Andrew Y. S. Cheng

Internal boundary layer structure under sea-breeze conditions in Hong Kong

Abstract A three-dimensional atmospheric model is used for modelling the airflow pattern and internal boundary layer (IBL) development over the Hong Kong region that comprises hilly terrain and complex coastline. Observations used to verify the model are drawn from 32 meteorological stations and a ground-based lidar system. It is found that the modelled results are in good agreement with the observed airflow field and IBL development. Due to the interaction of complex terrain and sea-breeze circulations, several confluence zones of wind fields are found in different locations, depending on the background wind velocity and the differential-heating rate between land and sea. Subsequently, these kinds of wind field patterns give rise to a three-dimensional dome-shaped IBL distribution that forms an impediment to air-pollutant dispersion outside of the layer.

A laboratory simulation of plume dispersion in stratified atmospheres over complex terrain

Stratified flows over a three-dimensional topography have been investigated using a stratified towing tank to illustrate airflow pattern and plume behaviors under different conditions, aiming to investigate pollutant dispersion mechanism over Hong Kong Island. The stratified atmospheres are achieved by using stratified salt water. Various towing speeds are used to represent the different wind speeds. Some flow phenomena such as dividing streamline, leeward vortices and leeward wave are observed to explain the causes of high pollution over Hong Kong Island.

Raman Spectra from Pesticides on the Surface of Fruits

Raman spectra of several vegetables and fruits were studied by micro-Raman spectrometer (514.5 nm) and Near-infrared Fourier Transform Raman spectrometer (FTRaman). It is shown that at 514.5 nm excitation, most of the spectra are from that of carotene with some very strong fluorescence in some cases. While at 1064 nm wavelength excitation, the spectra from the different samples demonstrate different characteristic Raman spectra without fluorescence. We discuss the spectroscopic difference by the two excitation wavelengths, and the application of Raman spectra for detection of pesticides left on the surface of vegetables and fruits. Raman spectra of fruits and pesticides were successfully recorded, and using the FT-Raman spectra the pesticides left on the surface of the fruits can be detected conveniently.

Characterization of a Noncolinear Acousto-Optic Tunable Filter and its Resolution Enhancement as a Near-Infrared Spectrometer

An automatic near-infrared (NIR) spectrometer based on a noncolinear acousto-optic tunable filter (AOTF) is constructed for high-speed spectrometry. Its initial spectral characteristics are studied systematically for application. The AOTF is a solid-state, rugged, compact, and high-speed device and can be readily used for spectral measurement applications, but some broadening and overlapping effects will occur when it is used for the measurement of a narrow-band spectrum. In order to correct the spectral distortion and obtain a fine spectrum, a new resolution enhancement procedure, which combines conventional Fourier self-deconvolution (FSD) with our optimized evaluation function and objective parameters determination, is used to resolve the band-broadened and band-overlapped spectral lines. The self-deconvolved spectrum is in good agreement with the fine spectrum measured by a high-resolution grating spectrometer. This is, to our knowledge, the first resolution enhancement of an AOTF spectrum by analytical and numerical operation.

Acousto-Optic Differential Optical Absorption Spectroscopy for Atmospheric Measurement of Nitrogen Dioxide in Hong Kong

Measurement of the atmospheric concentration of nitrogen dioxide (NO2) pollutant was demonstrated by differential optical absorption spectroscopy (DOAS) using a visible acousto-optic tunable filter. In a traditional spectral scanning DOAS system for atmospheric concentration monitoring, a highly stable light source is required. When the light intensity fluctuates during scanning, the concentration retrieval will be inaccurate. In order to reduce the error due to intensity fluctuations, a modified DOAS system has been developed by introducing a broadband light intensity monitoring channel. Using the measured intensity of the broadband channel as the intensity of the light source, the spectrum can be de-biased and the residual intensity variation will primarily result from atmospheric extinction. In addition, by employing the lock-in detection technique, the background light interference is also removed in the modified DOAS system. The atmospheric NO2 concentration measurement was performed at the campus of City University of Hong Kong, and the results were compared with the concentration reported from a nearby monitoring station in Sham Shui Po, operated by the Hong Kong Environmental Protection Department.

The development of telemedicine in Hong Kong

The merging of computers and technologies is facilitating the trend toward remote work arrangements. Telemedicine is a kind of remote work arrangement that is specifically adapted for the health care industries. Telemedicine is seen to be an important potential solution in improving the effectiveness of public services in a community with a limited number of medical experts and other related resources. This article first discusses the needs of telemedicine in Hong Kong and then investigates the current development of telemedicine in Hong Kong and its ability to support collaborative work through image‐transfer and video‐conferencing between professionals across different health care organizations. A model for the development of telemedicine is proposed that includes networked hospitals, remote medical experts, and remote patients. How the proposed model can be implemented, based on existing development, and the benefits it brings are discussed.

Horizontal eye-safe Mie lidar for monitoring of urban aerosols in Macao

A new horizontal eye-safe lidar system has been developed for long-term monitoring of aerosol distribution over an urban area in Macao. The lidar system using a 532 nm micro-pulse laser is made eye-safe by expanding the beam diameter to 70 mm. The detector used is a fast photon counting photomultiplier tube with a narrow bandwidth interference filter to cut down the sky background. This system is the first lidar system operated in Macao to study the local aerosol distribution. We will discuss the method of data acquisition and inversion algorithm in this paper. Recent results from such a new lidar system together with some high pollution episodes will be presented. Developments and the possibility of using this lidar for CALIPSO ground validation will also be discussed.

Neural net classifier for satellite imageries

Accurate identification of cloud type is an important aspect of weather forecasting. One of the primary applications of the remotely sensed cloud cover data is to provide synoptic cloud cover information over extensive data-sparse regions; particularly the oceans and deserts. In southeast Asia, information on cloud cover data is obtained from the infrared and visible channels by Geostationary Meteorological Satellite. These imageries contain data of clouds. By extracting the textural features embedded in the images, information on cloud types can be derived and mapped spatially. An artificial neural network is used as a classifier to identify different cloud types through comprehensive training cycles. The architecture of the network used in the present study is multilayered with feedforward and backpropagation. The study makes use of a classification scheme based on the SYNOP code of the World Meteorological Organization (WMO). The average cloud classification accuracy obtained in this study is 40%.

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 Fernalds 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 Kings 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.

Microcomputer-based image processing system for CT/MRI scans: II. Expert system

A microcomputer-based image processing system is used to digitize and process serial sections of CT/MRI scan and reconstruct three-dimensional images of brain structures and brain lesions. The images grabbed also serve as templates and different vital regions with different risk values are also traced out for 3D reconstruction. A knowledge-based system employing rule-based programming has been built to help identifying brain lesions and to help planning trajectory for operations. The volumes of the lesions are also automatically determined. Such system is very useful for medical skills archival, tumor size monitoring, survival and outcome forecasting, and consistent neurosurgical planning.