Multi-wavelength light-emitting diode light source radar system and near-ground atmospheric aerosol detection

Near-ground atmospheric aerosol has a direct effect on the living and production of human, and the research on its detection attracts substantial attention from engineers and scholars in the community of environment. Traditional monitoring instruments can accurately and continuously detect the aerosols above the ground, but it is difficult for them to obtain the information about vertical distribution of near-ground aerosols. As is well known, lidar can act as an efficient method to detect the aerosol's temporal and spatial distribution. However, this technique is restricted in the potential applications of the detection of aerosol at a certain wavelengths or near range. That is because it usually presents fixed wavelengths and a large blind area. In this work, a new multi-wavelength light-emitting diode (LED) light source radar system is designed and established for detecting the characteristics of atmospheric aerosol near ground. The paper is outlined as follows. Firstly, the composition and working principle of the LED light source radar system are introduced. Based on the structure of radar's transmitter and receiver, the geometric overlap factor is analyzed and calculated. The minimum detection height of the LED light source radar system is then determined to be 60 m. Secondly, the inversion method for the echo signal of LED light source radar is studied. In consideration of the suitability of near-range detection of LED light source radar, the Fernald forward integration method is used for inversing the aerosol extinction coefficient. The calibration value of aerosol extinction coefficient is further determined with the ground visibility data. Finally, by using the designed multi-wavelength LED light source radar system (475 nm, 530 nm, and 625 nm), near-ground aerosol observation at night in Xi'an city is carried out and three atmospheric conditions including light, moderate and severe pollution days are considered. The height distribution curves of atmospheric aerosol extinction coefficient of three wavelengths within a height of nearly 300 m are obtained. The characteristics of the distribution and change of near ground aerosols are accordingly discussed. The experimental results show that the multi-wavelength LED light source radar provides an efficient implementation for detecting the vertical distribution of atmospheric aerosol near the ground, and can make up for the inadequacy of lidar in near range detection.