ABSTRACT
A detailed assessment is carried out in relation to the influence of the uncertainties associated with the input auxiliary atmospheric state parameters on retrieving aerosol optical properties from high-spectral-resolution lidar (HSRL) observations. The study starts from a review of the main spectral structure of the Rayleigh backscattering followed by evaluating the temperature effects on a backscattering cross section of atmospheric molecules based on numerical simulation. It shows that the transmittance of the background interference filter should be taken into account, depending on the full width at half maximum, although overall temperature dependence is negligible. Based on the Taylor expansion of the Tenti S6 model, the systematic errors arising from input temperature and pressure profiles are analyzed. It is demonstrated that the atmospheric pressure profiles have limited effects on the inversion results of aerosol optical parameters, as the atmospheric pressure is usually quite stable. The relative errors of the aerosol backscatter coefficient mainly stem from temperature profile errors and highly depend on the aerosol concentration. Quantitatively, the aerosol backscatter coefficient error could be larger than 5% with a 3 K deviation of temperature when the backscatter ratio is larger than 1.1. The accuracy of aerosol extinction coefficient retrieval is affected not only by the error in temperature, but also by the error in temperature lapse rate; the retrieval accuracy is more sensitive to the latter than the former. Further analysis based on the sounding temperature data shows that the variation of the temperature inversion layer during the night could induce a bias larger than 0.04 km-1 on the aerosol extinction coefficient retrieval. Therefore, the time resolution of temperature measurement from sounding balloons twice per day is too low to obtain an accurate retrieval of the aerosol optical properties from the HSRL.
ABSTRACT
A half-wave plate (HWP) is a critical component for calibrating the gain ratio in polarization lidars. In this paper, the effects of a nonideal HWP on the gain ratio calibration measurements are analyzed. We focus on the ±45° method and the multi-rotation HWP method, which are the two main approaches for calibrating the gain ratio. Specifically, we discuss the influences of a nonideal HWP from two scenarios: an HWP with nonideal polarization properties and an ideal HWP under nonideal external conditions. The allowable ranges of relevant parameters for the nonideal polarization properties of HWPs are obtained, which can help to determine qualified HWPs in polarization lidars. Several external conditions, including ambient temperature variations, wavelength differences, and the tilt angles of HWPs, are also analyzed in detail. To the best of our knowledge, this paper represents the first comprehensive study on the effects of nonideal HWPs on the gain ratio calibration measurements, offering some guidelines on choosing a qualified HWP for proper use in polarization lidars.
ABSTRACT
A kind of intermittent pneumatic compression (IPC) apparatus is developed to prevent deep vein thrombosis (DVT),which is based on the theory of occurrence and prevention of the DVT and AT89C52 micro-controller. This paper introduces its principle, composition of electromechanical system and the software design. The apparatus has showed its characteristics of easy operation, high intelligence and high reliability.
