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Next LEE Lap-shun Scientific Officer Hong Kong Observatory lslee@hko.gov.hk Weather information carries little meaning unless it is related to a specific geographical location. Hong Kong Observatory (HKO), being responsible for issuing weather warnings and forecasts in Hong Kong, has a long tradition of using GIS in processing meteorological and other geophysical data spatially, and presenting them on geographical displays for both internal analysis and external service delivery. The use of GIS at HKO, in its more primitive form, can be traced back to the 1980s when the first computerbased weather radar was implemented to replace the old analogue system. The display of radar return signals on top of a geographical map enabled weather forecasters to follow the movement and development of rain areas in a more efficient manner. As GIS technology advanced, conventional weather charts drawn manually by weather forecasters were replaced with computer-generated charts. The weather forecasters are thus free to switch between different weather elements on the same map or generate multiple overlays to suit his/her analysis needs. The emergence of the Internet in the 1990s was another breakthrough which enabled HKO to expand its range of GIS-type products, from internal analysis for own use, to the delivery of services to external users. In addition to textual information, HKO disseminates through its own website weather observation and forecasts using GIS to enable the public to better appreciate the spatial and temporal evolution of weather situations. In recent years, HKO also made use of Location Based Services (LBS) to increase the efficiency of work and enhance its public weather services. With the aid of LBS, new location-specific services were launched allowing the public to better integrate the weather information in their decision processes. Examples of the Observatory's GIS and LBS applications will be discussed in the following sections. USE OF GIS TO ENHANCE EFFICIENCY GIS is especially useful when it comes to analysing and presenting a large volume of information that spans a wide area, such as data from radar or satellite. The rain areas detected by weather radar, presented in different colours according to the intensities, are overlaid on top of geographical maps to enable the weather forecasters to assess the location and intensity of rain areas. Furthermore, sophisticated GIS tool gives forecasters a cross-sectional view of the storm structure by just a mouse drag on the map. Figure 1 shows how a hail event was revealed from the radar image. Over a wider range, weather-related phenomena such as cloud, fog, dust and aerosol as detected by meteorological satellites are presented to weather forecasters with the aid of GIS. The GIS display software is highly versatile in that it can ingest data from different meteorological satellites.  Fig 1: Cross-sectioning to reveal hail signatures from radar picture To facilitate analysis of different weather phenomena, satellite pictures can be enhanced by assigning different colours to signals detected by different channels and overlaying them on the same map. Figure 2 shows how duststorms are revealed from the satellite image. Besides applications on weather fore- Application LBS in weather and geophysical services  Fig 2: Processed satellite image brings out major features including dust (hazy gray), deep clouds (white), low clouds (pale yellow), high clouds (blue) and vegetation (green) casting, GIS is also widely used by the HKO in other areas such as earthquake monitoring. An earthquake monitoring system empowered with GIS features displays earthquake information such as location and magnitude on a map, with visual and audio alarms available so that the Observatory's personnel can respond immediately to the earthquake. Just like other GIS tools with high portability, the earthquake monitoring software is shared for operational use by different countries, which can add to the maps their own geographic overlays such as local roads, bridges and facilities vulnerable to earthquake damage, thus facilitating rescue and rehabilitation work. Figure 3 is a sample screenshot of the earthquake monitoring system. USE OF GIS AND LBS IN THE INTERNET AGE Apart from using GIS to display weather information in such a manner that forecasters could assimilate it conveniently and effectively, the combined use of GIS and Internet had enabled HKO to expand and enhance its service to the public. With increasing bandwidth, weather forecast charts, previously only available to forecasters, are now available on the Internet, empowering citizens to make intelligent weather-related and location-specific decisions for themselves (Figure 4). Another example is the Observatory's lightening location information service provided to the public over Internet, freely. The service is well received, with millions of webpage hits per year. Locations of lightening strokes detected by the Observatory's lightening location network are displayed in graphical form on the Observatory's website and Personal Digital Assistant (PDA) website. With the service adopting GIS technology, users can interactively zoom in to their areas of interest and such geographic features as landmarks, highways, country parks and beaches can be switched on and off at the fingertips of users. Another feature of the service involves the provision of a user-friendly decision support tool. Members of the public can select their own location of interest so that the webpage will automatically provide audio and visual alerts when lightning strokes are detected within a pre-set distance from the specified location (Figure 5). Besides the above, the lightning service  Fig 3: The earthquake monitoring system displays earthquake locations using symbols of different size and colour in accordance with the magnitude and time of earthquakes.  Fig 4: Forecast weather chart for the public Fig 8: Display of in situ wind and temperature measurement from the portable automatic weather station (denoted by CBRN in the map)  Fig 5: Alarm is triggered when lightning activities come close to the user (The "+" symbol in the centre denotes the location specified by user, and the circle denotes the pre-set 15 km-radius alert area.)  Fig 6: Lightning information overlaid with weather radar image Page 1 of 2
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