, and its apt name stands for Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality. The program funding estimate is $30 million for the five year-long effort, which includes the four field investigations and data analysis

Over the next two months, measurements will be made using instruments carried by the NASA P-3B and B-200 aircraft. The ER-2 will carry aloft a set of three polarimeters. Also, a Gulfstream-III [GIII] aircraft will make measurements using a new radar to determine soil moisture. These flights are all based at the Dryden Aircraft Operations Facility at Air Force Plant 42 in Palmdale, Calif. These measurements will be correlated to those made by the afternoon constellation [the A-Train] satellites which pass over the study area at 1:30 p.m. each day. The Aqua and Aura spacecraft in particular will allow scientist to compare ground and aircraft data.


P-3B, B-200

The P-3B carries 8 instruments. These measure aerosols, nitrogen oxides, particulates, water, formaldehyde, ozone, carbon dioxide, and non-methane hydrocarbons. The B-200 has two instruments. These measure aerosol profiles and column values of ozone, nitrogen dioxide, and formaldehyde.

Sampling will focus on agricultural and vehicle traffic areas extending from Bakersfield to Fresno and between Highways 5 and 99. The flight path passes over six ground measurement sites operated by the California Air Resources Board and the San Joaquin Valley Air Pollution Control District. P-3B will fly spiral flights over the ground stations. These flights will be from an altitude of 15,000 feet to as low as 1,000 feet. They will sample air along agricultural and traffic corridors at low altitudes between the ground stations. The smaller B200 King Air will collect data from as high as 26,000 feet. The plane’s instruments will look down at the surface, much like a satellite, and measure particulate and gaseous air pollution.

Researchers are working to improve the ability of satellites to consistently observe air quality in the lowest part of the atmosphere. If scientists could better observe pollution from space, they would be able to make better air quality forecasts and more accurately determine where pollution is coming from and why emissions vary.

A fundamental challenge for space-based instruments monitoring air quality is to distinguish between pollution high in the atmosphere and pollution near the surface where people live. DISCOVER-AQ will make measurements from aircraft in combination with ground-based monitoring sites to help scientists better understand how to observe ground-level pollution from space.

DISOVER-AQ is collecting data that will prepare us to make better observations from space, as well as determine the best mix of observations to have at the surface when we have new satellite instruments in orbit,” said James Crawford, the mission’s principal investigator at NASA’s Langley Research Center in Hampton, Va. “NASA is planning to launch that satellite instrument, called TEMPO, in 2017.”


ER-2 PODEX measurements

The ER-2 is the NASA version of the Lockheed U-2S high altitude platform. It usually flies its missions at 60,000 to 70,000 feet.

At these altitudes it is a good simulator for the view from a satellite. NASA Dryden pilot Stuart Broce explained that the aircraft cabin is only pressurized to about 38,000 ft. The pilot is always in a slack pressure suite during the flight.

ER-2 carries the Polarimeter Definition Experiment (PODEX) in test flights so that data fro the new polarimeters can be compared to other data gathered by DISCOVER-AQ. Three teams have each developed prototype instruments that constitute PODEX. The Research Scanning Polarimeter was developed by Brian Cairns, PI, Goddard Institute for Space Studies in New York. The PI for the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) is David Diner, of the Jet Propulsion Lab. The Passive Aerosol and Cloud Suite polarimeter was developed by J. Vanderlei Martins, of the University of Maryland Baltimore County.

Polarimeters detect the plane of vibration of the light waves that are detected. Incoming sunlight is unpolarized, which means that the planes of vibration of the light waves are randomly oriented. When the sunlight interacts with Earth’s atmosphere or surface, the light waves can vibrate in preferred orientations. For example, interaction with highly structured particles or objects – things like industrial soot particles, dust, vegetation, or ice crystals in a cloud – can dramatically change the polarization of reflected sunlight. By analyzing the polarized light, inferences can be made about the scattering source.


