A Study of Areospace Reconnaissance of Earthquake Sites

A Study of Areospace Reconnaissance of Earthquake Sites

Tsuyoshi Kondo*, Takeshi Doihara*
Osamu Uchida**, Hirokazu Muraki**

Asia Air Survey Co,.Ltd. Research Institute
* 8-10 Tamura-cho, Atsugi, KANAGAWA, 243 Japan
** 2-1-11 Esaka-cho, Suita, OSAKA, 564 Japan

This paper proposes effective utilization of image resources of earthquake sites. After the Southern Hyogo Prefectural Earthquake, more than 10,000 aerial photographs were taken and have been effectively used for relief activities, prevention of multi-hazard, restoration, and redevelopment planning. However, even with aerial information support, unexpectedly tremendous time and labor have been spent after the tragic earthquake because of mobilization delay which was caused by untimely recognition of the extent of the darnage. To solve this problem, we have surveyed requirements of information in the disaster of the quake and have found that instant availability of information is the most important factor right after the quake; accuracy will be required only in later stages. Aerial photographs do not have instant availability because of wet-process, even though they can satisfy the accuracy requirement. Since high resolution satellite imagery will become available after 1997, we used simulated images to analyze the potential for interpretation, measurement and mapping. We have come to the conclusion that high resolution satellite imagery has instant availability but does not have accuracy, and therefore can be complementary when used together with aerial photographs to effectively help damage reduction and quick restoration of earthquake sites.

Introduction
In Japan where earthquakes occur frequently, it is important to collect accurate information of damage in the early stages of quake disaster to decide proper and efficient mobilization of relief activities. Aerial photography is one of many spatial data media which record damage situations of disaster areas. Right after the Southern Hyogo Prefectural Earthquake in early 1995, more than 10,000 aerial photographs were taken in five days after the quake broke out (Rikimaru, 1995). These photographs provided data for damage recognition, mapping, and 3-D measurement (see Fig. 1). The following objects and situations were found to be recognizable by interpreting the photographs (Doihara, 1995; Yoshizawa, 1994; Suzuki, 1995; Tsukaguchi, 1995; Toyama, 1995):

O collapsed houses (wooden,steel-frames,reinforcedconcrete)
O slope failure, landslide blocks
O falling, insulation, subside, blockade of roads and railways
O liquefaction/ sandboiling(seeFig.2)
O derailedtrains
O trafficjams
O coastatpollution
O Iineaments,faults
O collapsedharborfacilities
O collapsedtombs
O burneddownarea
O crackedshoreprotectingstructures

However, even with aerial information support, unexpectedly tremendous time and labor have been spent after the tragic earthquake, because of delay of initial motion (Kawata, 1995). Shibazaki (1995) points out that this delay was primarily caused by untimely recognition of damage situations in early stage.

Fig 1. Distrubution of geographical displacements in western Kobe city by means of stereoscopic measurement

Fig 2. Distributions of liquefaction among the Osaka-bay
In this paper, we discuss effective utilization of image resources for earthquake sites. First, we review information requirements in the quake disaster, and discuss the applicability of the information of aerial photography. Next, we evaluate the applicability of high resolution satellite imagery, which is scheduled to be regularly available from the beginning of 1997, to aerospace reconnaissance in a disaster area by using simulated images. Finally, we discuss complementary utilization of aerial photography and high resolution satellite imagery to help damage reduction and quick restoration of the earthquake sites.

Requirements of Information and Reconnaissance with Aerial Photograph in the Desaster of ] southern Hyogo Prefectural Earthquake
We have summarized the information required after the quake broke out by surveying news clips reported by newspapers related to aerial photographs. Table. 1 shows information requirements at each stage of the disaster and the actual reconnaissance processes with aerial photography in the disaster of the Southern Hyogo Prefectural Earthquake.

Information Requirements

(1) The stage of extinguishing fire/emergency response (after 10 minutes, up to 3 hours) The disaster declaration was announced by Osaka Meteorological Observatory 10 minutes after the quake broke out. Prevention from fire and gas explosion is pressingly needed. Recent research shows that damage assessment information system is indispensable to determine appropriate mobilization activities in this stage.

