Autocollimation-Based Roll Angle Sensor Using a Modified Right-Angle Prism for Large Range Measurements.

An autocollimator is a popular angle measuring apparatus which lacks the capability to measure the roll angle. This paper proposes a novel roll angle sensor with a large measuring range that is based on the autocollimation principle. A modified right-angle prism (MRP) functions as a reflector to admit a collimated beam and return two outgoing beams to the sensor head.

Drizzle microphysical property and vertical air motions retrieval using Doppler lidar and radar measurements.

The microphysical changes in cloud formation and development are closely related to the vertical air motions. It is difficult to simultaneously detect microphysical parameters of drizzle and vertical air motions. This study proposes a method for the drizzle microphysical property and vertical air motions retrieval using Doppler lidar and radar measurements.

Orthogonal retrieval algorithm of atmospheric temperature profiles from pure rotational Raman lidar signals.

Aimed at the stability of calibration coefficients in a general non-orthogonal retrieval algorithm (NRA) of pure rotational Raman lidars (PRRLs), an orthogonal retrieval algorithm (ORA) of atmospheric temperature profiles based on the orthogonal basis function is proposed. This algorithm eliminates the correlation between the calibration coefficients in the NRA to reduce the influence of the number of calibration points and the selection scheme on the calibration coefficients. In this paper, the stabilities of calibration coefficients in the NRA and ORA are compared and analyzed, and the data analysis for atmospheric temperature profiles with a time resolution of minute-level are given, based on the developed Cloud Precipitation Potential Evaluation (CPPV) lidar data and the parallel radiosonde temperature data.

Correction method for temperature measurements inside clouds using rotational Raman lidar.

Rotational Raman lidar is an important technique for detecting atmospheric temperature. However, in cloud regions with strong elastic scattering conditions, elastic scattering crosstalk (ESC) is prevalent due to insufficient out-of-band suppression of the optical filter, resulting significant deviations in temperature retrieval. To address this challenge, a temperature correction technique for optically-thin clouds based on the backscatter ratio is proposed.

Optimized method for simultaneous detection of fog/aerosol particle size distribution.

We propose forward/lateral scattering of dual-wavelength (ultraviolet and short-wave near-infrared bands) radiation to simultaneously detect aerosol particles and fog droplet size distribution in an open atmosphere. The size distributions were described using a gamma distribution. A light-scattering detection system was optimized and designed, and the final wavelengths and scattering angles of ∼ 350 nm and ∼ 1100 nm, and 1°, 2°, 12°, and 35°, respectively, were selected.

Error simulation of atmospheric scattered radiance and its influence on slant visibility based on the SBDART model and Monte Carlo method.

Atmospheric scattered radiance is an important factor affecting slant visibility measurement in the daytime. This paper explores atmospheric scattered radiance errors and their influence on slant visibility measurements. Considering the difficulty in error synthesis of the radiative transfer equation, an error simulation scheme based on the Monte Carlo method is proposed.

Temperature measurement of cloud or haze layers based on Raman rotational and vibrational spectra.

Pure rotational Raman lidar is often used for atmospheric temperature profile measurements. However, high elastic scattering suppression ratios (>10) are required for temperature measurement in clouds and haze, which imposes stringent requirements on spectral separation techniques. To solve this problem, a lidar measurement technique based on vibrational and rotational Raman spectra is proposed.

Measurement method for slant visibility with slant path scattered radiance correction by lidar and the SBDART model.

Different from the existing methods for estimating averaged slant visibility by lidar and the traditional Koschmieder visibility formula, a measurement method for slant visibility is fundamentally proposed in this paper that considers the correction of slant path scattered radiance. Lidar is adopted to provide aerosol parameters, including optical depth and scattering parameters, and the SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model is used to solve the radiative transfer equation to obtain the corresponding radiance distribution; thus, the corrected apparent brightness contrast between the object and background along the slant path is used to achieve accurate slant visibility. Based on the measurement principle of slant visibility, a theoretical simulation and an analysis of the slant path scattered radiance are performed, and the resulting slant visibility is studied in detail in this paper.

Improved algorithm of aerosol particle size distribution based on remote sensing data.

The optical parameters (extinction or backscatter coefficients) of multi-wavelength beams can be used for the retrieval of the aerosol particle size distribution (APSD). An improved algorithm for APSD and aerosol microphysical parameters (AMPs) is studied and discussed by using only multi-wavelength extinction coefficients data. The regularized algorithm and prior value are combined for the retrieval of APSD and AMPs.

Optimized retrieval method for atmospheric temperature profiling based on rotational Raman lidar.

Aimed at addressing the disadvantages of restricted retrieval height caused by signal-to-noise ratio (SNR) differences between high-quantum-number and low-quantum-number pure rotational Raman scattering signals (PRRSs) obtained with the traditional retrieval method, an optimized retrieval method is proposed for atmospheric temperature profiling based on rotational Raman lidar. This method allows independent alternating solutions to high- and low-quantum-number PRRSs, where high-quantum-number PRRS lidar returns are used to solve the channel constant, and low-quantum-number PRRS returns with a high SNR are used for retrieving temperature profiles. The system sensitivity, SNR, and statistical error in temperature measurements by the two methods are first simulated and discussed, and the results are then compared to show that a higher SNR and stable sensitivity can be attributed to stable statistical errors with the optimized method.

Precise size distribution measurement of aerosol particles and fog droplets in the open atmosphere.

A precise measurement for the aerosol particle size distribution and fog droplet size distribution simultaneously in the open atmosphere is proposed. The extinction coefficient and small-angle forward scattering measurement are integrated into the detection for particle size distribution in the open atmosphere, and can achieve the fine detection of the particles in the atmosphere with radius between 0.1 to 30 μm.

Research on an adaptive filter for the Mie lidar signal.

The statistical properties of the noise in the Mie lidar signal are analyzed by the statistical hypotheses testing method. Based on this, an adaptive filter is proposed to eliminate the noise. The least mean square error algorithm is used to achieve optimal filtering, in which the mean square error is minimized by adjusting the filter's weight matrix.

Variations in the water vapor distribution and the associated effects on fog and haze events over Xi'an based on Raman lidar data and back trajectories.

A combination of more than two years of water vapor lidar data with back trajectory analysis using the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model was used to study the long-range transport of air masses and the water vapor distribution characteristics and variations over Xi'an, China (34.233° N, 108.911° E), which is a typical city in Northwest China.

Optimization design of spectral discriminator for high-spectral-resolution lidar based on error analysis.

Accurate aerosol optical properties could be obtained via the high spectral resolution lidar (HSRL) technique, which employs a narrow spectral filter to suppress the Rayleigh or Mie scattering in lidar return signals. The ability of the filter to suppress Rayleigh or Mie scattering is critical for HSRL. Meanwhile, it is impossible to increase the rejection of the filter without limitation.

Correction technology of a polarization lidar with a complex optical system.

A complex optical system used in polarization lidars often modifies the input polarization of the return signal so that it may significantly impact depolarization estimates and introduce errors to polarization lidar measurements. In most cases, retardation, depolarization, and misalignment of the system exist at the same time and interact with each other. Polarization effects of the system cannot be represented by a simple correction coefficient, so they cannot be removed using a traditional calibration method.