1. RECONFIGURATION of the RECEIVER SYSTEM for SODIUM DOPPLER WIND/TEMPERATURE LIDAR Vardan Semerjyan, Undergraduate Researcher Tao Yuan, Faculty Mentor The newly established USU Na Lidar has the capability to measure neutral temperature and horizontal winds in the mesopause region (80-110 km in altitude) under clear sky condition in full diurnal cycle. Current system setup allows the observations of zonal (east-west) and meridional (north-south) winds, but lacks the coverage of the wind speed in zenith direction, which is essential to estimate the vertical wind perturbations. Since such perturbations are most likely associated with the atmospheric gravity waves (bouncy waves) breaking events and the related energy, momentum transfer, this upgrade of the Na Lidar system will provide further detailed information to the ongoing studies of such gravity wave dynamics and the induced atmospheric instabilities in the MLT (mesosphere and lower thermosphere) region. The proposed addition of the fourth channel and the associated new design of the Lidar receiving system will not only enable the data acquisition of the zenith channel but, the same time, will produce a more compact and robust structure than the current design. The new design will accommodate four high quantum efficiency (40%) Hamamatsu PMTs in the Lidar receiver, therefore, increase the system signal/noise(S/N) ratio by a factor of two. The new design of the Lidar receiving system is more compact and robust structure than the current design and enables the data acquisition of the fourth zenith channel. It will accommodate high efficient Hamamatsu PMTs and will increase the system signal/noise ratio by a factor of two. Integrate new receiver system with the existing USU Lidar System Upgrade the signal acquisition program and hardware to allow acquiring signals from four separate channels Convert master control signal (master clock) coming from the optical chopper to 100 Hz Substitute electronic control of the USU Lidar with control software implemented in Labview Abstract The Na Lidar is an ideal instrument for Mesosphere and Lower Thermosphere (MLT) dynamics research due to its capability to provide high temporal and spatial resolution measurements of temperature and winds, etc. The Na Lidar takes advantage of the naturally occurring atomic sodium in the upper atmosphere, which can be used as tracers for Na resonance fluorescence Lidar to determine temperatures and winds [She and Krueger, 2007]. Harrell, S. D., Chiao-Yao She, Tao Yuan, David A. Krueger, J.M.C. Plane, Tom Slanger (2010) “ The Faraday Filter-Based Spectrometer for observing sodium nightglow and studying atomic molecular oxygen associated with the sodium chemistry in the mesopause region. "Journal of Atmospheric and Solar-Terrestrial Physics She C.-Y., and D. A. Krueger “Laser-Induced Fluorescence: Spectroscopy in the Sky” Optics & Photonic News (OPN), 35-41, September, 2007. Acknowledgement: Special thanks to Terry Zollinger for doing machining work To learn more about USU Lidar facility visit http://www.usu.edu/crrl/ The new receiver system consist of the following units, mounted together on single mounting plate. 1.Hamamatsu H7421PMTs (four) 2.Faraday filters(two) 3.Mechanical beam chopper (340D4 of SciTech Instrument) 4.Chopper blade 5.Collimating lens mounts(four) 6.Fiber optic cable connecters (four) 7.Lens tubes 8.Lens tubes for nighttime observation Figure 8. Na Lidar temperature measurement from UT day 220 to day 225 in 2011 Figure 7. Old Chopper System Figure 4. Mechanical design of new receiver system in Solid Edge ST Figure 2. Running the beams Figure 1. Lidar observation Figure 2. Lidar Receiver Sytsem Two 76 cm Newtonian Starsplitter II telescopes and one 35 cm Schmitt Cassegrain Celestron C-14 telescope used to collect backscattered light Figure 5. Faraday filter (exploded view ) Abstract Introduction Redesign of Receiver System Motivation Although the atmosphere is relatively stable in the vertical direction with average vertical wind speed in the order of a few cm/s, it can experience large perturbations (tens of m/s) in the short time scale that are mostly likely induced by wave breaking events. The proposed addition of the fourth channel, which will be assigned to the fourth zenith pointing Lidar beam, and the associated new design of the Lidar receiving system, will allow the Lidar’s measurement of such large vertical wind perturbations. Figure 3. Lidar Transmitter System CW Nd:YAG Laser CW Ring Dye Laser Pulsed Nd:YAG Laser Pulsed Dye Amplifier Doppler-Free Spectroscope Acoustic Optic Modulator Iodinefilter based Chirp Monitor Figure 6. Built Receiver System During night time observations, the assembly of filters and tubes is moved to the position where received light passes through the four optical tubes. During day time the assembly changes the position that let the two Faraday filters [Harrell et al., 2010] slide into the beam path and block the other two channels the same time. One of the many challenges is the positions of the four channels has to be aligned with great precision so that the chopper can open and close the four channels simultaneously. This is critical for the Lidar operation to block the strong echo below 5 km altitude but also let the useful return signal pass through. Lidar Observations Conclusion and Future Work References Currently USU Sodium Lidar is capable of simultaneously measuring temperature, zonal and meridional winds within mesopause region over full diurnal-cycles under clear sky condition. It started its regular observation of MLT region at USU since September 2010. This system operates at three different frequencies near the Sodium D2 line, and is currently using three-beam setup (West, East and North Beams) to measure LOS wind and temperature profiles of each Lidar beam. The LOS winds are then converted to horizontal wind base on the zenith angles.