Why Indian satellites did not observe the tsunami
INDIA CURRENTLY has 14 operational satellites orbiting the earth. Of these, eight are geostationary satellites and six are remote sensing satellites. Geostationary satellites, as the name indicates, seem fixed to one point as they orbit the earth once every 24 hours synchronising with the earth's rotation.
Altitude factor
Geostationary satellites would have been ideal to observe and warn about an approaching tsunami. However, to remain fixed to a place relative to the earth, the altitude of a geostationary satellite needs to be 36,000 km from the earth.
Can geostationary satellites be placed at lower altitudes that will enable them to pick up tsunami waves as they move in the deep sea? Geostationary satellites cannot be placed at lower altitudes. What velocity a satellite will have at a particular altitude or what altitude is required for a particular predetermined velocity is already fixed. These cannot be changed. In other words, a satellite will never be geostationary if it is at a lower altitude.
Moreover, geostationary satellites are put in orbit for communication and broadcasting purposes. These satellites are also used for meteorological purposes though. The cameras that these satellites carry (for meteorological purposes) have a resolution of 2 sq km in visible light and 8 sq km in infrared wavelength.
Cameras meant to monitor cloud formation and cyclone movement have a resolution of only 1 sq km. Hence the low resolution will not be able to pick up tsunami waves moving in the deep sea.
More so as the tsunami wave height in the deep sea is in the order of only a few centimetres. Remote sensing satellites orbit at 700-900 km from the earth's surface. These satellites do not remain fixed to a position (relative to the earth) as they are in a polar sun-synchronous orbit.
These satellites take just one hundred minutes to complete one orbit. Since the earth rotates, the satellite takes 22 days to come over the same region.
Resolution problem
Though these satellites have cameras with resolution starting from one metre and 5.6 metres in black and white (monochromatic) and 23 and 36 metres in colour (multispectral), they can at most identify and distinguish between land and water body but cannot provide details about wave height.
The same is the case with an ocean satellite that monitors ocean biota. Moreover, the cameras on board this satellite cannot penetrate cloud cover.
By Our Special Correspondent in Chennai
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