(2) The stage of relief (after 3 hours, up to 3 days) Relief requests were issued by the municipalities in the disaster area within twelve hours of the quake. Pressing needs in this period were to locate the damaged spot and to recognize the damage scale. TV news broadcast images of the disaster area which were obtained by field survey and reconnaissance by helicopter. Without geographical information, it was too difficult to identify the disaster area and damage scale for people who do not have the feel of the place. Aerial reconnaissance began in this stage.

The government decided to enact the law of disaster relief to the damaged area and people started living in shelters. Information requirements about safety and relief became stronger. The aerial photographs of the whole Hanshin area were helpful for integration of fragmentary reports about the disaster and damage scale recognition.

(3) The stage of restoration (after 3 days, up to 1 month) Request of maps had increased for restoration use, and, as a result, bookstores ran out of their stock of atlases and maps. The Geographical Survey Institute and various organizations had made maps of damage distribution such as liquefaction, geographical displacement and collapsed houses by interpreting aerial photographs. The requirement for information accuracy had increased in the stage of restoration, and in some cases it exceeded the accuracy of aerial photography. For example, aerial photograph interpretations do not give enough information for classification of damage grade.

(4) The stage of redevelopment (after 1 month, up to 3 months and later) Notices for the town restoration plan began to be posted. The information of land height and control points ware required for the redevelopment of the darnaged area because the control points of the whole Kobe city had displaced in terms of deformation and destruction caused by liquefaction and/or sliding. Geographical Survey Institute had established twenty precise emergency primary control points surveyed with GPS and sixty-four emergency leveling bench marks (approximately 84km) in Kobe city, especially in the southern area. After the new control points took effect, the new survey results were compared with those from before the quake, and aerial photograph was required for measurement of displacement. Through these stages, fragmentary information had been integrated into ‘area information’ by using aerial photographs and had been refined up to ‘geocoded information’. Requirement for instant availability had been changed to that for accuracy with the passing of time.

Reconnaissance with Aerial Photography
Aerial photographs had also changed their roles to respond to the information requirements referenced above. However, the use of aerial photography resulted in a delayed response to the needs as shown in Table 1. For example, one day was spent for taking photos and developing them for interpretation, although much of the practical information was required within three hours of the quake; Maps of damage situations were released one week after the quake, although some recognition of the actual damage scale was required six hours after the quake. The delay was primarily caused by the required processing time for the analogue media. The process orthorectification (Nishimura, 1995).

It is concluded that aerial photography has physical limitation in instant availability and cannot be used for mobilization planning when a disaster occurs, although it may satisfy the functional requirement.

Applicability of high resolution satellite imagery to earthquake sites
High resolution satellite imagery, which will be one of the image resources from the air, is expected to complement aerial photography. We evaluated the applicability of this new information resource to earthquake sites with simulated images made from aerial photographs.

Outlines of Commercial Earth Observation Satellite
High resolution satellite imagery is one of the military technologies which have been commercialized since the end of the Cold War. EarthWatch communications, Inc. will provide 3m ground resolution satellite imagery beginning in March ’97, and 82cm ground resolution images in early 1998. Space Imaging, Inc. will also start to deliver data which have 82cm ground resolution in early 1998. Some other companies are also planning to launch commercial earth observation satellite after 1998 and large amounts of data will become available for practical use. Table 2 shows the specifications of representative high resolution satellite imageries.

Potential of Satellite Imagerv for Intermetation and Measurement
We evaluated the potential of high resolution satellite imagery in the analysis of disaster areas with simulated images created from aerial photographs. Fig.3 shows the sample of simulated images. Four people tried to interpret thirty-four simulated images with 3m and lm ground resolution. The following objects and conditions were recognizable with each referenced resolution:

Images with 3m ground resolution

Roads with over 20m width and more
Roads with 5m width (ambiguous)
Large constructions such as factories
Houses (small houses were ambiguous)
Damage situations;Landslides, Burned down area, Fall of elevated highway and railroads, Liquefaction of over 1,000m2, Collapse of shore protecting structures, Lineament, Coastal Pollution
Raih-oads (difference from reads was often ambiguous)

