Assessing damage of flood by using ALOS data in Thua Thien - Hue Province - Vietnam PI: 063 Tran Dinh Lan (1) and Nguyen Van Thao (2) (1) Vice Directo

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1 Assessing damage of flood by using ALOS data in Thua Thien - Hue Province - Vietnam PI: 063 Tran Dinh Lan (1) and Nguyen Van Thao (2) (1) Vice Director of Institute of Marine Environment and Resources (IMER) (2) Head of Department of Marine Database and Remote Sensing, IMER Address:, 246 Danang Street, Hai Phong City,Viet Nam Phone: ; Fax: SUMMARY This study used ALOS satellite data for assessing damages from floods on October, 2 nd, 2007 happened at Thua Thien Hue province in both flooded area and flooded level. Result shows that: flooded area covered 7 districts of Thu Thien Hue Province, included: Thuy, Tra, Phong, Quang, Phu Loc, Phu Vang and Hue City, the highest flooded level reached to 5m. Landuse/cover types such as rural area, 2 crops rice, 1 rice crop + 1 vegetables crop, 2 rice crops + 1 vegetables crop, vegetables + industrial tree crops, urban area and aquaculture ponds were flooded heavily both area and level more than other one. 1. INTRODUCTION Coastal zone in Vietnam center always is flooded and inundation every year. Counting for only Thua Thien - Hue Provinces, excluding every year, over fifty year recently there were seven heavy floods happened. One historical flood happened in early of November 1999 with six days long, effected seven provinces in Vietnam Center, created very terrible damages including 600 peoples were died, houses were swept, houses were submerged, ha of rice field was loss of damaged. Thua Thien - Hue Province was heaviest damage province with 350 peoples died. Not only social economic damage but also environment was polluted and ecosystems damage heavily. Vietnam Center coastal zone creates from lowly strait alluvial deltas, lagoons and river mouths lie between high mountains with step slope along western and big sand dunes along the coast. This area was suffered many typhoon and heavy rain concentrated from September to December. Catchment forest was destroyed heavily in the war and due to un-planed used land resources. River mouths and lagoon inlets are flow out of flood water into the sea are sediment irregular due to long shore sand flow. Thus, flood and inundation usually happen irregular, fast and in large area and it s damage heavily. However, until now prediction and monitoring of flood still are very limited. Remotely sensed data provide the possibility of updating the real time information as well as an overview of the environment in the coastal zone. Specially, information on flood and coastline change can be get from satellite images. In speedy growth of information technology, satellite image processing to extract the interested information is made short, much cheaper and more accurate. In this study, the ALOS satellite data was used to assess damage of flood at the Thua Thien - Hue Province in the Vietnam Coastal Center. This is the result of cooperation between Viet Nam Institute of Marine Environment and Resources and the JAXA in the project Monitoring and Prediction the Coastal Flood in the Vietnam Center Using ALOS atellite Data. The result of study will be important data for monitoring, preventing and mitigating damage of flood. 2. DATA AND METHOD 2.1. Data This study uses two scences of AVNIR-2 images which obtained on 27 May, 2008 to map the landuse/cover, two scences of PALSAR image obtained on 2 October, 2007 for mapping the flooded area and a set of PRISM image obtained on 25 August, 2008 to develop the DEM in the Thua Thien - Hue Province. The UTM topographic maps at scale of 1:50,000 and 1:25,000 were obtained for geometric correction of satellite images and digitize topographic information themes such as roads, river, and stream. 1

2 In order to extract information from satellite images, field trip data are used for comparing the color and shape of features on the image with objects on the Earth surface and measure 10 ground control points of height. The data such as tide, wave in the area were collected for determining the wave height and sea level at the time of obtaining images to identify mean sea level on satellite image Method The map of landuse/cover types was established from AVNIR 2 image processing, the map of flooded area from PALSAR and DEM from the PRISM image. Use the overlay function in the GIS tool to calculate and map the flooded levels of landuse/cover types in the Thua Thien - Hue Province.. The method of the study shows in the Figure 1. Fig. 1. Flowchart of the method 3. RESULTS 3.1. Flooded area of landuse/cover types 2 Fig. 2. The study area The map of landuse/cover was overlaid on the map of flooded area to calculate area and map the flooded area of landuse/cover types. The result of calculation and map was shown in the Table 1 and Figure 3. Tab. 1. Flooded area of landuse/cover types in the Thua Thien Hue Province Landuse/cover types Thuy Tra Phong Phu Loc Phu Vang Quang Rural area Aquacalture ponds crop rice + 1 crop vegetables crop rice crop rice + 1 crop vegetables Hue City

