5:15 PM - 6:45 PM
[PEM15-P09] Experimental evaluations on high-speed laser beam line switching for time-delayed multi-beam Na lidar observations at Tromsø, Norway
Keywords:Na lidar, Technical development, Multi-beam observation, Tromsø
Na layers play an important role in lidar observations of the upper atmosphere. The height coverage of Na lidars depends on the distribution of Na, which had been considered to be around 80-110 km heights. On the other hand, recent observations revealed Na distributions at higher heights (up to around 170 km), which are so-called thermospheric Na.
The Tromsø Na lidar is a system capable of simultaneous multi-beam observations in five directions. The lidar system was developed in 2009-2010, and at that time the thermospheric Na had not been known. Therefore, the Tromsø Na lidar was designed for Na at 80-110 km, and its inter-pulse period (IPP) in the pulsed laser is 1 ms, corresponding to a height coverage of 0-150 km. So, an extension of the height coverage is needed for observations of thermospheric Na by the Tromsø Na lidar.
In this study, we propose a method to extend the height coverage of the Tromsø-Na lidar, which is the time-delayed multi-beam method. In this method, we perform a pulse-to-pulse switching in the direction of the laser beam in the multi-beam lidar observations. If we apply this method to the two-direction observations of the Tromsø Na lidar, the IPP in each direction becomes 2 ms, which corresponds to the height coverage of 0-300 km.
To investigate the feasibility of this pulse-to-pulse switching, we have performed experimental evaluations on high-speed laser beam line switching using a commercial galvanometer scanner. In the experiments, the galvanometer scanner was operated at every 1 ms, which is the same as the laser repetition period of the Tromsø Na lidar system, and the laser beam line was switched in two directions. The two beam lines were measured from the point of view of the switching time and the pointing accuracy. As a result, the switching time was approximately 0.91 ms. Then, the pointing accuracy was approximately 0.17 mrad. In the presentation, we will show these experimental results, and discuss the feasibility of the time-delayed multi-beam method in the Tromsø Na lidar by considering its required performance.
The Tromsø Na lidar is a system capable of simultaneous multi-beam observations in five directions. The lidar system was developed in 2009-2010, and at that time the thermospheric Na had not been known. Therefore, the Tromsø Na lidar was designed for Na at 80-110 km, and its inter-pulse period (IPP) in the pulsed laser is 1 ms, corresponding to a height coverage of 0-150 km. So, an extension of the height coverage is needed for observations of thermospheric Na by the Tromsø Na lidar.
In this study, we propose a method to extend the height coverage of the Tromsø-Na lidar, which is the time-delayed multi-beam method. In this method, we perform a pulse-to-pulse switching in the direction of the laser beam in the multi-beam lidar observations. If we apply this method to the two-direction observations of the Tromsø Na lidar, the IPP in each direction becomes 2 ms, which corresponds to the height coverage of 0-300 km.
To investigate the feasibility of this pulse-to-pulse switching, we have performed experimental evaluations on high-speed laser beam line switching using a commercial galvanometer scanner. In the experiments, the galvanometer scanner was operated at every 1 ms, which is the same as the laser repetition period of the Tromsø Na lidar system, and the laser beam line was switched in two directions. The two beam lines were measured from the point of view of the switching time and the pointing accuracy. As a result, the switching time was approximately 0.91 ms. Then, the pointing accuracy was approximately 0.17 mrad. In the presentation, we will show these experimental results, and discuss the feasibility of the time-delayed multi-beam method in the Tromsø Na lidar by considering its required performance.