09155183 d essay

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09155183 d essay

  1. 1. The Hong Kong Polytechnic University Department of Land Surveying and Geo-Informatics LSGI4321 09155183D As a GIT consultant, you are instructed by Hong Kong Observatory toreview their homepage on weather for the public. Please critically review the strength and limitations of the technologies employed and suggest improvements in GIT aspect.A. Background Weather informationsuch as temperature, rainfall, humidity, air pressure, wind speed and direction, are highly correlated with spatial and temporal data. To store, analysis and present these data,Geographic Information System (GIS) is an efficient and reliable platform. Hong Kong Observatory (HKO) has been adoptingGeographic Information System (GIS)to processing meteorological and other geophysical data spatially, and presenting them ongeographical displays for both internal analysis and external service delivery(Lee, 2007) from 1980s.Therefore, the public weather services such as weather warnings and forecasts can be enhanced by making use of GIS technologies. As a result, the public can get a better understanding of the current weather situation through the homepage of Hong Kong Observatory.B. Introduction of technologies employed by HKO Numerical Weather Prediction (NWP) Since 1980s, the Hong Kong Observatory has been using numerical weather prediction (NWP) to forecast weather. For the numerical weather prediction (NWP), a set of equations of a numerical model that describes the evolution of the atmosphere is solved by a high-speed computer.The meteorological parameters considered by the numerical model include temperature, wind, pressure and moisture content.(HKO, 2010) The numerical model represents the atmosphere by a three-dimensional grid set up by systemically arranged points with the values of the meteorological parameters. The larger the set of grid points, the finer the model resolution and more details in the future state of the atmosphere can be describe, but the computational demand is also higher.(HKO, 2010) For forecasting large-scale weather systems such as surges of the winter monsoon, the Hong Kong Observatory adopted the numerical weather prediction
  2. 2. The Hong Kong Polytechnic University Department of Land Surveying and Geo-Informatics LSGI4321 09155183D models of the European Centre for Medium Range Weather Forecasts and the United Kingdom Meteorological Office received in the form of grid point values via the Global Telecommunication System, as well as the numerical weather prediction products from the Japan Meteorological Agency (JMA). (HKO, 2011) For short-range forecast, the Hong Kong Observatory runs an Operational Regional Spectral Model (ORSM) from the Japan Meteorological Agency (JMA) on a high speed computer. This spectral model has a resolution of 20 km and produces forecasts up to 48 hours. (HKO, 2010) Since 2010, the Non-Hydrostatic Model (NHM) implemented by the Hong Kong Observatory (HKO)has been running by a high-speed computer cluster, the NWP Integrated Computing Environment (NICE) to coverthe lower end of the mesoscale weather systems. And mesoscale weather systems refer to weather systems with horizontal scales ranging from a few to several hundred kilometers.The Non-Hydrostatic Model (NHM) has horizontal resolutions of 2 km for inner domainand 10 km for outer domain.(HKO, 2010)C. Strengths of technologies employed by HKO With increased computer speed and memory resources, a fine resolution of 2 km by 2 km grids with a short analysis time can be provided by the Non-Hydrostatic Model (NHM) implemented by the Hong Kong Observatory (HKO). Such a small grid size can allow a higher resolution and more details model. Moreover, the accuracy of the model can be enhanced. The 10-km NHM is run eight times a day to generate 72 hour forecasts and the 2-km NHM is run every hour to generate 15 hour forecasts. Prognostic weather charts and other post-processed products are made available to forecasters as early as 1 hour and 3 hours after analysis time for 2-km NHM and 10-km NHM respectively.Therefore, more timely and detailed objective guidance for formulating weather forecasts and time-critical warnings of inclement weather can be provided.(HKO, 2010) With the data supported by the analysis of the non-hydrostatic model, the Hong Kong Observatory has implemented a spatial weather information service called “Digital Weather Forecast”. It presents weather forecast in fine spatial and temporal resolution.(TONG, 2011) There are two types of forecast products, forecast map and time series provided
