An eye-safe, mobile micro-pulse Mie lidar system has been established at City University of Hong Kong since November 2002. The system is a co-axial setup with a diode pumped Nd:YAG laser source of 532nm. Since measurements in public areas are required, the system was designed to be eye-safe by operating at a few micro-Joules pulse energy and high repetition rates (1 to 4 kHz) and the beam diameter was expanded to about 3 inches. Since the lower atmosphere is of interest, a co-axial design setup was adopted for improved near range performance. The receiver is a 235mm diameter Schmidt-Cassegrain telescope with a variable iris diaphragm for adjustable field-of-view, allowing for optimal near range or far range measurements. A narrow bandwidth filter (0.3nm) is used to reduce the stron solar radiation. The system is housed in a small van for field measurements at various sites around Hong Kong. Data is inverted using Fernald's method to obtain extinction profiles. Aerosol loading and boundary layer height have been examined at several sites for each season of the year 2003. The boundary layer heights obtained from lidar data measured at City University of Hong Kong are compared with radiosonde data measured at the King's Park meteorological station of the Hong Kong Observatory. In addition, seasonal trends of the maximum mixing height (MMH) measured at City University will be discussed.
One year of continuous measurements of visibility, temperature and relative humidity at the Hong Kong International Airport at Chek Lap Kok (CLK) are combined with the concentrations of the respirable suspended particulates (RSP) measured in Tung Chung near the Airport to extract annual and seasonal characteristics of the aerosols. The knowledge of aerosol characteristics obtained is used in the development of inversion methods for aerosol extinction retrieval from Lidar data. In this paper, the details fo aerosol characteristics and retrieved aersosol extinction profiles are presented. This additional data product requires no additional hardware to the existing Lidar, but only additional computational research efforts. The knowledge of spatil aerosol distributions during haze episodes will be valuable to aviation meteorologists at Chek Lap Kok. Long term visibility studies using Lidar of this kind will help our understanding of the air pollution problem in a coastal urban city like Hong Kong.
In studies of the internal boundary layer, it is important to make the lidar both eye-safe and capable of measuring near range extinction to high accuracy. The inversion of data is much more challenging due to the weaker signal from an eye-safe lidar. The method of inversion employed in this paper is the Fernald's method. Because the digitization system is capable of obtaining returns in the time interval of a few seconds, formal statistical analysis and error propagation are introduced in the inversion. Different weighting schemes are used during the averaging of the inversion and the results from scattered cloud data as well as pure aerosol profiles will be discussed. Results from several sites and under different meteorological conditions will be reported.
An eye-safe, mobile micro-pulse Mie Lidar system has recently been integrated. The system is capable of taking slant angle 360 degree horizontal scans of aerosol distributions, as well as vertical boundary-layer profiles in a zenith pointing position. The Lidar is co-axial, and the transmitter is a high repetition rate, diode-pumped micro-joule pulse energy, Nd:YAG 532 nm laser. The receiver is a compact Schmidt-Cassegrain f/6.3 telescope. The whole system can be fitted into a small van for field observations. The main objective in building this Lidar in Hong Kong is for monitoring spatially varying aerosols and vertical distributions within the lower few km of the troposphere. In this paper, the near range corrections from geometric ray tracing are presented together with field data. Representative spatial scans over urban Hong Kong are also given. The new system will be deployed in the very near future to study the correlation between the spatial distribution of aerosols and local traffic conditions. The Lidar design may represent a typical commercial product of the current technology.