Cloud remote sensing from space in the era of the A-Train

The notion of the A-Train constellation of satellites is described. This constellation includes five satellites with EOS Aqua and EOS Aura at each end of the constellation and another small satellite, PARASOL, carrying the POLDER polarimeter inserted in the formation between the larger EOS spacecraft. This constellation also includes the CloudSat and CALIPSO spacecraft that were inserted into the Aqua orbit on April 28th, 2006. This newly formed constellation, together with the earlier NASA TRMM mission, represent a new age of remote sensing of clouds and precipitation in that we are now able to combine the observations of active radar and laser systems with passive radiometric observations. This paper reviews a few selected but commonly used remote sensing approaches for observing clouds and precipitation and highlights the potential of the new observing capabilities of the A-Train. It is also highlighted how this new era provides us with the opportunity to move away from present artificial practices of 'observing' and analyzing clouds and precipitation as separate entities toward a more unified approach to observe clouds and precipitation properties jointly.