Automated lidar transmitter for multiparameter investigations within the Arctic atmosphere

The transmitter system of the ALOMAR Rayleigh/Mie/Raman lidar (RMR lidar), part of the ALOMAR facility at the island Andoya (69°N, 16°E) in Northern Norway, is presented. Long-term and multiparameter observations of the Arctic middle atmosphere on a climatological basis require a complex and automated transmitter system. To obtain winds using the Doppler method, two identical power systems driven by one single seeder system have been chosen. The seeder frequency is actively stabilized against an iodine absorption line with remaining fluctuations of less than 10^-8. Each power system can be used with its own steerable receiving telescope, moveable in elevation as well as azimuth. Using both systems in alternating operation on a pulse-by-pulse basis of the lasers, two wind components can be obtained simultaneously. Trends in the power laser beam positions are corrected by a direction control system leading to fixed axes of the laser beams before transmission into the atmosphere. The achieved beam pointing stability at the original beam diameter is better than ±20 μrad, which guarantees the beam to remain inside the very narrow field-of-view (FOV) of the receiving telescope and supports full daylight capability of the lidar. The whole transmitter system is controlled by computers, thus avoiding optical adjustments for months