Dengxin Hua

Ultraviolet high-spectral-resolution Rayleigh-Mie lidar with a dual-pass Fabry-Perot etalon for measuring atmospheric temperature profiles of the troposphere

We report what is believed to be the first demonstration of measurement of tropospheric temperature profiles in daytime by use of a high-spectral-resolution Rayleigh-Mie lidar at an eye-safe wavelength of 355 nm. Atmospheric temperature is determined from the linewidth of the Rayleigh spectrum. Two Rayleigh signals are detected with Fabry-Perot etalon filters with a dual-pass optical layout. The Mie signal is detected with a third etalon filter for correcting the Mie component in the Rayleigh signals. The temperature statistical uncertainties are below 1 K up to a height of 3 km in nighttime and 2 km in daytime with a relatively compact system that uses laser energy of 180 mJ and a 25-cm telescope. Good agreement between lidar and radiosonde measurements is obtained.

Ultraviolet Rayleigh–Mie lidar with Mie-scattering correction by Fabry–Perot etalons for temperature profiling of the troposphere

A Rayleigh-Mie-scattering lidar system at an eye-safe 355-nm ultraviolet wavelength that is based on a high-spectral-resolution lidar technique is demonstrated for measuring the vertical temperature profile of the troposphere. Two Rayleigh signals, which determine the atmospheric temperature, are filtered with two Fabry-Perot etalon filters. The filters are located on the same side of the wings of the Rayleigh-scattering spectrum and are optically constructed with a dual-pass optical layout. This configuration achieves a high rejection rate for Mie scattering and reasonable transmission for Rayleigh scattering. The Mie signal is detected with a third Fabry-Perot etalon filter, which is centered at the laser frequency. The filter parameters were optimized by numerical calculation; the results showed a Mie rejection of approximately -45 dB, and Rayleigh transmittance greater than 1% could be achieved for the two Rayleigh channels. A Mie correction method is demonstrated that uses an independent measure of the aerosol scattering to correct the temperature measurements that have been influenced by the aerosols and clouds. Simulations and preliminary experiments have demonstrated that the performance of the dual-pass etalon and Mie correction method is highly effective in practical applications. Simulation results have shown that the temperature errors that are due to noise are less than 1 K up to a height of 4 km for daytime measurement for 300 W m(-2) sr(-1) microm(-1) sky brightness with a lidar system that uses 200 mJ of laser energy, a 3.5-min integration time, and a 25-cm telescope.

Ultraviolet Rayleigh–Mie lidar for daytime-temperature profiling of the troposphere

A UV Rayleigh-Mie scattering lidar has been developed for daytime measurement of temperature and aerosol optical properties in the troposphere. The transmitter is a narrowband, injection-seeded, pulsed, third-harmonic Nd:YAG laser at an eye-safe wavelength of 355 nm. Two Fabry-Perot etalons (FPEs) with a dual-pass optical layout filter the molecular Rayleigh scattering components spectrally for retrieval of the temperature and provide a high rejection rate for aerosol Mie scattering in excess of 43 dB. The Mie signal is filtered with a third FPE filter for direct profiling of aerosol optical properties. The Mie scattering component in the Rayleigh signals, which will have influence on temperature measurements, is corrected by using a measure of aerosol scattering because of the relative insufficiency of Mie rejection of Rayleigh filters in the presence of dense aerosols or clouds, and the Mie rejection capability of system is thus improved. A narrowband interference filter is incorporated with the FPEs to block solar radiation. Also, the small field of view (0.1 mrad) of the receiver and the UV wavelength used enhance the ability of the lidar to suppress the solar background signal in daytime measurement. The system is relatively compact, with a power-aperture product of 0.18 W m(-2), and has a high sensitivity to temperature change (0.62%/K). Lidar measurements taken under different weather conditions (winter and summer) are demonstrated. Good agreement between the lidar and the radiosonde measurements was obtained in terms of lapse rates and inversions. Statistical temperature errors of less than 1 K up to a height of 2 km are obtainable, with an averaging time of approximately 12 min for daytime measurements.

