How do Earth and space surveillance satellites work?

The functioning of Earth and space observation satellites varies according to the type of orbit they describe, their size and the payload they carry on board, i.e. the type of optical instruments used, the imagery instruments, the satellite field of view, the orbital period, among others. 
There are two types of astronomical satellites: the first, those whose mission is focused on inspecting the entire sky, and the second, those that are only focused on observing a specific region of space. The payload of this type of satellites, called space observatories, has a powerful telescope similar to those we have on Earth, plus a number of sensors that can detect segments of the electromagnetic spectrum, including ultraviolet and infrared radiation, microwave and radio waves, as well as X-rays and gamma rays, which are impossible to detect with the instruments we have on the surface of the planet, because the atmosphere absorbs them and they do not reach us.

The data obtained by the satellite through the light receivers that have their sensors, are processed by special filters that have the satellite and reach the planet through large antennas arranged for this purpose. These are interpreted using certain algorithms and the images captured by the space telescope are revealed through a computer.

In the case of earth observation satellites, we find that they work in a similar way to astronomical telescopes. But unlike them, inside the payload is not a telescope but a series of cameras and sensors that evaluate different aspects within our planet. In addition, their orbits vary according to the observation function for which they were designed. For example, a meteorological satellite may be located in a geostationary orbit, in order to observe the evolution of the weather conditions of a specific region of the planet. In general, such satellites can have a constant field of view of an entire hemisphere. 

In contrast, most satellites that monitor specific aspects such as pollution levels, ocean levels, erosion, among others, are placed in closer orbits in order to obtain higher resolution images. These satellites can have active or passive sensors; this means, sensors that capture the sunlight that is reflected by the earth’s surface and those that have instruments that generate the radiation that they send to the earth and measure its refraction level on the surface.


This information reaches us through terrestrial receivers that capture the satellite signal and store it in large servers set up for this purpose. From there, the information is decoded through algorithms specially designed for its interpretation, generating images of high predictive value that can be used to solve ecological, economic, social and environmental problems.


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