Extending space-based global lidar measurements: The Cloud-Aerosol Transport System (CATS)

NASA's A-Train satellites provide an unprecedented opportunity to address uncertainties in cloud and aerosol properties that limit our ability to accurately model the Earth's climate system and predict climate change. As part of the NASA A-Train, the Cloud-Aerosol Lidar Infrared Pathfinder Spaceborne Observations (CALIPSO) satellite provides global lidar measurements of cloud and aerosol properties. However the CALIOP lidar onboard CALIPSO has reached its eighth year of operation, well past its expected lifetime, and the ATLID lidar on EarthCARE is not expected to launch until 2017 or later.

The Cloud-Aerosol Transport System (CATS) is an elastic backscatter lidar with three wavelengths (1064, 532, 355 nm) and HSRL capability at 532 nm. CATS will operate in one of three main science modes. The first mode consists of a CALIPSO-like multi-beam mode for backscatter and depolarization measurements at 532 and 1064 nm wavelengths. The second and third modes will use a seeded, frequency-tripled laser for HSRL and 355 nm technology demostration. CATS, built at NASA Goddard Space Flight Center as a payload for the International Space Station (ISS), is set to launch in late 2014.

CATS will fill the gap in global lidar measurements between the CALIPSO and EarthCARE missions, continuing the CALIPSO aerosol and cloud vertical profile data record. CATS simulations suggest the signal-to-noise ratio (SNR) and minumim detectable backscatter at 532 nm will be better than CALIPSO during nighttime and very similar during daytime operation. A collaboration between the CATS and CALIPSO groups will ensure continuity between data products for application to global datasets. The ISS orbit provides more comprehensive coverage of the tropics and mid-latitudes than sun-synchronous orbiting sensors, with nearly a three day repeat cycle. Thus, science applications of CATS include cloud and aerosol climate studies, air quality monitoring, and smoke/volcanic plume tracking.