Today’s successful launch of the Megha-Tropiques satellite by ISRO takes my thoughts back to 1982. The first of the INSAT series of satellites, INSAT-1A, had been sent into geostationary orbit and I had just published my first research paper in satellite meteorology.

The paper was entitled “A conception of an equatorial orbiting meteorological satellite for the tropics”. I had Sant Prasad as my first coauthor and P. N. Khanna, who is now no more, was the second coauthor. I still remember that the referee had been reluctant to accept the paper for publication but had later relented with the condition that the paper be shortened to the minimum length possible. It was eventually published as a two-page letter to the editor (Mausam, 1982, vol. 33, no. 4, pp. 507-508).

In 1982, there were two distinct classes of meteorological satellites, polar orbiting and geostationary. Each of them had their advantages and disadvantages. The polar orbiting satellites obviously viewed the poles in every orbit, but they passed over any place on the equator only twice in 24 hours. Geostationary satellites were positioned relatively over a place on the equator at 36,000 km height from where they could scan a large part of the earth every 30 minutes. They were good for the tropics but could not see the poles.

My 1982 paper conceived of a different type of orbit that was a mix of the two. The orbit suggested was an equatorial orbit but the satellite was not to be at the geostationary height but at the height of a polar orbiter. This would enable the satellite to view the entire tropical belt during its revolution around the earth’s axis. Several such views of the entire tropical region would be generated during a 24-hour period. The north-south extent of the tropical belt and the repeat cycle could be designed as required just through a proper choice of the satellite height.

I still like this little paper of mine, not only because it was my first in satellite meteorology, but more so because in 1982 it was only an idea. I had no way of proving that it worked. It is only today, in 2011, that I have seen that it really works.

The MeghaTropiques satellite has been lauched by ISRO into an orbit that has a very low inclination of 20 degrees. It is not strictly an equatorial orbit but quite nearly so. The satellite is at a height of 866 km and the swath or the north-south extent of the coverage is 1700-2200 km wide. The period of revolution is 102 minutes and the repitivity is 6 times a day over a large part of the tropical belt and 4-5 times a day at higher latitudes. The satellite has four payloads that would help estimate oceanic winds, rainfall, temperature and humidity profiles, total water vapour, cloud liquid water, cloud ice, and radiation budget parameters, all from a common platform.


 

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