Wide-Field Infrared Survey Explorer (WISE) is a satellite launched in December 2009, aimed at a 1 year mission. The aim was to image the whole sky in Infrared (IR), aiming to observe stellar nurseries and to detect Asteroids. A reason to use infrared is that it penetrates Cosmic Dust.
It surveyed four Wavelengths in the infrared bands:
Differences in these, e.g., w1-w2 and w2-w3 are useful in identifying obscured Active Galactic Nuclei (AGN).
Wide Field Infrared Explorer (WIRE)