Earth observation satellite
Earth observation satellites or Earth remote sensing satellites are satellites specifically designed for Earth observation from orbit, similar to spy satellites but intended for non-military uses such as environmental monitoring, meteorology, map making etc. 
The first occurrence of satellite remote sensing can be dated to the launch of the first artificial satellite, Sputnik 1, by the Soviet Union on October 4, 1957. Sputnik 1 sent back radio signals, which scientists used to study the ionosphere.
NASA launched the first American satellite, Explorer 1, in January 31, 1958. The information sent back from its radiation detector led to the discovery of the Earth's Van Allen radiation belts.
The TIROS-1 spacecraft, launched on April 1, 1960 as part of NASA's TIROS (Television Infrared Observation Satellite) Program, sent back the first television footage of weather patterns to be taken from space.
, more than 150 Earth observation satellites were in orbit, recording data with both passive and active sensors and acquiring more than 10 terabits of data daily.
Space Race
On January 31, 1958, nearly four months after the launch of "Sputnik 1", von Braun and the United States successfully launched its first satellite on a four-stage Juno I rocket derived from the US Army's Redstone missile, at Cape Canaveral. The satellite "Explorer 1" was in mass. The payload of Explorer 1 weighed . It carried a micrometeorite gauge and a Geiger-Müller tube. It passed in and out of the Earth-encompassing radiation belt with its orbit, therefore saturating the tube's capacity and proving what Dr. James Van Allen, a space scientist at the University of Iowa, had theorized. The belt, named the Van Allen radiation belt, is a doughnut-shaped zone of high-level radiation intensity around the Earth above the magnetic equator. Van Allen was also the man who designed and built the satellite instrumentation of "Explorer 1". The satellite measured three phenomena: cosmic ray and radiation levels, the temperature in the spacecraft, and the frequency of collisions with micrometeorites. The satellite had no memory for data storage, therefore it had to transmit continuously. In March 1958 a second satellite was sent into orbit with augmented cosmic ray instruments.