3 Vegetables + industrial tree crops Fields and gardens Phu Bai Airport Urban rea Fig. 3. Map of flooded area of landuse/cover types in the Thua Thien Hue Province 3.2. Flooded level of landuse/cover types The map of landuse/cover types, flooded area and DEM were overlaid together to calculate and map flooded level of landuse/cover types. Flooded level higher 3m Result of calculation and map of flooded level higher 3m of landuse/cover types shows in the Table 2 and Figure 4 with flooded time of one day. Tab. 2. Flooded area higher 3m of landuse/cover types In Thua Thien Hue Province Landuse/cover types Thuy Tra Phong Phu Loc Phu Vang Quang Rural area Aquacalture ponds Hue City 3

4 1 crop rice + 1 crop vegetables crop rice crop rice + 1 crop vegetables Vegetables + industrial tree crops Fields and gardens Phu Bai Airport Urban area Fig. 4. Map of flooded area higher 3m of landuse/cover types in Thua Thien - Hue Province Flooded level from 2 to 3m Result of calculation and map of flooded level from 2 to 3m of landuse/cover types shows in the table 3 and figure 5 with flooded time of one day. Tab. 3. Flooded area from 2 to 3m of landuse/cover types In Thua Thien Hue Province Landuse/cover types Thuy Tra Phong Phu Loc Phu Vang Quang Rural area Aquacalture ponds crop rice + 1 crop vegetables Hue City 4

5 2 crop rice crop rice + 1 crop vegetables Vegetables + industrial tree crops Fields and gardens Phu Bai Airport Urban area Fig. 5. Map of flood area from 2 to 3m of landuse/cover types in Thua Thien - Hue Province Flooded level from 1 to 2m Result of calculation and map of flood level from 1 to 2m of landuse/cover types shows in the Table 4 and Figure 6 with flood time of one day. Tab. 4. Flooded area from 1 to 2m of landuse/cover types In Thua Thien Hue Province Landuse/cover types Thuy Tra 5 Phong Phu Loc Phu Vang Quang Rural area Aquacalture ponds crop rice + 1 crop vegetables crop rice Hue City

6 2 crop rice + 1 crop vegetables Vegetables + industrial tree crops Fields and gardens Phu Bai Airport Urban area Fig. 6. Map of flooded area from 1 to 2m of landuse/cover types in Thua Thien - Hue Province Flooded level from 0 to 1m Result of calculation and map of flood level from 1 to 2m of landuse/cover types shows in the table 5 and figure 7 with flood time of half day. Tab. 5. Flooded area from 0 to 1m of landuse/cover types In Thua Thien Hue Province Landuse/cover types Thuy Tra 6 Phong Phu Loc Phu Vang Quang Rural area Aquacalture ponds crop rice + 1 crop vegetables crop rice crop rice + 1 crop vegetables Hue City

7 Vegetables + industrial tree crops Fields and gardens Phu Bai Airport Urban area Fig. 7. Map of flooded area from 0 to 1m of landuse/cover types in Thua Thien - Hue Province 4. DISCUSSION 4.1. DEM Development With the spatial resolution of 2.5m, PRISM can be used to develop the DEM at scale of 1:10,000 and 1:25,000 in high accuracy. However, in order to develop DEM at this scale, it requested fields data to be compatible. In here, fields data are the topographical map with equivalent scale and field survey data. In the DEM development from satellite image, first and also important step is RPCs model development. In this study, 102 GCPs points collect from basic map with scale of 1:25,000 and field survey were used to create the RPCs with accuracy of 1.25 pixel. The correction of DEM result is very indispensable to improve the DEM accuracy. The surface is covered by landuse/cover types such as forest, bush and building, when correction of DEM result must know the distribution of landuse/cover types to correct DEM. For example, in the areas with dense forest distribution of 20m of high trees, the spectrum of light to detector of the satellite is leaves of tree, not surface. In the areas with palate terrain will have bigger error more than other area in DEM development from satellite. So that, the rsuslt of DEM calculation is not exactly and need to correct. In this study, area of dense forest and palate terrain distribute on the high mountain, the DEM correction is reduced 3 to 20m for each different area based on map of landuse/cover. Other areas of study 7

