CATS Cloud and Aerosol Data Products: New Features, Improvements, and Implications for the Future

The Cloud-Aerosol Transport System (CATS) is an elastic backscatter lidar that operated from the International Space Station (ISS) for 33 months (Feb. 2015 to Oct. 2017). The CATS processing algorithms leveraged the heritage of the CALIPSO algorithms and implemented lessons learned to create algorithms for two operating modes:

• Mode 7.1: multi-beam and multi-wavelength (532 and 1064 nm)
• Mode 7.2: single beam and single wavelength (1064 nm) operations

Additionally, simple near real time (data latency of <6 hours) CATS data products demonstrated improvements in aerosol and volcanic plume transport forecasts.

New CATS data products, the most accurate yet, will be released in late 2018 and show that many of the popular lidar data products (layer heights, backscatter, depolarization, cloud phase, aerosol type) can be accurately produced using a single wavelength lidar like CATS Mode 7.2. The major algorithm changes made in L1B Version 3-00 (V3-00) focused on the daytime backscatter calibration. Historical values for calibration from V2.08 were updated based on statistical comparisons with nighttime data. Nighttime CATS 1064 nm attenuated total backscatter (ATB), which is calibrated directly by normalizing to the Rayleigh profile, compares very well with CALIOP and ground-based Raman lidars.

Several changes were made in CATS L2O V3-00 data products to improve cloud and aerosol detection, as well as optical properties. The CATS L2O cloud-aerosol discrimination (CAD) algorithm was updated to improve the Feature Type Scores. The CAD algorithm now relies on 1064 nm perpendicular backscatter intensity, the fractions of clouds detected at 350 m (horizontal) for each 5 km profile, and advanced horizontal persistence tests for both night and day data. The results of these changes are more accurate discrimination of (1) low-level liquid water clouds vs. aerosols, especially over oceans and in the daytime data, (2) aerosol types based on better aerosol detection, and (3) upper troposphere/lower stratosphere (UTLS) aerosol vs optically thin cirrus. Additionally, constrained lidar ratio and extinction retrievals for above cloud aerosols (ACA) using the Hu et al. (2006) method have been added to the L2O V3 as standard products. CATS algorithms are very mature and demonstrate the utility of single wavelength space-based lidar products applications such as cloud diurnal variability, aerosol plume transport and forecasting, and ACA detection.