Images with lm ground resolution
Objects and disaster conditions which can be recognizable with 1/4,000 contact printed aerial photographs except collapse of small houses

Figure 3. Simulated images of damage situations created form aerial photographs

We have also evaluterd the accuracyof mapping with high resolution satellite imagery. A pair of 3m simulated images are created form 1/20,000 aerial photographs and processed by an automatic stereo matching program. Fig. 4. shows comparison between contours of criterion data and calculatd data. Residuals of reference points in orientation correspond vertical accuracy of 1/25,000 mapping using 1/40,000 aerial phot~graphs, and horizontal accuracy of 1/10,000 to 1/15,000 mapping using 1/30,000 aerial photographs. Ovals in Table 3 indicates the accuracy corresponding to 3-D measurement with 3m resolution satellite imageries. This result indicates that 3-D measurement accuracy with 1m resolution satellite imagery has an accuracy of 1/5,000 to 1/10,000 mapping.

Advantages and Disadvanta~es There are some advantages and disadvantages in application of high resolution satellite imagery to earthquake sites:

Advantages

Request capturing imageries within 1 day (all available high resolution satellite data to be considered) make survey of short-time-sequential changes possible.
Digital imageries are delivered in a few hours after capturing imageries through online data supply and available in the early stage of disaster.
Imageries cover large area at a time and are suitable for investigation of global damage.
Nadir imagery can be regarded as good approximation of orthophoto because the satellite captures imagery at very high elevation with long focal length.
Time sequential imageries can be stored in database and applied to GIS systems for assessment of damage.
Analysis of spectralcharacteristicsof image enables extraction of liquefaction area.
Data ru-eavailable for low price.

Disadvantages

Imagery data tend to be affected by clouds.
Availability of imagery data at specific moment depends on satellite position.

Potential of the high resolution satellite imagery satisfies the requirement for aerospace reconnaissance in the early stages of disaster. It is expected that satellite imagery will supplement the role of aerial photography when they are not available and/or when global damage information is required, while aerial photography will provide information with a high accuracy requirement. INTEGRATED IMAGERY SUPPORT FOR DISASTER STAGES Through the discussion described above, it is clarified that aerial photography provides an information resource which meets the requirement of high-accuracy analysis such as investigation of accurate damage situation and measurement of geographical displacement, where accuracy has a higher priority than processing time. They also can be used for obtaining information in the area which could not be captured by satellite sensors. On the other hand, high resolution satellite imagery has the advantage of wide area coverage and instantaneous online data delivery. It can effectively used for rough estimation of damage conditions in the early stages after a disaster. It also can be used for analysis of changes of the site before and after the disaster by using time-sequential imageries.

Table 4 summarizes our discussion. Satellite imagery databases can be used to assess damage before earthquake with other geographic data. For this application, it is indispensable to update continuously geographic data such as soil type, building type, and simulated results of seismic intensity. A satellite imagery database itself is also used for ordinary GIS data.

Fig.4 Comparison between contours of criterion data and calculated data Naturally, imagery resources obtained via aerospace reconnaissance can not provide all of information in demand. Detailed information such as investigation of casualties and some of relief activities should be supplemented by field survey. Online integration of information obtained by satellite imagery, aerial photograph and result of field survey facilitates the planning for required resources on demand. Multi-media communication technology will enable such an online information system.

Summary
This paper discussed the effective utilization of image resources for earthquake sites. Aerial photography can provide more accurate spatial data than can satellite imagery, while satellite imagery has more instant availability than aerial photography. Therefore these image resources can be used together in a complementary fashion to effectively help damage reduction and quick restoration of the earthquake sites. There is no prevention against earthquakes. Therefore, our effort must focus on prevention against damage caused by earthquake. Is it possible to provide imagery information on demand and analyze it instantaneously? This is a large demand on data providers. All providers of aerial photographs should ensure that their systems address the needs discussed in this paper.

Table 4 Imagery Information support of damage situation by aerospace reconnaissance

References

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