Aura

The atmosphere-monitoring satellite Aura joined a constellation of orbiting spacecraft known as the A-Train shortly after its launch from Vandenberg Air Force Base on July 15, 2004.
 
The A-Train is noted for its close formation flying in a polar orbit more than 400 miles above the Earth. Traveling at 15,000 miles per hour, this collection of spacecraft is barely 15 minutes apart from first to last. Within the cluster, CloudSat and CALIPSO in the middle are figuratively flying "wingtip-to-wingtip," only 15 seconds apart, with Aura being at the tail end.

The Earth Observing System

The Aura satellite is part of NASA's Earth Observing System (EOS). While a variety of spacecraft in various orbits make up the EOS, the A-Train spacecraft fly in a tight pack because they all monitor the atmosphere. By following so closely one after the other, they each make a wide array of different atmospheric measurements at virtually the same time and place over the Earth.

The intense stream of all types of data from the A-Train cluster enables scientists to not only observe and predict weather but also to study:

  • climate change
  • greenhouse gases
  • pollution
  • the ozone layer.

The Atmosphere's Contents

Aura's mission is to catalog the quantities and altitudes of a variety of pollutants, greenhouse gases and ozone in the troposphere and lower stratosphere, which includes the area from near the Earth's surface to 60 miles above it. The Aura also measures atmospheric temperatures and the water and ice content within clouds.
 
Orbiting the Earth 14.5 times a day, Aura and the other A-Train platforms deliver large quantities of data to NASA ground teams that distribute it to various scientific communities. These data help scientists:
  • evaluate pollution trends
  • measure the effects of global warming
  • monitor atmospheric health
  • predict critical changes in Earth's protective ozone layer.

The chemicals Aura can identify include:

  • carbon dioxide and carbon monoxide
  • chlorine and bromine compounds, including CFCs
  • hydrocarbons, hydrogen cyanide and formaldehyde
  • nitrogen compounds
  • oxygen, ozone and hydroxyl
  • particulates (smoke, dust, aerosols)
  • sulfur dioxide.

Aura's Advanced Instruments

Aura has four spectral imaging instruments that identify the signature electromagnetic emissions (or absorptions) associated with various energy waves, ranging from ultraviolet and visible light to infrared and microwave frequencies.
 
Each instrument uses a different technology, is sensitive to specific altitude ranges and focuses on certain sets of chemicals and atmospheric measurements. While some of the devices are forward looking, others face aft or point straight down. All of them are able to scan the same section of atmosphere within 13 minutes of one another.
 
The beauty of the mission design is that many of its specific measurements are made by more than one instrument, allowing data to be cross-checked and literally viewed from different perspectives.

Ozone Monitoring Instrument (OMI)

The most important instrument necessary to maintaining Aura's 34-year satellite observation of the atmosphere's ozone layer is the downward-pointing OMI that measures reflected light in a selected range of the visible and ultraviolet light spectrum. Its viewing range extends 1,500 miles from side to side.
 
Along with measuring features of the ozone, the OMI also gathers data about ultraviolet radiation (and particulates) while identifying trace gases contributing to ozone depletion. While its most important mission is to provide data on the health of the ozone layer, in January 2008, the OMI tracked a plume of sulfur dioxide from the eruption of Chile's Llaima volcano as it drifted eastward across the southern Atlantic Ocean.

Microwave Limb Sounder (MLS)

The forward-looking MLS detects the microwave emissions of trace gases implicated in the destruction of the ozone layer. Keep in mind that the term "Limb sounder" refers to scanners facing forward or aft toward the Earth's horizon.
 
MLS also provides researchers with the first global measurements of atmospheric hydroxyl and hydroperoxy radicals that contribute to ozone depletion. These measurements assist in determining the effectiveness of pollution controls while observing and predicting the health of the ozone layer.
 
The MLS' ability to also measure the water vapor, temperature and ice content of clouds gives scientists additional data for verifying climate change models.

Tropospheric Emissions Spectrometer (TES)

By scanning both downward and aft, the infrared imaging TES measures:
  • carbon monoxide
  • gases in the atmosphere
  • ozone
  • water.
By measuring from two angles, TES overcomes the difficulties in making such infrared measurements in the presence of clouds.
 
Although TES measurements focus on the lower ranges of the atmosphere (up to 20 miles), they do overlap with similar MLS and HIRDLS measurements in the mid to high regions of the atmosphere. When correlated with data from other instruments, TES verifies readings and highlights any critical aberrations.

High Resolution Dynamics Limb Sounder (HIRDLS)

HIRDLS, also an aft facing infrared scanner, is designed to scan both vertically and horizontally. Its cryogenically cooled detectors operating below the temperature of liquid nitrogen are able to capture weak differences in infrared signals, giving it a high-resolution capability.
 
Collecting information on a wide variety of trace gases, ozone, water and particulates, HIRDLS focuses on the middle to upper reaches of the atmosphere, providing additional confirmation and extension of overall mission data.
 
Resources
 
National Aeronautics and Space Administration (n.d.). Aura. Retrieved Feb 7, 2008, from the NASA Web site.
 
National Aeronautics and Space Administration (n.d.). Earth Observing System Aura. Retrieved Feb 7, 2008, from Goddard Space Center Web site.
 
National Aeronautics and Space Administration (n.d.). A-Train Constellation. Retrieved Feb 7, 2008, from the NASA Web site.