  3. 3. The Hong Kong Polytechnic University Department of Land Surveying and Geo-Informatics LSGI4321 09155183D by the Digital Weather Forecast. For the forecast time series, the forecast time charts of a specific region of a grid size 10 km x 10 km in Hong Kong can be produced. It can show the time variation of various weather elements such as temperature, wind and relative humidity within three days.For the forecast map, the data in each grid box, about 10 km x 10 km in size, on the map shows the general weather situation over the region as forecast by the model.It can show the variation of various weather elements such as temperature, wind and relative humidity within three days graphically.Both of the two products are updated twice a day, hence, a updated graphical representation of weather forecast can be reviewed by the public through the homepage of the Hong Kong Observatory easily.D. Limitations of technologies employed by HKO Firstly, for the products of “Digital Weather Forecast” implemented by the Hong Kong Observatory, the smallest grid size for data analysis is 10 km X 10 km. The value of various weather elements such as temperature, wind and relative humidity in each grid on the map shows the general weather situation over the region as forecast by the model. However, as each grid box is relatively large which is about 10 km X 10 km, it may comprise a wide range of geographic characteristics such as land mass, sea surface, hill and valley. Therefore, the weather conditions described by the products may be not fine in resolution and different from those recorded at individual weather stations within the grid box and the weather forecasts issued by the Observatory.(HKO, 2011) For that reason, as limited by the resolution of the numerical model, the “Digital Weather Forecast”is only suitable for overviewing the general weather condition of a relatively large area, but not accurate to preview the weather of a specific place or a relatively small area, for example, a housing estate.Therefore, it might not useful for the user to find the weather condition of his current position by using the “Digital Weather Forecast”. Secondly, the forecast map generated by the “Digital Weather Forecast”only contains the map with the outline of Hong Kong andlegend showing the value of various weather elements such as temperature, wind and relative humidity. It is
  4. 4. The Hong Kong Polytechnic University Department of Land Surveying and Geo-Informatics LSGI4321 09155183D lack of the geographic information of the map, for examples, the road features with their names, the building features with their names, the names of the districts and location, and so on. Moreover, the scale of the map is fixed and relatively small where the area of the map has also including the Pearl River Delta. However, the weather forecast of the Pearl River Delta may not necessary for the majority of local users.The more detail in the map of Hong Kong maybe more appreciated. Furthermore, for those map users who are not familiar with the location of district and places in Hong Kong, they may have to spend more time onreferring to a general map to find a specific location on the forecast map produced by the “Digital Weather Forecast”.Therefore, the forecast map may not be convenient and user-friendly for the intermediate map users. The last but not least, the Numerical Weather Prediction model (NWP) adopted by Hong Kong Observatory do not consider the 3-D urban model.However, urban areas have many ‘roughness’ elements such as buildings, trees, masts, street furniture andvehicles. As the wind blows over urban areas, the air interacts with these roughness elements andresponds according to their size, shape, layout and distribution. (Evans, 2009)These interactions have great impact on the weather forecast, especially for the urban area like Hong Kong. However, the Hong Kong Observatory does not take these urban elements into account. Therefore, the analyzed result for the weather forecast maybe not accurate and reliable and different from the weather information recorded at the individual weather stations of the Hong Kong Observatory.E. Suggested Improvements In order to increase the detail of the map productfromthe “Digital Weather Forecast”, the Hong Kong Observatory can utilize the existing Non-Hydrostatic Model (NHM)of grid size 2 km X 2 km which is implemented by itself, instead of the Non-Hydrostatic Model (NHM) of grid size 10 km X 10 km. If the grid size of the numerical weather prediction model is decreased, the resolution of the weather forecast map can be increased. The area represented by one grid can be reduced greatly from 100 km sq. to 4 km
