عنوان مقاله [English]
Over the past two decades, applications of satellite information have expanded along with advancements of remote sensing technology. Expansion of applications of satellite data, while in itself an important step toward fulfilment of needs of human being for information, requires researchers to produce information with spectral, spatial and radiometric characteristics that provide repetition of different temporal coverage. In this regard, some governments and private companies are making great efforts to continue their space plans until the year 2000, and to set advanced satellite systems on their orbits around the Earth. In this paper, the characteristics of four groups of satellites belonging to the early twenty-first century have been described and their capabilities examined.