Remote sensing is the process of obtaining information about any object or phenomenon without coming into physical contact with the object or phenomenon under investigation. 'Remote' means distance (here distant object) and 'sensing' means to sense (here acquisition of information). Thus the term 'remote sensing' literally means sensing from distance.

According to Ralph W. Kiefer and Thomas M. Lillesand,
Remote sensing is the science and art of obtaining information about an object, area or phenomenon through the analysis of data acquired by a device that is not in contact with the object, area or phenomenon under investigation.


Remote sensing is one of the most important and modern geographical techniques. In geographical studies, remote sensing basically works depending on the remote sensing satellites. The artificial satellites, which consist of remote sensors to observe Earth surface, atmosphere, or sometimes other celestial objects by detecting electromagnetic radiation, are called the remote sensing satellites.


Types of satellites

Each and every artificial satellites are remote sensing satellites, because they detect, record, and acquire information about objects and phenomenons without coming into physical contact. In recent times, there are lots of remote sensing satellites with various characteristics, which is orbiting the Earth or other celestial objects. The basic classification of satellites are mentioned through the following points.

1. Weather Satellites

As the name suggests, weather satellites provide us the information about the condition of weather for any location on the Earth. Meteorologists use the information and datasets from weather satellites and analyse them to provide us all the updates of weather.

Applications of the datasets provided by weather satellites include,
  1. To monitor the surface temperature of the Earth by detecting thermal radiation emitted from the Earth surface, and thus it helps to determine different temperature regions.
  2. The snow cover, movement of glaciers, etc. can easily be monitored by the obtained data from weather satellites.
  3. One of the special ability of some weather satellites is to detect the amount of water vapor in atmosphere. Some specific weather satellites consist the sensors which can detect it.
  4. Deforestation areas, regions suffering from drought, etc. can also be detected by the data acquired by weather satellites.

Some examples of weather satellites include GOES-16, GOES-17, TIROS-1, Suomi NPP, etc.


2. Astronomy Satellites

The satellites which orbit the Earth and observe other celestial objects and phenomenons, are called the astronomy satellites. These are mainly floating giant telescopes with powerful vision. The main functions of astronomy satellites include, mapping of different celestial objects like planetary surfaces and their moons, observing the black holes, meteorites, stars, exploring different planets, and many others.

Examples of astronomy satellites are IRAS, Astrosat, XMM-Newton, Hubble Space Telescope, etc.

3. Space Exploration Satellites

Space exploration satellites are those which probe deep into our solar system and explores numerous planetary bodies, moons, meteorite and lots of other celestial bodies and phenomena. These space exploration satellites provide detailed and many mysterious data of distant planets and celestial phenomena. Such as, the ring of Saturn ans its moons, Jupiter's moons, Olympus Mons of Mars, etc.

The main difference between the space exploration satellite and astronomy satellite is about its operating area. Space exploration satellites are not operated from the Earth orbit, rather it travels throughout the space or might orbit some planets other than Earth.

Galileo, Juno, Solar Orbiter, Hinode, Mars Global Surveyor, etc. are the space exploration Satellites.

4. Atmospheric Satellites

Atmospheric Satellites are created and launched into the Low Earth Orbit (LEO) to monitor Earth's atmosphere. Observing and acquiring data of atmospheric phenomena is the main activity of atmospheric satellite.

Alouette 1 was the first atmospheric satellite developed by Communications Research Centre Canada, launched on 29th September 1962, and deactivated in 1972. It was launched to carry forward the experiment about Ionosphere. It measured the density of electron in ionosphere by monitoring the timing between emission and back-scattering of radio waves. But it had not any recorder to store data, rather it used to consistently transmit data when it came into the range of the ground based receiving station.

Some other atmospheric satellites include CALIPSO, Aura, CloudSat, Upper Atmosphere Research Satellite, Orbiting Carbon Observatory-2, Nimbus 7, etc.


5. Navigation Satellites

The navigation satellites are mainly refers to a constellation of satellites which helps to navigate the direction and find out a location on the Earth surface. The principle that a navigation satellite constellation follows, the measurement of radio wave. The time and velocity, that a radio wave takes to travel between two points on the Earth surface, is measured precisely by the atomic clock in the satellite, and then it compute the distance between that two points by some automated techniques.

Indian Regional Navigation Satellite System  (IRNSS or NavIC), Global Navigation Satellite System (GNSS) are some well known constellation of navigation satellites.

6. Communication Satellites

Communication satellites are the most important and necessary for recent world. It is quite clear from the name that these satellites helps us to communicate even the longest distance in the world, whether by television, telephone or others. The communication satellites detect the high frequency radio telecommunication signals coming from a location on the Earth surface and transmit or relays them to another location or to its destination, through a transponder by creating a communication channel between the source (transmitter) and the destination (receiver).

The first ever telecommunication satellite was Telstar 1, launched by NASA on 10th July, 1962, and deactivated on 21st February, 1963. It was developed to built a telecommunication and live broadcast of television images between America and Europe.

These aforementioned are the main types of remote sensing satellites. Besides these, there are numerous satellites, like Satellites for search and rescue (e.g., LEOSAR or Low Earth Orbit Search and Rescue satellite, POES or Polar-orbiting Operational Environmental Satellite), Earth Observation Satellites (e.g., Cartosat-3) Reconnaissance Satellites (e.g., Zenit, Corona), and many more, developed for varieties of purposes.

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