Guy Norris Edwards AFB and Palmdale, Calif

Remote-sensing satellites have become indispensable tools for weather forecasting and resource monitoring and, given the right set of instruments, researchers believe future spacecraft could also dramatically improve the understanding of climate change and air pollution.

That is the aim of Earth science researchers involved in three parallel missions underway at NASA's Dryden Flight Research Center. From that site an unprecedented fleet of test aircraft is fanning out to explore the atmosphere from as low as 100 ft. to the edge of the stratosphere. The missions, two over California and one over the Pacific Ocean, are focused on testing new or improved sensors as well as gathering atmospheric data that will help guide the final selection of systems for future satellites.

Two turboprop-powered aircraft, NASA's Lockheed P-3B and Beechcraft 200 King Air, are flying in a coordinated mission as part of the Discover-AQ campaign. Otherwise known as the Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality, the effort is aimed at improving the ability of satellites to consistently observe air quality in the lowest levels of the atmosphere. The goal is to collect data from a variety of altitudes, including measurements from ground-based monitoring sites, and compare them to help design space-based instruments which will be able to distinguish between pollution found high in the atmosphere and closer to ground level.

Based at Dryden Aircraft Operations Facility in Palmdale, the two aircraft will collect atmospheric data over the same locations but at different levels. The King Air, equipped with a high-spectral-research Lidar (light detection and ranging) and an airborne ultra-violet/visible spectrometer, will shadow the P-3B while maintaining 26,000 ft. Acting as a virtual geostationary satellite, the King Air will be “looking down, providing a column view on the P-3B, which is collecting data on the detailed structure underneath,” says Jim Crawford, the mission's principal investigator at NASA's Langley Research Center in Hampton, Va.

Bristling with eight key instruments, the P-3B will measure particles, ozone, carbon monoxide, carbon dioxide and nitrous oxides. “These are all the things that can be measured from space but in addition, it will also have sensors to look at the sources, processes and causes of pollution. So it will monitor methane, hydrocarbon species and their composition to see whether they are made up of things like black carbon, ammonium nitrate or sulfur and so on,” says Crawford.

The aircraft will sample the air over agricultural and vehicle traffic areas in California's Central Valley over sites extending from Bakersfield in the south to Fresno in the north. When the flights pass over six ground measurement sites operated by the California Air Resource Board and the San Joaquin Valley Air Pollution Control District, the P-3B will sample the column of air by spiraling down from 15,000 ft. to much lower altitudes below 1,000 ft. “We've got to go much lower here as we're seeing that the pollution is mostly contained in the bottom 2,000 ft.,” Crawford says. The sites are located close to small airports; by conducting missed approaches to these runways, NASA is able to take samples from altitudes as low as 100 ft.

The P-3B, normally based at NASA's Wallops Flight Facility in Virginia, and King Air will visit the same sites three times a day in the morning, at noon and in the late afternoon. Data will be compared with measurements taken by the “A-train,” or Afternoon Constellation, which is a fleet of orbiting satellites that pass over California daily every afternoon. “The A-Train satellites have been useful in giving us a broader view of air pollution than we've ever had before,” says Kenneth Pickering, Discover-AQ's project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. “Discover-AQ will help scientists interpret those data to improve air-quality analysis and regional air quality models.”