Assessment of the impact of Dec .26, 2004 tsunami over Andaman and Nicobar Islands using Remote Sensing and GIS techniques

Objectives: The main objectives of our study included:
• Demarcation of inundated area affected by Dec.26 tsunami and take transects across the inundated areas at various locations to measure the `run up’ levels.
• To delineate the shoreline changes using pre and post event images/ maps.
• To map the land use/cover and its changes in tsunami affected area.
• Geomorphological mapping and detection of changes if any.

Study Area:

The Andaman and Nicobar archipelago comprising 572 islands is situated between 60 and 140 N latitude and 920 and 940 E longitude. The island in the extreme south -Great Nicobar- is hardly about 150 kms. from Indonesia, the epicenter of the recent devastating tsunami. Andaman and Nicobar group of islands has been highly vulnerable to earthquakes and falls in zone 1 as per the seismic zonation map of India prepared by Bureau of Indian standards (BIS). The Andaman Group stretches over 700 km. in length with a maximum breadth of 51 km. These Islands have a tropical climate with an average annual rainfall of 3180 mm and humidity as high as 87% and are endowed with of a thick evergreen tropical forest covering more than 92% land area.
Although the study area for this project included all the major southern group of islands present report deals with the work done in the last 1 month in Car Nicobar island (90 15’ 3’’ and 90 7’ N latitudes and 920 42’ 30’’ and 920 50’E longitudes) and Camorta, Nancowry and Trinket Islands (70 55’ and 80 15’ E latitude and 930 25’ and 930 35’N longitudes).

Data Product

The Indian Remote sensing satellite (IRS P6) (of Feb.1,2005) digital data of LISS IV sensor with a spatial resolution of 6m was used for the landuse study complemented by ENVISAT SAR data (of Jan 3,2005) with a spatial resolution of 12.5m. Ancillary data like survey of India (SOI) topographical maps on (1: 50,000 scale), Differential GPS data and ground truth information were also used for the analysis.

Methodology:

Study of post tsunami remotely sensed data was done followed by field investigations in select locations to obtain 4 types of thematic information.

Inundation map:

Post tsunami data FCC of IRS-P6 LISS IV was used to map the Inundated areas. The map was prepared using visual interpretation techniques after limited field checks.

Run up level measurements of 9 coastal locations in Car Nicobar, 3 in Camorta and 1 in Champion islands were made using Differential Global Positioning System (DGPS). GPS measurements were utilized for getting the latitude, longitude, and altitude of the locations as per the overall methodology suggested by ICMAM.

Shoreline change map:

Shore line boundaries from toposheets and post tsunami IRS images of the study area on 1:50,000 scale were overlaid using ERDAS and ARCGIS software to obtain the shore line changes.

Coastal Geomorphology Map:

Prevailing coastal geomorphic features were identified with the help of satellite images and toposheets and maps were generated after limited field verifications.

Landuse/Landcover map:

Pre-tsunami landuse/landcover pattern was compared with the post –tsunami landuse/landcover pattern and various changes were identified through the satellite imagery. Final maps were prepared after limited field checks.