Artificial Satellites of the Earth, Meteor and Meteor-Priroda

At first meteorological satellites were mainly used to obtain from space geometric images of clouds, ice and snow cover and to carry out their geographical referencing. This was done by using television frame systems. In modern space technology, the main instruments (radiometers and spectrometers) in use are based on the principle of spatial and spectral scanning, the essence of which is explained in Fig. 2.1 . Optomechanical scanning of a scene consists of stepby-step scanning of individual elements of the earth’s surface across the trajectory of the satellite by a special oscillating or rotating mirror. Electronic scanning is also used. The radiation received by the objective of the instrument through special filters, which separate it into the required bands, is focussed on to photodetectors. It is transformed into electric signals, which are coded and then transmitted to earth. Special calibrating signals (from standard emitters or from space) are introduced into the instruments, these permit us to obtain images and to measure element by element the distribution of the spectral intensities of radiation of different natural formations. The height of the orbit of the artificial satellite of the earth and the angle of oscillation of the mirror relative to the vertical determine the width of the strip of the earth’s surface to be scanned. Continuous line-by-line scanning of the earth is ensured through the motion of the satellite along its flight trajectory. Generally, several lines are simul-taneously surveyed in one step of scanning. Spectral scanning is ensured by special control filters (see Section 3 ).