NASA takes the A-Train on Earth Day
A line of satellites follow each other in orbit, passing over at about 1:30 pm local solar time each day. This afternoon constellation of Earth observing satellites, nicknamed A-Train for the Aqua and Aura missions that that began it, work together to provide comprehensive global observations of our home planet.
Each mission is operating more than a decade beyond its designed lifetime.
This unique orbit allows nearly simultaneous views of the land, ocean, and column of atmosphere by multiple missions. It also began a bit by accident, in the early days of planning the Aqua and Aura missions.
In working around limitations in data transmission rates between the two satellites, scientists noted that resulting 15 minute spacing enabled Aura's Microwave Limb Sounder (MLS) instrument to look horizontally through the same portion of atmosphere Aqua's downward facing instruments are seeing.
Combining data from the specialized instruments on these satellites enables scientists to gain a better understanding of changing conditions which impact our weather and climate.
Meet the A-Train
The Orbiting Carbon Observatory 2 (OCO-2) leads off the A-Train with three high resolution spectrometers measuring CO2 concentrations regionally and globally.
Next comes Global Change Observation Mission-Water (GCOM-W1), a partnership with the Japan Aerospace Exploration Agency (JAXA). This mission looks at water vapor amounts and wind velocity above the ocean, along with sea water temperatures to better understand changes in the water cycle.
A minute or so behind is Aqua, the original member of the A-Train, launched in 2002. Aqua gathers nearly 90Gb of data each day about water in all its forms. Liquid in the oceans and lakes, solid in sea ice, as well as water vapor in the atmosphere.
Aura provides the "caboose" to the A-Train with study the chemistry of the atmosphere and its impact on air quality and linkage to climate change.
Combined together, the data provides researchers valuable information on the how the oceans, land, and atmosphere interact and change over short and long periods of time. This improves our understanding of climate change and improve weather forecasting.
There is a bit of a gap between Aqua and Aura, where PARASOL flew from 2004 until mission end in 2013. PARASOL was a French mission which studied the structure of clouds by looking at how light is reflected by aerosols, tiny droplets of water and ice that make up clouds.
Other trains in the sky
The train concept was extended in 2006 with the launch of the C-Train, flying in a synchronized orbit about 10 miles below the A-train. The trains meet up about every 20-days for combined observations across the whole fleet.
The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), a joint U.S./French collaboration that also looks at aerosols using a laser, leads off the C-Train. Data from this mission helps researchers understand the structure of clouds, especially when combined with visible light images from weather satellites like those you see each day from WRAL meteorologists.
The C-trains caboose is CloudSat, a joint U.S./Canadian mission which provides global survey of clouds which has provided improvements to atmospheric models used in predicting the weather over shorter periods and climate over much longer periods.
Timing CloudSat's orbit was particularly tricky because it has to avoid sunlight reflected off the ocean's surface directly back into the satellite's cameras and other instruments, known as sun-glint.
The lower altitude also puts about twice as much drag on the C-Train making the job of keeping them flying in formation a lot tougher.
The AM-Train, crosses the equator each morning around 10:30 am local solar time. Led off by Terra the flagship mission of the Earth Observing System with its five instruments that observe Earth’s atmosphere, ocean, land, snow and ice, and energy budget.
Terra is followed by Landsat, a joint NASA program with the US Geologic Survey (USGS) which has been monitoring changes in the landscape from space since 1972.
The images on the 70-foot sphere at the North Carolina Museum of Natural Sciences in Raleigh come from Landsat.
At that scale, the orbit would be about 4 feet above the brushed aluminum surface. But don't look for a model of the satellite that provided those images. At that scale it would be about the size of a human red blood cell.
