Visual Analysis of the Air Pollution Problem in Hong Kong

Transcription

1 Visual Analysis of the Air Pollution Problem in Hong Kong CHAN Wing Yi, Winnie [Represented by MAK Wai Ho, Wallace] Department of Computer Science and Engineering The Hong Kong University of Science and Technology (HKUST) Hong Kong ICT Awards 2007: Best Innovation and Research Award ICT07/IR/ CU-18

2 Preface This is the work of a final year thesis (research option of final year project) The research paper will appear in IEEE Transactions on Visualization and Computer Graphics (TVCG). Visual Analysis of the Air Pollution Problem in Hong Kong Huamin Qu, Wing-Yi Chan, Anbang Xu, Kai-Lun Chung, Kai-Hon Lau, Ping Guo IEEE Transactions on Visualization and Computer Graphics (TVCG), vol.13, no. 6, Nov.-Dec (Proceedings of IEEE Visualization/Information Visualization 2007) 2

3 Outline Introduction Background Uniqueness of Air Quality Data Visualization Techniques Experimental Results Conclusions and Future Work 3

4 Introduction Visualization Presents data in pictorial form Visualizes the underlying data effectively Visual analysis Is a visual way for data mining and decision making Performs analysis on the visualization result 4

5 Hong Kong Air Pollution Problem Hong Kong air quality is decreasing tremendously Air pollution problem becomes one of the biggest social issues Causes are still unknown Many hypotheses are proposed without any formal proof yet The spectacular harbor view has been increasingly crippled by massive haze. 5

6 Institute for the Environment of HKUST Maintain a comprehensive database on Hong Kong air quality data Cannot obtain convincing results for high-level correlations with mathematical techniques Demand visualization techniques for analysis 6

7 Uniqueness of Air Quality Data Time-series (hourly-based) Inherited geographic information Multi-dimensional (typically >10 attributes) Important vector field wind speed and direction 1. Precipitation 2. Wind Direction 3. Air Temperature 4. Wind Speed 5. Dew Point 6. Relative Humidity 7. Sea Level Pressure 8. Respirable Suspended Particulates (RSP) 9. Nitrogen dioxide (NO 2 ) 10. Sulphur dioxide (SO 2 ) 11. Ozone (O 3 ) 12. Carbon monoxide (CO) 13. Solar Radiation 14. Air Pollution Index (API) 15. Contributed Pollutant to API (Spans more than 10 years) 7

8 Outline Introduction Visualization Techniques Polar System Parallel Coordinates Weighted Complete Graph Experimental Results Conclusions and Future Work 8

9 Outline Introduction Visualization Techniques Polar System Parallel Coordinates Weighted Complete Graph Experimental Results Conclusions and Future Work 9

10 Polar System Is a common vector representation Is heavily applied by domain scientists in environmental field weak very southwest strong south wind wind lowhigh attribute attribute value value Distance from center Wind Speed Angle from the north Wind Direction Color Scalar Attribute 10

11 Circular Pixel Bars Users select a sector to plot the inside-sector data (i.e. of certain wind direction and speed) The corresponding wind direction and wind speed is obvious for rapid comparisons between sectors 11

12 Outline Introduction Visualization Techniques Polar System Parallel Coordinates Weighted Complete Graph Experimental Results Conclusions and Future Work 12

13 Parallel Coordinates Parallel Coordinates are well-established visualization tool for multi-dimensional data Each parallel vertical axis represents an attribute A data item is plotted by a polygonal line intersecting each axis at the respective attribute data value 13

14 S-Shape Axis for Vector Traditional layout (not intuitive) Circular layout (lots of overlapping) S-style layout An example 14

15 Outline Introduction Visualization Techniques Polar System Parallel Coordinates Weighted Complete Graph Experimental Results Conclusions and Future Work 15

16 Weighted Complete Graph It is used for exploring overall relationship among all data dimensions Each node represents one data dimension Distance between nodes encodes their correlation A correlated B C not really correlated 16

17 Outline Introduction Visualization Techniques Experimental Results Correlation Detection Similarities and Differences Time-Series Trend Conclusions and Future Work 17

18 Correlation Detection Color = Air Pollution Index (API) [solar radiation] [SO 2 ] [O 3 ] RSP is correlated with SO 2 and O 3, but not solar radiation High API value (red pixels) are not found when SO 2 is high, inferring that SO 2 contributed little to API API is strongly correlated with O 3 which is known to experts Some suspicious clusters are shown in [SO 2 ] and [O 3 ] - a blue cluster is seen behind a green one 18

19 Similarities and Differences (1) The Hong Kong society mostly weighs external pollution factors more Pollutants blown in from factories on the Pearl River Delta at the northwest of Hong Kong Local pollution is often ignored Power plants Vehicles and vessels 19

20 Similarities and Differences (2) High SO 2 for most stations: Strong wind Northwest wind External Sources High SO 2 for Kwai Chung: All wind speed Southwest wind Internal sources likely due to cargo ships at Kwai Tsing Container Terminals 9 stations of 3 years data Color represents amount of SO 2 20

21 Time-Series Trend for Tung Chung 2004 and 2005 plots are more similar In 2006 plot, temperature varies dramatically 21

22 Positive Feedback from Users Domain scientists found that the polar system with embedded pixel bar offers easy navigation to explore the data interactively Parallel coordinates show the general relationship for them to compare different data-sets rapidly Weighted complete graph provides correlation overview that is useful for initiating an analysis 22

23 Outline Introduction Visualization Techniques Experimental Results Conclusions and Future Work 23

24 Conclusions Comprehensive System The first attempt designed for air quality analysis Novel Techniques Polar system with circular pixel bars: scalar + vector Enhanced parallel coordinates: vector + time axes Weighted complete graph: correlation overview Significant Application Analyzed Hong Kong air pollution problem Revealed known findings effectively Detected unknown patterns by domain scientists 24

25 Future Work Continue as a long-term project with ENVF Make the system available to the public on Web Incorporate new datasets for further exploration Add animations and other visual aids 25

26 The End Thank You!

27 Q & A Polar system with embedded circular pixel bars Weighted complete graph Enhanced parallel coordinates with S-shape vector axis 27