CORAL (compact Rayleigh autonomous lidar) is a lidar instrument specifically designed for the investigation of gravity waves in the middle atmosphere between 25 and 100 km altitude. The project’s uniqueness is its fully autonomous operation, i.e. the system controls and monitors itself without human support. For example, the software built into CORAL monitors the weather condition using cloud cameras, in-situ weather measurements and weather forecasts. Based on these input data, the software decides when to begin with lidar observations, and the lidar system is automatically started up.
Conversely, the lidar is stopped without human intervention in case clouds form above the lidar or when the sun rises above the horizon. This high level of automation is a first for mesospheric lidar systems. Since the run-time of the lidar is not limited anymore to working hours of an operator, observation hours can be drastically increased. For the first time, the large number of consecutive observations obtained by CORAL will allow statistical analysis of gravity wave parameters in the timeframe of single days to several months.
CORAL was first employed during the GW-LCYCLE2 campaign at the Geophysical Observatory in Sodankylä, Finland during winter 2015/2016. During six months, several hundred hours of high-resolution temperature data was obtained. Subsequently, CORAL was moved to the Sulzberg in the Bavarian Forest, Germany as part of the ARISE-2 programme of the European Union. Again, several hundred hours of data were recorded during five months, among them the detection of a noctilucent cloud which is very rare mid latitudes.
Back in Oberpfaffenhofen the instrument was extended in 2017. The temporal resolution was increased to 10 ms, additional channels were added, and the beam stabilization automated.