Using Idrisi to Analyze the Destruction of Tsunamis

Sarah Pick

Fall 2011
ES 775 Advanced Image Processing
Dr. James S. Aber, Instructor

Table of Contents
Introduction
Methods
Before and After Images
Conclusions
References


Introduction

The National Ocean and Atmospheric Administration defines tsunamis as a set of ocean waves caused by any large, abrupt disturbance of the sea-surface (2011). With modern technology, such as satellites, scientists can now study the destruction of tsunamis. Different bands can be used to determine the extent of the damage, depending on which feature one chooses to focus on. The most common features that are compared include changes in anthropogenic structures, vegetation, and sediment load in water systems. The satellite used in this study carries a Thematic Mapper (TM) sensor system. Each band used by the satellite has a different wavelength and can be used to emphasize particular features.

Band
Color
Wavelength (micrometers)
Applications
Band 1 
Blue
0.45- 0.52
Provides increased penetration of water bodies, supports analyses of land use, soil, and vegetation characteristics
Band 2
Green
0.52- 0.60
Corresponds to green reflectance of healthy vegetation
Band 3
Red
0.63- 0.69
Important for vegetation discrimination, soil boundary, and geological-boundary delineations
Band 4
Reflective infrared
0.76- 0.90
Responsive to the amount of vegetation biomass present, useful for crop ID and emphasizes soil/crop and land/water contrasts
Band 5
Mid-infrared 
1.55- 1.75
Sensitive to the turgidity of water in plants, useful in crop drought studies/ plant vigor investigations, and discriminates between clouds, snow, and ice
Band 6
Thermal infrared
10.4- 12.5
Measures amount of infrared radiant flux emitted from surfaces, useful for locating geothermal activity, vegetation classification, vegetation stress analysis and soil moisture studies
Band 7
Mid-infrared
2.08- 2.35
Discriminates geologic rock formations

Chart summarizing the bands of the Thematic Mapper, Jenson, 2000.

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Methods

A list of major tsunamis was obtained from the International Tsunami Information Centre. Using Glovis (Global Visualization Viewer), an archive of Landsat datasets provided by the U.S. Geological Survey, dates and locations of tsunami destruction were observed. Most of the localities did not have a dataset for the desired time periods; other datasets contained too much cloud cover to be particularly useful. In the end, one location was chosen for this project: two sections of the country of Bangladesh, the areas around Dhaka and Galachipa. The tsunami being studied was caused by the 26 December 2004 Indian Ocean earthquake. It had a magnitude that ranged from 9.1 to 9.3, with its epicenter off the west coast of Sumatra. Before and after images of the area were obtained.


Map showing location of Dhaka, Bangladesh (A) and Galachipa, Bangladesh (B), courtesy USDA, 2011.

Less than 40 miles west of Galachipa is the Sunderban National Park. This Park is visible in the Galachipa images. Vegetation, mostly mangrove forests, thrives year-round due to irrigation systems throughout the National Park. This National Park is also the last home of the Bengal Tiger (UNESCO, 2011).

After the images were obtained, data had to be extracted from the zipped files. Located in each zipped file were large individual files for each band (these files were in the form of 'tifs'). The 'tif' files were then imported directly into Idrisi (by selecting File, Import, Government, Landsat). When the B10 band was selected for band 1, all of the other bands filled in automatically. After importing the images, a subscene was created for each. This is done by selecting Reformat and then Window. Each of the bands for each image was selected for this function.

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Before and After Images

before
after

Before and after images of Dhaka, Bangladesh, using bands 3, 4, and 5. Note that other than a decrease in vegetation, there doesn't appear to be much of a change.

before
after

Before and after images of Dhaka, Bangladesh, using bands 3, 4, and 5.

before
after

Before and after images of Dhaka, Bangladesh, using bands 1, 3, and 7. Black areas represent water bodies, green areas are sediment load in the river, and red is vegetation. Note that in the before image, a small branch of the river in the north is the only locality with sediment load; however in the after image, after the tsunami, most of the river is carrying a lot of sediment.

before
after

Before and after images of Dhaka, Bangladesh, using bands 1, 3, and 7.

before
after

Before and after images of Galachipa, Bangladesh, using bands 3, 4, and 5.Dark green areas on the left side of the image represent the Sundaban National Park. Agriculture and fields are visible on the right side of the image.

before
after

Before and after images of Galachipa, Bangladesh, using bands 3, 4, and 5.

before
after

Before and after images of Galachipa, Bangladesh, using bands 1, 3, and 7. Note the light blue color of the sediment load before the tsunami versus the dark green color after.

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Conclusions

Idrisi can be used to analyze the destruction of tsunamis by looking at sediment load. In order to better understand how to use this tool, one must posses a lot of time and patience to spend the time looking up and working with acceptable images. Bands 3, 4, and 5 were best for determining changes in vegetation and water/land boundaries. Bands 1, 3, and 7 were best for studying changes in sediment load in water bodies.

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References

Aber, J.S., 2011. ES 775 Lab 6. http://academic.emporia.edu/aberjame/es775/lab06/lab06.htm. , accessed 1 December 2011.

International Tsunami Information Centre, 2011. Tsunami Events. http://ioc3.unesco.org/itic/categories.php?category_no=77. , accessed 30 November 2011.

Jenson, J.R., 2000. Remote Sensing of the Environment An Earth Resource Perspective. Prentice-Hall, Inc., Upper Saddle River, New Jersey.

National Oceanic and Atmospheric Administration (NOAA), 2011. The Tsunami Story. http://www.tsunami.noaa.gov/tsunami_story.html. , accessed 7 December 2011.

UNESCO, 2011. Sundarbans National Park. http://whc.unesco.org/en/list/452/. , accessed 9 December 2011.

United States Department of Agriculture (USDA) Farm Service Agency, 2011. Galachipa, Bangladesh. http://maps.google.com/maps?hl=en&tab=wl. , accessed 6 December 2011.

United States Geological Survey (USGS), 2011. USGS Global Visualization Viewer. http://glovis.usgs.gov/. , accessed 1 December 2011.

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