The A-Train platforms and their instrument manifests, described below, work together to produce a comprehensive picture of the Earth system. Most are passive instruments that detect radiation emitted or reflected from a target. Each instrument detects radiation in one or more spectral bands—a range of microwave, infrared, visible, or ultraviolet wavelengths. Some bands are relatively broad (as for imaging instruments), while others are extremely narrow (as for several thermal infrared-detecting instruments). The instruments cover a variety of different viewing angles and polarizations that allow light from specific directions and orientations, respectively, to be measured.
In contrast, CloudSat’s radar and CALIPSO’s lidar are active instruments that emit an energy pulse (microwave and visible radiation, respectively) and measure the energy reflected or backscattered to the sensor. Scientists study these return pulses and use them to create three-dimensional profiles of clouds and aerosols.