Meteorological observations from satellites are at present the most avant-garde systems to collect data regarding the higher altitudes of the atmosphere, on a large scale. These recordings began in 1960, when the satellite TIROS.1 was launched. Experimental satellites, of the TIROS. NIMBUS, ESSA, A.T.S. and ITOS series contributed to improve the techniques and instrumentation progressively, and today satellite recordings are an indispensable and precious instrument to study the climate and for weather forecasts.
Meteorological satellites are subdivided into two main categories:
Heliosynchronous satellites orbiting at heights between 1,400-1,500 km over a polar orbit, that can cover the Earth’s surface in 12 hours. As these satellites operate in low orbits, they enable detailed observations of the Earth’s surface.
Geosynchronous or geostationary satellites orbiting at heights of approximately 36,000 km, which move at the same speed as the Earth’s rotation, thus remaining in an almost fixed position on the same point of the Earth’s surface, so that it is possible to obtain continuous images of the same zone, which has a radius of approximately 7,000 km. These satellites are used for short term weather forecasts. They are equipped with diverse probes for the radiations of different wavelengths, they can obtain images of the clouds in visible light, in the infrared band and with microwaves, and can record data on the vertical distribution of the temperatures and the humidity, on the distribution of the concentration of water vapour, of the cloud covering, precipitation and the principal systems of winds and currents, besides keeping the state of vegetable covering, and much more, under control. The satellites orbiting above the Equator can follow the formation and evolution of cyclones and tropical storms.
Geosynchronous satellites are positioned on an equatorial orbit, at approximately 72° longitudes distance from each other, and they forward signals to the stations generally every 30 minutes. Due to the Earth’s curvature, the detail of the images is greater for the latitude belts between 50°N and 50°S. Heliosynchronous satellites instead offer a greater detail of the Polar regions.