Role of Photogrammetry and Remote Sensing in Wenchuan Earthquake

Deren Li

Phase II was marked by the prevention of and preparedness for secondary disasters, i.e., landslides and mudslides, especially, those in and around the quake lakes or barrier lakes. Figure 5 clearly highlights the change of river water ways due to the forming of quake lakes in Tangjiashan, as indicated by white regions generated by comparing SPOT5 (10 m resolution) images taken before (November 10, 2006) and after (May 16, 2008) the earthquake. Figure 6 shows the DEM of the quake lake in Tangjiashan, Mianyang city, Sichuan Province, one of the area worst affected by Wenchuan earthquake, which was generated based on ALS50 II air-borne LiDAR data with a sampling interval of 2 m, flight date, May 31, 2008, by the State Bureau of Surveying and Mapping and Wuhan University (the barrier dam is shown with an inset
picture) in collaboration. The boundaries of rivers in the quake lakes, Tangjiashan, Mianyang city, Sichuan Province, are shown in Figure 7, as indicated by the green lines against the backgroundRadarsat imagery at a resolution of 7 m, acquired on May 17, 2008.

Figure 7. The boundaries of rivers in the quake lakes, Tangjiashan, Mianyang city, Sichuan Province, as indicated by the green lines against the background Radarsat imagery at a resolution of 7 m, acquired on May 17, 2008.

In addition to disaster relief efforts, D-inSAR can also be used for scientific research on earthquake. Preliminary results derived from ALOS PALSAR satellite acquisition on June 11, 2008 are released at www.gmat. unsw.edu. au/LinlinGe/ Earthquake, as shown in Figure 8, thanks to the efforts of the team led by Dr Linlin Ge. Dr Ge used predicted orbit data in order to produce and deliver the result in NEAR REAL-TIME: 17 hours and 46 minutes, from image capture to results posting on web. The Japanese ALOS PALSAR sensor acquired the Path
477 image on 11 June 2008 1:37 Sydney Time AEST (10/06/2008 15:37:07 UTC; 10/06/2008 23:37 Bejing Time). Image data were available to download from ERSDAC at 11:24AM. Image data (using predicted orbit) were downloaded to UNSW on 11/06/2008 at 16:55. D-InSAR results were generated on 11/06/2008 at 19:05. Post-processed D-InSAR results were uploaded on 11/06/2008 at 19:23.

Figure 8. The image showing the aftershocks, generated by D-inSAR technology based on ALOS PALSAR sensor acquisition, Path 477 image on 11 June 2008 1:37 Sydney Time AEST.

Some concluding remarks are as follows. It has been demonstrated that photogrammetry and remote sensing has played a crucial role in the aftermath of the earthquake in Wenchuan, Sichuan. The rapid data acquisition and information services, especially, those featured with fully automatic, near realtime remote sensing systems without ground control, have contributed greatly to the rescue work and disaster relief
efforts. The specialty of photogrammetry and remote sensing is becoming increasingly visible and its roles are growingly recognized. It is important to develop a national disaster rapid response system that corroborates the work by different agencies and facilitates data and resources sharing. It is necessary to further develop China’s National Spatial Data Infrastructure. Moreover, it should be on the agenda to enhance the capability of high-resolution earth observation systems. Last but not the least, it is necessary to strengthen international cooperation in spatial information science and technology, like International Charter and CEOSS from GEO.

Acknowledgements

Many institutions and people have helped with data acquisition and provision of materials during the project concerning rapid response to Wenchuan earthquake. The diligent work by and kind helps from colleagues home and abroad are gratefully acknowledged.