A Compact Rayleigh Autonomous Lidar (CORAL) for the middleatmosphere
Bernd Kaifler, Natalie Kaifler
Abstract
Abstract. The Compact Rayleigh Autonomous Lidar (CORAL) is the first fully autonomous middle atmosphere lidar system to provide density and temperature profiles from 15 km to approximately 90 km altitude. From October 2019 to October 2020 CORAL acquired temperature profiles on 243 out of the 365 nights (66 %) above Rio Grande, southern Argentina, a cadence which is 3–8 times larger as compared to conventional human operated lidars. The result is an unprecedented data set with measurements on two out of three nights on average and high temporal (20 min) and vertical (900 m) resolution. First studies using CORAL data show for example the evolution of a strong atmospheric gravity wave event and its impact on the stratospheric circulation. We describe the instrument and its novel software which enables automatic and unattended observations over periods of more than a year. A frequency-doubled diode-pumped pulsed Nd:YAG laser is used as light source and backscattered photons are detected using three elastic channels (532 nm wavelength) and one Raman channel (608 nm wavelength). Automatic tracking of the laser beam is realized by implementation of the conical scan (conscan) method. The CORAL software detects blue sky conditions and makes the decision to start the instrument based on local meteorological measurements, detection of stars in all-sky images, and analysis of ECMWF weather forecasts. After the instrument is up and running, the strength of the lidar return signal is used as additional information to assess sky conditions. Safety features in the software allow operation of the lidar even in marginal weather which is a prerequisite to achieving the very high observation cadence.