Mobile micro-pulse lidar measurement in Hong Kong

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.