8 area have lowly error in DEM development because of sparse landcovers. In order to assess the accuracy of the DEM, 10 GCPs points have collected to compare with result of DEM development (table 6) Tab. 6. The error of DEM Name of point Coodination Height from Height from Error (m) X Y DEM Basic map Nui Choi Vinh Phong Chay Lim Canh Duong Phuoc Tuong Cao Doi Da Bao Bach Thanh Ba Go Chan May Average error 2.9 Fig.7. DEM from Forward and Backward images of PRISM data in the Thua Thien - Hue Province 4.2. Flooded level In order to calculate and map the flooded area of landuse/cover types at different flooded level must identify the boundary of flood reach to which height by ovelaying DEM and map of flood area. The result of calculation shows boundary of flood reach to 5m height. In this study, flooded level was divided into 4 8

9 levels. Flooded level higher 3m of height (zone 1) is correlative area where the terrain has elevation of 0 to 2m comparing mean sea level. Flooded level from 2 to 3m of height (zone 2) is the area where the terrain has elevation of 2 to 3m, flooded level from 1 to 2m of height (zone 3) where the terrain has elevation of 1 to 2m and flooded level from 0 to 1m of height (zone 4) where the terrain has elevation of 0 to 1m. In those zone, the area of zone 3 and 4 are higher more than the zone 1 and 2. In the zone 3 and 4, distribution of landuse/cover types is mainly rural and urban area, rice and vegetables field, aquacalture ponds and infrastructures. In the zone 1 and 2, the aquacalture ponds, rice and vegetables field is mainly. Flood can be divided into different levels in order to assess damage of landuse/cover types based on scale of DEM Flooded time The flooded time is one of important parameters to evaluate damage of landuse/cover types. The big and hitorical flood such as historical flood happened on early of November 1999 in the Thua Thien - Hue Province can be monitor by using multi temporal satellite image because flood time is long until 1 week. The flood happened on early of Octobor 2007 in the Thua Thien - Hue Province is less than the historical flood both scale, intensity and time (3 days). This flood is difficult to monitor by satellite data because flood time is very short. In this study, calculation of flooded time is based on information from the People Commutee of Thua Thien - Hue Province Damage level Assessment of damage level of flood needs based on two groups of basic parameters: the first group consists of parameters on flooded distribution area, level, time and landuse/cover types. The second group includes specially knowledge on biology, architecture, construction and flooded objects. For example, if a rice variety of A, B days old has been flooded of more than 3m in 2 days with area of S, so how many percent of its productivity will reduce? This is a difficult problem for person who is not specialist of agriculture. Therefore, in this study, the result is only the calculation of parameters in the first group (flooded distribution area, level, time and objects). However, by using satellite data to calculate parameters in the first group is quickly, cheapper and bigger calculated area comparing other method. 5. CONCLUSION - A method of detecting and assessing damages due to flood by using ALOS satellite data is developed. - Map of landuse/cover in 2008, map of distribution of flooding areas at October 2 nd 2007 and a DEM of Thua Thien Hue coastal area, with scale of 1:25000 are established from ALOS satellite data. - Flooded level of landuse/ landcover types were calculated and represented on map. Rural area, 2 crops rice, 1 crop rice, 2 crops rice + 1 crop vegetables, 1 crop rice + 1 crop vegetables, vegetables + industrial tree crops, urban area, aquaculture ponds were flooded heavily both area and level more than other landuse/ landcover types. - In this study, the assessment of flooded damages to landuse/cover types by using ALOS satellite data has just quantify the flooded areas, level and time of landuse/ landcover types. ACKNOWLEDGEMENTS We would like to thank the JAXA for supporting the satellite images, and the Project Solutions for Environmental Contrasts in Coastal Area for helping the cost of publication for this study. REFERENCES 1. Ake Rosenqvist, Daisuke Ichitsubo, Yuji Osawa, Akihiro Matsumoto, Norimasa Ito and Takashi Hamazaki, A brief overview of the Advanced Land Observing Satellite (ALOS) and its potential for marine applications. The Journal of the Japan Society of Photogrammetry and Remote Sensing, Vol 46, No. 1, pp DEM extraction of PRISM stereo from User s Guide of PCI 10.2., DEM Extraction Module from ENVI.,

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