Gulfstream III measurements

The Airborne Microwave Observatory of Subcanopy and Subsurface [AirMOSS] instrument will be flown aboard the GIII aircraft. This instrument uses 70 cm wavelength radar to penetrate to about 1.2 m [4 ft] into the upper part of the soil below trees. It will yield information on soil moisture, which correlates with the exchange of carbon into and from the atmosphere. Several regions of typical forests will be studied.


Airborne Tropical Tropopause Experiment (ATTREX)

Another ambitious research program has been announced by the NASA Earth Sciences Division Airborne Science Program. The ATTREX mission uses a heavily instrumented Global Hawk aircraft, which will take off from and be operated by the Dryden Flight Research Center. The Global Hawk is able to make 30-hour flights.

Water vapor and ozone in the stratosphere can have a large impact on our planet’s climate. The processes that drive the rise and fall of these compounds, especially water vapor, are not well understood. This limits scientists’ ability to predict how these changes will influence global climate in the future. ATTREX will study moisture and chemical composition in the upper regions of the troposphere, the lowest layer of Earth’s atmosphere. The troposphere ranges from about 8 miles to 11 miles above Earth’s surface. As the point where water vapor, ozone and other gases enter the stratosphere, it controls the composition.

Studies have shown even small changes in stratospheric humidity may have significant climate impacts. Predictions of stratospheric humidity changes are uncertain because of gaps in the understanding of the physical processes occurring in the tropical tropopause layer. ATTREX will use the Global Hawk to carry instruments to sample the tropical tropopause near the equator off the coast of Central America.

“The ATTREX payload will provide unprecedented measurements of the tropical tropopause,” said Eric Jensen, ATTREX principal investigator at NASA’s Ames Research Center in Moffett Field, Calif. “This is our first opportunity to sample the tropopause region during winter in the northern hemisphere when the troposphere is coldest and extremely dry air enters the stratosphere.”

Led by Jensen and project manager Dave Jordan of Ames, ATTREX scientists installed 11 instruments in the Global Hawk. The instruments include remote sensors for measuring clouds, trace gases and temperatures above and below the aircraft, as well as instruments to measure water vapor, cloud properties, meteorological conditions, radiation fields and numerous trace gases around the aircraft. Engineering test flights conducted in 2011 ensured the aircraft and instruments operated well at the very cold temperatures encountered at high altitudes in the tropics, which can reach minus 115 degrees Fahrenheit.

Six science flights are planned by March 15. The ATTREX team also is planning remote deployments to Guam and Australia in 2014. Scientists hope to use the acquired data to improve global model predictions of stratospheric humidity and composition.

The ATTREX team consists of investigators from Ames and three other NASA facilities; the Langley Research Center in Hampton, Va., Goddard Space Flight Center in Greenbelt, Md., and Jet Propulsion Laboratory in Pasadena, Calif. The team also includes investigators from the National Oceanic and Atmospheric Administration, National Center for Atmospheric Research, academia, and private industry.

ATTREX is one of the first investigations in NASA’s new Venture-class series of low- to moderate-cost projects. The Earth Venture missions are part of NASA’s Earth System Science Pathfinder Program managed by Langley. These small, targeted science investigations complement NASA’s larger science research satellite missions.

The DISCOVER-AQ mission is a partnership with the National Oceanic and Atmospheric Administration, the U.S. Environmental Protection Agency, and University of California campus branches in Berkeley, Davis, Irvine, and Santa Barbara. Other partners in the California campaign include the National Center for Atmospheric Research; the University of Maryland in College Park and Baltimore County; University of Colorado, Boulder; Pennsylvania State University, State College; University of Innsbruck in Austria; and Millersville University, Millersville, Penn

DISCOVER-AQ is an Earth Venture mission, part of the Earth System Science Pathfinder program managed at Langley for the Earth Science Division of NASA’s Science Mission Directorate in Washington, D.C.


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