MLS (Microwave Limb Sounder)

MLS is the Microwave Limb Sounder flown on NASA's Aura mission ^[1][2]. It is a passive microwave limb-sounding radiometer and spectrometer that measures thermal emission from the atmospheric limb ^[1][3]. Unlike nadir-viewing optical trace-gas instruments, MLS looks forward from Aura at the limb and scans from the ground to about 90 km roughly every 25 seconds ^[2].

The instrument uses broad microwave and submillimetre bands at 118, 190, 240, and 640 GHz, plus a 2.5 THz channel ^[3]. Its products include vertical profiles of ozone and other trace species, plus temperature, pressure, and cloud ice information for stratospheric ozone, climate, and air-quality science ^[2][1]. Spatial resolution varies by retrieved product, with NASA Earthdata listing about 200 to 500 km horizontal resolution and about 3 km vertical resolution ^[1].

For buyers, MLS is relevant when vertical atmospheric structure matters more than horizontal imaging detail. Its limb-sounding geometry makes it useful for profile retrievals and upper-atmosphere chemistry studies, while its microwave measurement approach provides a different observing regime from ultraviolet-visible nadir spectrometers ^[1][3]. JPL developed, built, tested, and operates MLS on Aura ^[3]. Users comparing Aura payloads should treat MLS as a profile-oriented microwave sensor, complementary to nadir atmospheric chemistry instruments that deliver column or near-column products ^[2][1].