**3.1 The 1993 Hokkaido Nansei-Oki tsunami**

In 1993, a tsunami accompanied by a M7.8 earthquake off the south–west coast of Hokkaido, Japan, struck Okushiri Island, which is 30 kilometers west of Hokkaido, within 5 minutes after the quake, causing more than 200 casualties. In particular, the Aonae district in the southernmost area of Okushiri Island suffered devastating damage due to an approximately 11-m tsunami that struck from the west coast of the island as well as fire caused during and after the tsunami attack (Murosaki, 1994). Visual damage inspection was conducted using pre- and post–tsunami aerial photographs acquired on 29 October 1990 and 14 July 1993 (one day after the event occurred), as shown in Fig. 8. Because the Aonae district suffered from extensive fire during and after the tsunami attack, it is not possible to discriminate between tsunami and fire damage by the aerial photographs alone. Thus, focusing on the existence of house roofs, the structural damage was categorised into five classes according to the damage area, whether flooded or burned, reported by Shuto (2007). The number of inspected houses and structures was 769, and the result of the structural damage interpretation in Aonae district is shown in Table 1 (Koshimura et al., 2009a). The method to detect the damaged area using SAR image analysis was applied to the tsunami-affected area in Okushri Island. Using a set of pre- and post–tsunami SAR images acquired by JERS (Japanese Earth Resources Satellite), Matsuoka & Yamazaki (2002) calculated the correlation and difference in the backscattering coefficient to represent the changes in the tsunamiaffected area. To detect the impacted area, the discriminant score, Equation (2), was

Application of Remote Sensing for Tsunami Disaster 151

The 2004 Indian Ocean megathrust earthquake occurred on 26 December 2004, creating a gigantic tsunami striking coastal communities over a large area. The earthquake, with a magnitude of 9.3 was the second largest ever recorded and caused the deadliest tsunami disaster in history. The tsunami devastated 11 Asian and African countries, and at least 282,517 people lost their lives. There were two locations to which satellite images were

Banda Aceh, a city in northern Sumatra, Indonesia, suffered more than 70,000 casualties and 12,000 house damage incidents during the 2004 event. We acquired the post–tsunami survey data from JICA (2005), which was based on a visual interpretation of the pre- and post– tsunami satellite imageries (IKONOS) with some random field checks, focusing on the existence of the individual structures' roofs. Figure 16 indicates the post–tsunami survey result in terms of structural damage in the city by JICA (2005). As shown in the right panels of the figure, the use of high–resolution optical satellite images has the capability to detect individual damages and be utilised as a promising technology for post–disaster damage investigation. Throughout the visual inspection of the two satellite images, the remaining roofs were interpreted as "Survived" and the roofs that disappeared as "Destroyed". The total number of inspected buildings in the tsunami-inundated area was 48,910, of which 16,474 were interpreted as destroyed and 32,436 as survived, as shown in Fig. 9 (Koshimura et al., 2009c).

**3.2 The 2004 Indian Ocean tsunami** 

**3.2.1 Banda Aceh, Indonesia** 

applied for tsunami damage detection, Indonesia and Thailand.

Fig. 9. Visual damage inspection results in Banda Aceh, Indonesia


Table 1. Results of structural damage interpretation in Aonae district, Okushiri Island

incorporated, and the values of parameters A and B were modified to 1.277 and 2.729, respectively. Fig. 8 shows a comparison among the results of the visual damage interpretation of the aerial photographs, the post–tsunami JERS/SAR image (Fig. 8(b)) and the discriminant score Z*R1* (or *ZRj*). It is found that Z*R1* represents relatively larger values in severely impacted areas and that Z*R1* (Fig. 8(c)) is likely to be fairly consistent with the results of the visual interpretation (Fig. 8(a)). To increase the capability of the SAR image analysis to detect the tsunami impacted area, further discussion is required to explore the relationships between Z*R1* and the structural damage probability by correlating both with regard to the JERS/SAR resolution.

Fig. 8. Comparison among (a) the result of the visual damage interpretation of the aerial photographs, (b) the post–tsunami JERS/SAR image and (c) the discriminant score *ZR1*

#### **3.2 The 2004 Indian Ocean tsunami**

150 Remote Sensing of Planet Earth

Destroyed or Major damage Flooded by tsunami 417

Burned or Major damage Burned by fire 75 Destroyed Unknown 11

damage) — 143

Table 1. Results of structural damage interpretation in Aonae district, Okushiri Island

Fig. 8. Comparison among (a) the result of the visual damage interpretation of the aerial photographs, (b) the post–tsunami JERS/SAR image and (c) the discriminant score *ZR1*

incorporated, and the values of parameters A and B were modified to 1.277 and 2.729, respectively. Fig. 8 shows a comparison among the results of the visual damage interpretation of the aerial photographs, the post–tsunami JERS/SAR image (Fig. 8(b)) and the discriminant score Z*R1* (or *ZRj*). It is found that Z*R1* represents relatively larger values in severely impacted areas and that Z*R1* (Fig. 8(c)) is likely to be fairly consistent with the results of the visual interpretation (Fig. 8(a)). To increase the capability of the SAR image analysis to detect the tsunami impacted area, further discussion is required to explore the relationships between Z*R1* and the structural damage probability by correlating both with

Destroyed, Burned or Major damage Flooded by tsunami and

Survived (Moderate, slight or no

regard to the JERS/SAR resolution.

