NASA provided satellite images of Sendai, Japan before and after the 9.0 earthquake and tsunami hit and devastated the region on March 11, 2011. The images vary in spatial resolution. One set of images came from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on NASA’s Aqua and Terra satellite. MODIS provides daily reflectance data of the entire Earth’s surface that are specifically designed for land and water applications with spatial resolutions as small as 250 m. The other set of images came from the imaging instrument Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) flying on Terra. ASTER has a much higher spatial resolution of 15 m, which means you could see more details of the earth’s surface.

NASA Image of Tsunami Damage near Ishinomaki, Japan


I used the ASTER images to map the tsunami damage near Ishinomaki, Japan, which is one of the major affected areas. Note that the classified maps below produced in this analysis are a rough estimation of the extent of flooding caused by the tsunami. The first map result was derived from the August 8, 2008 image. The classification shows water levels (blue color) under normal circumstances. The red color represents the vegetated/agricultural/forested areas, while the green represents the urban/soil areas (I combined both for simplicity).

Ishinomaki, Japan on August 8th 2008

Now here is a classified image of Ishinomaki, Japan for the March 14, 2011 data — three days after the earthquake and tsunami. Again, water is in blue, urban/soil areas in green, and vegetated/agricultural/forested areas in red.

Ishinomaki, Japan on March 14, 2011

What differences can you detect? First, water inundated the city. Days after the tsunami, water still covers what was before just flat fields. Look how water devastated the vegetated/agricultural/forested fields (spread of the green color inland) leaving just bare soil, probably dirt. According to my analysis, and based on the images, about 51 km^2 have been changed to urban/soil/dirt in 2011 from another class in 2008. Notice how the Matsushima Air Base in the lower left corner of the image has been surrounded by water.

Note: The satellite images provided cover a much bigger area, including the one in Sendai. For this analysis, I used a subset of about 304 km^2. For any of you who would want to map the same, I used ENVI software to do the analysis. You can use supervised classification by establishing the regions of interest (ROI) first.

If you have produced maps as well, kindly leave your links in the comment section. My analysis was roughly done for the sake of visualization of tsunami extent. In fact, for those who are into GIS and RS, misclassified pixels are easy to detect.