The Afternoon or "A-Train" satellite constellation presently consists of five satellites orbiting in formation around the globe (Aqua, CloudSat, CALIPSO, PARASOL and Aura satellites).
Two additional satellites, OCO and Glory, will join the constellation by mid 2009. Each satellite within the A-Train has unique measurement capabilities that greatly complement each other. Many of the A-Train instruments view large swaths of the Earth at different wavelengths from the near ultraviolet to the far infrared. These sensors can detect clouds in a variety of sizes and shapes and can monitor changes in atmospheric composition.
They also observe temperature, relative humidity and the amount of sunlight refl ected back to space from the Earth. However, most of these instruments are able to view only the tops of thick clouds or are unable to resolve multiple layers of thin clouds and layers of dust and smoke particles. This information is key for understanding how clouds and particles can affect climate and weather. A cloud profiling* radar on CloudSat and a lidar (laser-radar) on CALIPSO provide this missing information. For the first time, a global view, including polar regions, of the vertical structure of clouds is available, for both day and night, from the A-Train under a wide range of conditions.
The satellites in the A-Train pass a fi xed point with approximately 15 minutes between the leading and trailing spacecraft while traveling at over 7 km per second. CloudSat and CALIPSO are controlled to an even fi ner requirement, within 15 seconds of each other, so that both instrument suites view the same cloud scene at nearly the same moment. This capability of studying clouds with multiple sensors is crucial because clouds can change substantially in just a few minutes.
| < A high level of requirements |
|---|