Daytime Temperature Profiling of Planetary Boundary Layer with Ultraviolet Rotational Raman Lidar

An ultraviolet rotational Raman lidar system has been developed for measuring the vertical temperature profile of the planetary boundary layer in the lower troposphere. Daytime observation was realized using the ultraviolet pulsed laser at a 355 nm wavelength with a 5 W average power, and reducing the field of view of the receiving optics. The system has relatively compact and eye safety features. A high-resolution grating is employed with narrow band interference filters to reject intense elastic Mie scattering noise mixed in the molecular Raman scattering signals. Calibration measurement was carried out with a radiosonde and the results showed good agreements. A statistical temperature error less than 1 K was obtained up to heights of 2.3 km for nighttime and 1.8 km for daytime measurements with a 4 min observation time.

UV Rayleigh–Mie Raman Lidar for Simultaneous Measurement of Atmospheric Temperature and Relative Humidity Profiles in the Troposphere

A Rayleigh–Mie Raman lidar system at a wavelength of 355 nm has been upgraded for simultaneous measurements of atmospheric temperature, relative humidity and aerosol profiles in the troposphere. Temperature is determined from the Rayleigh spectral linewidth. Water vapor is determined from the intensity of the water vapor vibration-Raman line centered at 407 nm. A high-resolution grating is used to separate the water vapor vibration-Raman line and Rayleigh–Mie scattering spectrally from the lidar returns. Two Fabry–Perot filters with a dual-pass optical layout are used to detect the temperature changes. The measurement shows that statistical temperature errors of less than 1 K are obtained up to a height of 3.5 km, and the uncertainties of the water vapor in relative humidity are less than 10% at a height of 2.5 km when using a lidar system with 200-mJ laser energy, a 25-cm-diameter telescope and 3.5-min observation time. The performance of the lidar system is evaluated by comparison with radiosonde measurements. Close agreements are obtained between the lidar and radiosonde measurements.

A Compact, Eye-Safe Lidar Based on Optical Parametric Oscillators for Remote Aerosol Sensing

A compact, high-sensitivity, eye-safe lidar system has been developed using an efficient KTP optical parametric oscillator (OPO) at the wavelength of 1.57 μm. Mie scattering intensities and depolarization ratios were detected for two-dimensional mapping of distribution of aerosol concentrations by rapid laser beam scanning. The system is useful and practical for sensing urban and industrial atmosphere.

Development of practical UV Rayleigh lidar for measuring atmospheric temperature profiles in the troposphere

A new Rayleigh scattering lidar system at eye-safe 355nm ultraviolet wavelength has been developed for measuring vertical profiles of atmospheric temperature in the lower troposphere, based on the high-spectral resolution lidar (HSRL) technique using two narrow-band Fabry-Perot filters. The Doppler broadened width of the Rayleigh backscatter signal was measured for the temperature analysis. The central frequency and the width of the two filters are carefully selected to optimize the detection sensitivity of the filter. In order to reject the intense Mie backscattering component introduced in the Rayleigh signal, which affects the temperature accuracy, the third narrow-band filter has been installed to measure the Mie scattering intensity. A signal processing method has been developed to derive the temperature profile. In a preliminary experiment, it was shown that the temperature sensitivity of the filter is 0.4%/K and the measurement error is about 1K at 2km height.

Observation and analysis of urban boundary layer characteristics with Raman-Mie lidar

Long-term observations of atmosphere aerosol optical properties over Xi’an area have been carried out by a Raman-Mie lidar and a Micro-pulsed 3D Scanning Mie lidar, which were built at Xi’an University of technology with the laser wavelength of 355nm and 532nm, respectively. The Raman-Mie lidar is used for observation of the atmospheric temperature, water vapor and aerosol profiles simultaneously. In order to deeply discuss the temporal-spatial evolution of the mixed-layer within the urban boundary layer (UBL), the method of combining the absolute minimum of first derivative and second derivative of the range-squared-corrected signal (RSCS) of lidar was used to retrieve the mixed-layer depth (MLD). By using continuous observations of 24-hour (THI display), the MLD in temporal and spatial variation are clearly revealed. Also, the results of continuous observations from July 2006 to October 2011 have been analyzed for revealing the seasonal cycle and the annual cycle of the MLD. By analyzing the average MLD, it is obviously shown that the MLD of seasonal cycle is higher in summer than in winter over Xi’an area. Otherwise, by investigating the relationship of atmospheric boundary layer height, relative humidity and temperature, and the dependence characteristics and a general disciplinarian between them are then obtained. The achievement is of great importance for studying the proliferation of urban pollution and obtaining a complete meteorological status of the urban atmosphere.