K. K. Mohanty, Kanchan Maiti and Shailesh Nayak
Remote sensing images have been helpful in studying temporary water surges associated with earthquake
The killer earthquake on 26th January, 2001, the 51st Republic Day of India was accompanied by large scale discharge of subsurface (ground) water leading to reports of reemergence of the mythical Saraswati or Indus river. High revisit capabilities of IRS WiFs images have been helpful in studying the persistence of the released water in near real time. Three IRS images prior to the earthquake were analyzed along with a series of post earthquake images of the area to arrive at meaningful conclusion regarding the extent and period of the water surges. WiFs images are also found more useful to study synoptic contiguity of water discharges due to their larger swath as compared to LISS-III images.
The water surges are established to be a temporary phenomenon associated with the earthquake. WiFs images of 26 January, 2001 acquired barely 100 minutes after the quake shows emergence of many water sprouts and channels. There is a relative increase in volume of water in the WiFs image of 29th January (compared to 26th January) in some of the places. There after there has been a regular fall in the volume of water, which seem to have completely disappeared on 4th February and 13th February WiFs images. WiFs images of 23rd January, 2001, 20th January, 2001 and 7th January, 1999 were used to assess the pre-quake surface water scenario of the area. Generally, cracks can develop in soil after an earthquake and local ground water may come up along these cracks. This has been clearly demonstrated using IRS WiFs images that all these are completely temporary phenomena.
Fig. 1: WiFs FCC image of 26th January, 2001 depicting the location of sites used for detailed analysis. Site-2 images for a number of dates are shown subsequently.
Figure 1 shows the WiFs image of 26th January. The series of WiFs images of a number of dates both before and after the quake (namely 23rd January, 2001, 26th January 2001, 29th January 2001, and 4th January, 2001) for one of the three test sites is shown in Figure-2. All images are two-band false color composite with B4 (near infra red) band assigned to red plane and B3 (red) band being assigned to both green and blue planes of display. The water channels and sprouts appear in dark (black) color, while the dried up water channels appear in cyan as a result of an increase in red (B3) band gray count over near infra red (B4) band. The lower gray count of near infra red band is due to presence of moisture.
Fig. 2a: WiFs image of 23rd January, 2001 before the earth quake
Fig. 2b: WiFs image of 26th January, 2001 (First image after the earth quake). Some of water surges are marked using red arrows.
Fig. 2c: WiFs image of 29th January, 2001. This images shows maximum spread of water among all analyzed WiFs images. Red arrows indicate water channels.
Fig. 2d: WiFs image of 4th February, 2001 showing already dried up water channels.