Damage category Cause Number of

houses

burned by fire <sup>123</sup>

The 2004 Indian Ocean megathrust earthquake occurred on 26 December 2004, creating a gigantic tsunami striking coastal communities over a large area. The earthquake, with a magnitude of 9.3 was the second largest ever recorded and caused the deadliest tsunami disaster in history. The tsunami devastated 11 Asian and African countries, and at least 282,517 people lost their lives. There were two locations to which satellite images were applied for tsunami damage detection, Indonesia and Thailand.

#### **3.2.1 Banda Aceh, Indonesia**

Banda Aceh, a city in northern Sumatra, Indonesia, suffered more than 70,000 casualties and 12,000 house damage incidents during the 2004 event. We acquired the post–tsunami survey data from JICA (2005), which was based on a visual interpretation of the pre- and post– tsunami satellite imageries (IKONOS) with some random field checks, focusing on the existence of the individual structures' roofs. Figure 16 indicates the post–tsunami survey result in terms of structural damage in the city by JICA (2005). As shown in the right panels of the figure, the use of high–resolution optical satellite images has the capability to detect individual damages and be utilised as a promising technology for post–disaster damage investigation. Throughout the visual inspection of the two satellite images, the remaining roofs were interpreted as "Survived" and the roofs that disappeared as "Destroyed". The total number of inspected buildings in the tsunami-inundated area was 48,910, of which 16,474 were interpreted as destroyed and 32,436 as survived, as shown in Fig. 9 (Koshimura et al., 2009c).

Fig. 9. Visual damage inspection results in Banda Aceh, Indonesia

Application of Remote Sensing for Tsunami Disaster 153

The 2007 Solomon Islands earthquake took place on 1 April 2007 near the provincial capital of Ghizo on Ghizo Island, in the Solomon Islands. The magnitude of this earthquake was calculated by the United States Geological Survey (USGS) as 8.1 on the moment magnitude scale. The tsunami that followed the earthquake killed 52 people. The structural/house damage was focused on Ghizo Island and was caused by the tsunami. First, the QuickBird pan-sharpened composite images of Ghizo Island were acquired pre- and post-tsunami (23 September 2003 and 5 April 2007) to build house inventories for visual damage inspection, as shown in Fig. 11 (Koshimura et al., 2010). The extent of the tsunami inundation zone is determined by the supervised classification based on the NDVI of the post-tsunami satellite

Fig. 11. The structural damage interpretation is divided into four classes: slight/no damage,

Fig. 12. Visual damage inspection results for Ghizo Island, Solomon Islands

**3.3 The 2007 Solomon Islands tsunami** 

imagery (Fig. 12), as already shown in section 2.1.

substantial damage, collapsed and washed away

#### **3.2.2 Phang Nga and Phuket, Thailand**

Phang Nga and Phuket were two of six southern Andaman coast provinces that were damaged by the tsunami. They provinces are famous for sightseeing areas such as Khao Lak and Patong. Therefore, reinforced concrete (RC) buildings are common in this area. Regarding structural damage, 4,806 houses were affected by the tsunami, of which 3,302 houses were destroyed completely, and as many as 1,504 were partly damaged. The maximum water level of approximately 15 m reported at Khao Lak in the Phang Nga province and of 7 m at Kamala and Patong Beach in Phuket gave these areas their respective distinction as the worst and second-worst areas, with structural damage to 2,508 and 1,033 houses, respectively. High-resolution satellite images (IKONOS) taken before and after the tsunami event were used for visual damage interpretation. The pre-event images were acquired on 13 January 2003 and 24 January 2004 for Phang Nga and Phuket; the post-event images were both acquired on 15 January 2005. In a recent study (Gokon et al., 2011), four damage levels were classified "Not collapsed" (moderate, slight or no damage), "Major damage", "Collapsed" and "Washed away," using a QuickBird satellite image with a 0.6×0.6 m2 resolution. However, the 1.0×1.0 m2 resolution of the IKONOS satellite image is not fine enough for a visual interpretation to differentiate the damage levels of buildings. Therefore, the classification of the building damage in this study was limited to "Not destroyed" and "Destroyed" (Koshimura et al., 2009c). The remaining roof buildings were interpreted as "Not destroyed" and those that had disappeared were classified as "Destroyed". Note that the buildings classified as "Not destroyed" may have had some sort of Damage that could be identified by the satellite images. The results of the building damage inspection in residential areas are presented in Fig. 10 (Suppasri et al., 2011a), which shows damaged buildings in residential areas in Khao Lak, Phang Nga province (1,722 destroyed and 1,285 not destroyed) and the populated residential areas in Kamala and Patong, Phuket province (233 destroyed and 1,356 not destroyed). The visual interpretation data resulted in an accuracy of more than 90 per cent after being checked with the investigation data.

Fig. 10. Visual damage inspection results in Phang Nga and Phuket, Thailand