  5. 5. The Hong Kong Polytechnic University Department of Land Surveying and Geo-Informatics LSGI4321 09155183Dsq. As less geographic characteristics such as land mass, sea surface, hill andvalley would be include in a smaller grid, the expected variation of weatherconditions such as temperature and relative humidity within a grid box would besmaller and closer to the actual values. Therefore, the overall accuracy ofproducts from the “Digital Weather Forecast” can be enhanced and it is possibleto preview the weather of a specific place or a relatively small area.Moreover, the “Digital Weather Forecast” can be associated with the geographicinformation. The data of the “Digital Weather Forecast”is in the format of OpenGIS standard KML 2.0 where KML stands for Keyhole Markup Language. There area number of KML-supported GIS display software packages. Users can choose theappropriate software such as Google Earth according to their own needs.Through GIS display software, users can zoom in, zoom out, animate and overlayother geographic information on the weather forecast maps to better appreciatethe weather conditions in their area of interest.(HKO, 2011)As a result, the products from the “Digital Weather Forecast” can become amulti-scale digital forecast map.The map user can search the information ofweather forecast and other geographical information of any point on map easilyin the homepage of the Hong Kong Observatory. The forecast map would bemore user-friendly.To forecast weather accurately, the interaction between meteorology and theurban environment can be modeled. The numerical weather prediction modelused by the Hong Kong Observatory is grid-based which is using a regular gridwith each cell resenting a value, such as temperature, air pressure and so-on.And the 3-D city models are usually vector based. 3-D city model can be takenand developed to create input data for a numerical weather predictionmodel.(Evans, 2009)Although constructing and maintaining a 3-D city model with fine details for HongKong is costly and time-consuming, the detailed spatial analysis can be carriedout and the quality of the weather forecast can be ensured. In the data analysis,the interaction between the urban environment and the numerical weatherprediction models can be took into account. Therefore, the analyzed result of theweather forecasting would be more reliable than the conventional method ofHong Kong Observatory that only considers the numerical weather prediction
  6. 6. The Hong Kong Polytechnic University Department of Land Surveying and Geo-Informatics LSGI4321 09155183D models.F. ConclusionThe Hong Kong Observatory has provided many useful public services of issuingweather warnings and forecasts by using the Geographic Information System (GIS)technology on its homepage. It has been developed and enhanced spatial weatherinformation services such as “Digital Weather Forecast” for the public and specialusers with a view to supporting their decision-making in relation to weather-sensitiveactivities (TONG, 2011) .However, there are some weak points in these services, for examples, the accuracyand user-friendliness. As the “Digital Weather Forecast” provided is in beta-version,it can look forward to the improvement on it, as well as other weather services whichare making use of GIS technologies, in the near future.
  7. 7. The Hong Kong Polytechnic University Department of Land Surveying and Geo-Informatics LSGI4321 09155183DReferenceEvans, S. (2009). 3D cities and numeriacal weather prediction models: A overview ofthe methods used in the LUCID project. London: Centre for Advanced Spatial AnalysisUniversity College.HKO. (2011, 11 3). Digital Weather Forecast. Retrieved 11 3, 2011, from Hong KongObservatory: http://www.hko.gov.hk/dfs/main/dfs_tt_e.htmlHKO. (2010, 9 30). Mesoscale Model. Retrieved 11 3, 2011, from Hong KongObservatory: http://www.hko.gov.hk/nhm/mesomodel_e.htmHKO. (2011, 8 15). Numerical Weather Prediction Models. Retrieved 11 3, 2011, fromHong Kong Observatory: http://www.hko.gov.hk/aviat/amt_e/nwp_e.htmLee, L. (2007). GIS and LBS Applications in the Delivery of Weather and GeophysicalServices in Hong Kong. Hong Kong: Hong Kong Observatory.TONG, Y.-f. (2011). Recent Development of Location-based and Spatial WeatherInformation Services by the Hong Kong Observatory. 7th Annual Seminar on SpatialInformation Science and Technology (p. 3). Hong Kong: Department of LandSurveying and Geo-Informatics of the Hong Kong Polytechnic University.

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