Identifying damage caused by the 2008 Wenchuan earthquake from VHR remote sensing data

Figures & data

Figure 1.  Earthquake-affected area of the Sichuan province north of Chengdu. The location of the epicentre (star) as well as the three towns included in the study are shown.

Table 1. Imagery used for structural damage assessment in areas affected by the Sichuan earthquake.

Location	Sensor	Type	Acquisition date	Spatial resolution
Yingxiu	World-View-1	Optical panchromatic	10-Jun-08	0.5 m
	SPOT-5	Optical panchromatic	7-Nov-05	2.5 m
	Cosmo-Skymed	SAR (SM*)	13-May-08	3 m
Dujiangyan	EROS-B	Optical panchromatic	15-May-08	0.7 m
	TerraSAR-X	SAR (SL*)	15-May-08	1.6 m
	Cosmo-Skymed	SAR (SL)	13-May-08	1 m
	Cosmo-Skymed	SAR (SM)	13-May-08	3 m
Beichuan	SPOT-5	Optical panchromatic	10-Nov-06	2.5 m
	SPOT-5	Optical panchromatic	4-Jun-08	2.5 m
Beichuan District	SPOT-5	Optical panchromatic	4-Jun-08	2.5 m
*SL = Spotlight mode; SM = Stripmap mode.

Table 2. Optical satellite imagery potentially useful for post-disaster damage assessment presented in the order of decreasing resolution. Imagery used in this study are given in italics.

Satellite	Spatial resolution (nadir) [m]	Spectral response [nm]	Swath Width [km]	Minimum site revisit time* [days]	Notes
WorldView-1	0.5	450–900 (pan)	17.6	1.7	Stereo capability
Quickbird	0.6	450–900 (pan)	16.5	1–3.5
	2.4	450–520 (blue)
		520–600 (green)
		630–690 (red)
		760–900 (NIR)
EROS-B	0.7	500–900 (pan)	7	3	Stereo capability
Ikonos	0.8	450–900 (pan)	11	1–3
	4	445–516 (blue)
		506–595 (green)
		632–698 (red)
		757–853 (NIR)
OrbView-3	1	450–900 (pan)	8	3
	4	450–520 (blue)
		520–600 (green)
		625–695 (red)
		760–900 (NIR)
KOMPSAT-2	1	500–900 (pan)	15	5
	4	450–520 (blue)
		520–600 (green)
		630–690 (red)
		760–900 (NIR)
Formosat-2	2	450–900 (pan)	24	1
	8	450–520 (blue)
		520–600 (green)
		630–690 (red)
		760–900 (NIR)
Cartosat-1	2.5	500–850 (pan)	30	5	Stereo capability
SPOT-5	2.5	480–710 (pan)	60	2–3	Stereo capability
	10	500–590 (green)
		610–680 (red)
		780–890 (NIR)
		1580–1750 (MIR)
*Minimum site revisit times at varying viewing angles.

Table 3. Images from satellite-borne synthetic aperture radar (SAR) sensors. Imagery used in this study are given in italics.

Satellite	Max. spatial resolution [m]	Wavelength [cm] (band) polarisation	Minimum swath in fine mode [km]	Orbit repeat cycle [days]*	Year launched
CosmoSkymed	1 (SL**)	3 (X-band)	10	16	2007
	3 (SM**)	HH, VV, HV, VH
TerraSAR-X	1 (SL)	3 (X-band)	10	11	2007
	3 (SM)	HH, VV, HV, VH
RADARSAT-2	3 (SM)	5.6 (C-band)	20	24	2007
		HH, VV, HV, VH
SAOCOM	10	23.5 (L-band)	50	16	2003
		HH, VV, HV, VH
ALOS	10	23.5 (L-band)	40	46	2002
		HH, VV, HV, VH
RADARSAT-1	8	5.6 (C-band)	50	24	1995
		HH
*Site revisit times at varying incidence angles are shorter.
**SL = Spotlight mode; SM = Stripmap mode.

Figure 2.  A 1×1 km² subset of the city of Yingxiu as seen by WorldView-1 (a). The highlighted central area is enlarged in (b).

Figure 3.  A comparison of CosmoSkymed SAR stripmap data at 3 m resolution (a) and SPOT-5 pre-disaster panchromatic imagery at 2.5 m pixel spacing (b) over Yingxiu.

Figure 4.  Image examples over Dujiangyan acquired by EROS-B (a), CosmoSkymed stripmap (b), CosmoSkymed spotlight (c), and TerraSAR-X spotlight (d). The subset outlined in (a) is presented enlarged in Figure 5.

Figure 5.  Enlarged subset of the image chips shown in Figure 4. EROS-B (a), CosmoSkymed stripmap (b), CosmoSkymed spotlight (c), and TerraSAR-X spotlight (d). The damage to the building structure in the central area is well visible on the EROS-B image (a). To a trained interpreter, textural deviations in comparison with intact buildings can serve as an indicator of damage on the spotlight SAR imagery (c, d).

Figure 6.  Landslides interrupting roads upstream from Beichuan depicted on a SPOT-5 panchromatic image.

Figure 7.  Inundated village as seen on a SPOT-5 panchromatic image.

Figure 8.  This figure shows the city of Beichuan on pre-disaster (a) and post-disaster (b) SPOT-5 imagery at 2.5 m resolution. Two large landslides (white arrows) have destroyed parts of the city.

Figure 9.  Pre-disaster SPOT-5 (a) and post-disaster WorldView-1 (b) imagery over Yingxiu. The green circles on both image chips represent detected intact buildings; those that were destroyed during the earthquake are marked with a red×on the post-disaster image. Intact buildings, identified on the post-disaster WorldView-1 data, but not present on the SPOT image, acquired in 2005, are depicted as light green triangles. The image is centred on 31°04′N, 103°29′E.