Free-space optical communication has long been a focus of the aerospace industry as it promises fast and secure transmission of data between the ground, airplanes and satellites. The transmission of the beam through free space – hence the name – is contemporarily the weakest point of this technology: It is sensitive to aerosols in the atmosphere. Reuniwatt is proud to be part of a project aiming to improve and predict the best availability of optical connections.
The technology of free-space optical communications is based on the transport of data by light (laser) and capable of multiplying the rate of data exchanges, enabling 10 to 100 times more data to be transmitted from space to the ground than would be possible using radio frequency systems. The transmission of the beam through free space is contemporarily the weakest point of this technology: Aerosols in the atmosphere can result in the scattering of the light and create echoes, and atmospheric turbulence can result in sudden drops of signal. As an expert for cloud observation and forecasting, Reuniwatt has joined the consortium of ESA-funded research project ANAtOLIA to characterize and monitor the availability of optical links across a variety of atmospheric conditions (Atmospheric moNitoring to Assess the availability of Optical LInks through the Atmosphere).
Atmospheric monitoring for the Optical Ground Stations
ANAtOLIA is a 4-year research project funded by ESA (2 million euros). The project aims to enable the continuous recording of local information on clouds, aerosols and atmospheric turbulence conditions for a period of two years and correlate them with other available data sources (meteorological sites, satellites, etc.). The project consortium members CNRS, Observatoire de la Côte d’Azur, Univesité Côte d’Azur, UMR Lagrange, Icare/Aeris, Norway University, Aibus DS, Thales Alenia Space, Latmos, Cimel and Reuniwatt will improve the knowledge of the availability of the optical link for the selected locations of the optical ground stations and validate in the long term the methods for predicting the availability of optical connections.
Overcoming cloud cover, aerosols and turbulence
Reuniwatt will provide a number of infrared sky imagers Sky InSight™ at selected sites, which allow the project team to acquire and process images of the entire cloud ceiling day and night thanks to an wide-angle infrared thermal camera system (8-13 µm): Clouds can be detected and their motion forecasted with high precision. ith Thicker clouds have a high optical depth and behave as nearly ideal blackbodies, while emission from thinner clouds depends strongly on their lower optical depth. The sky cameras help to classify cloud characteristics from radiance measurement. Amongst other tasks, Sky InSight™ will support the projects aim to identify the critical atmospheric transmission parameters and help with the monitoring equipment selection.
Infrared sky imagers play an essential role in measuring the cloud cover’s spatial and temporal distribution and give a feedback on its optical effects related to free-space optical communication links. Reuniwatt is proud to be on board this exciting project and contribute to the atmospheric characterization of worldwide locations for future optical ground stations. These locations will be tested for their properties to identify the least exposed to the alteration of optical transmissions by the clouds, aerosols and turbulence in the atmosphere.