Development And Analysis Of Stratospheric Wind Lidar Receiver

Stratospheric wind measurement is important to research of solar-terrestrial physics, global climate and development of aerospace industry.Recently, University of Science and Technology of China developed a stratospheric wind lidar which has the ability to measure wind field from15to60km altitude. The lidar system consists of three direct-detection Doppler wind lidar based on molecular double-edge technique. One vertical lidar was designed to measure either vertical wind or atmospheric temperature profile. Line-of-sight wind speed measured by two inclined lidars could be used to calculate horizontal wind through vector composition. Except that the vertical lidar has an extra temperature-measurement module, the three lidars have the same structure, i.e. transmitter system, transceiver system, receiver system, and controlling system.Performance of a lidar was determined by its core part, which is receiver system. Based on the stratospheric wind lidar we deigned a fiber based lidar receiver. The receiver consists of a Fabry-Perot etalon, multimode fiber splitters, photo detectors, collimating lens and focusing lens. Parameter design and device selection of the receiver was discussed. Working processing of the receiver was given according to molecular double-edge technique.A locking channel for lock outgoing laser on the Fabry-Perot etalon was used in the stratospheric wind lidar. Lock was realized by calculating transmission of the outgoing laser on the etalon and made feedback adjustment on etalon cavity length. Accuracy of lock was mainly affected by calculation of transmission. As the outgoing laser has a pulse width of about6ns, sampling number was very few. To increase sampling numberin a pulse and therefore obtain more data on the pulse, anintegrating sphere of200mm diameter was introduced into the locking channel to extend the pulse to about13ns. More sampling number could be achieved under the same sampling rate. The accuracy of lock was therefore improved.In order to increase integration and stability of the receiver, multimode fiber splitters were introduced into the lidar receivers to substitute normally used discrete components like prism or beam splitter. Splitting ratios of splitters were found to be sensitive to luminance heterogeneity of the incident laser, therefore the lidar requires uniform incident laser, especially in locking channel. The integrating sphere in locking channel could randomize the laser luminance before the laser was emitted into the fiber splitter and guarantee the receiver’s stability.Calibration of the receiver channel was implemented by measuring splitting ratios of the splitters. Experiments that could scan transmission curves of the receiver were designed based on the receiver structure. Transmission curves were scanned and showed good agreement with the theoretical curves.The transmission curves also showed good stability under multiple scan, have a maximum relative standard error less than6%. Stratospheric wind lidar receiver performed better than mobile Rayleigh Doppler wind lidar receiver (designed by University of Science and Technology of Chinaearlier) in long-term stability.The receiver was applied in the lidar system. During field operation and contrast experiment in year2013and2014, lidar data was in good agreement with data from sounding balloon and European Centre for Medium-Range Weather Forecasts.Quasi-Zero Wind Layer, which had been observed by the mobile Rayleigh Doppler lidar in Xinjiang during summer of year2011, was shown. Benefit from high spatial and temporal resolution of the lidar data, the variation trend of the bottom and ceiling height of Quasi-Zero Wind Layer was analyzed. The phenomenon that thickness of Quasi-Zero Wind Layer has a trend of "increase-stable-decrease" at night was shown and one possible explanation was proposed.