What is remote sensing?

Remote sensing is the  use of electromagnetic radiation to collect images and data  about the earth’s surface. With this technology, the information is collected by sensors that are far from the object or the analyzed area.

The material collected through remote sensing is quite accurate and authentic. Therefore, it is a reliable source for building detailed maps or studies.

This technology is used for many purposes, such as observing Earth features, natural phenomena, weather events, and urban growth.

Typically, the sensors that collect the data are carried by satellites, planes, and drones, but they can also be carried by any other means, such as cars or people. A satellite that takes images of the Earth is one of the best-known examples of remote sensing.

How does detection work?

The operation of remote sensing depends on three basic elements:

  1. observed object/area;
  2. Electromagnetic radiation (EMR): waves or particles that move at the speed of light;
  3. sensor: which measures the intensity of radiation.

To collect the information, the satellite uses solar radiation reflected by the Earth’s surface, which is captured by the remote sensor.

The sensors detect radiation at different wavelengths, much of which is invisible to the naked eye. Once detected, they turn into visible colors.

Then, the data collected by the sensor is transmitted to a central that collects, organizes and stores the information, such as the GIS, the Geographic Information System (or GIS –  Geographic Information System  ).

In Brazil, much of the data collected by remote sensing is used by INPE (National Institute for Space Research) and INMET (National Institute of Meteorology).

What are the types of remote sensing?

Sensors are divided into two types, depending on the radiation source they use: passive or active.

  • passive sensors  : they are the sensors that use external electromagnetic radiation, from sunlight;
  • Active sensors  : These sensors have their own radiation source, not depending on external radiation.

Passive sensors use their own radiation source (white arrows) and passive sensors use external radiation (yellow arrows).

Image Collection Levels

In general, the images collected by the sensors are on a small scale and, therefore, large areas can be observed in a short time.

Depending on the level at which the sensor is placed, the captured images may have more or less detail. The biggest difference between the levels is the size of the surface you scan (based on the distance between the area and the sensor).

There are three levels of data collection:

  • ground  : These are the images collected at near ground level, collected by people (handheld sensors) or by vehicles. Because it is so close to the ground, this type of detection is only able to observe small areas, but it is able to obtain more details.
  • Aerial  – In aerial sensing, sensors are attached to planes or drones, which record images of the earth’s surface.
  • orbital  : they are the sensors connected to artificial satellites, which are farthest from the Earth. Their greatest advantage is the great extension that they can observe. Depending on the type of technology used, they may be able to reveal more or less detail of the area.

What is remote sensing for?

Remote sensing technology has numerous functions, since the system can be used to observe many types of surfaces, collecting images that will be transformed into data. Today, one of the most widely used remote sensing techniques is the satellite, which orbits the Earth.

Due to its many applications, remote sensing is one of the most widely used instruments in geotechnology, an area that uses different technologies to collect, organize and analyze geographic data.

The  main uses  of remote sensing are:

  • creation of maps with varied data (cartography): geography, topography, hydrography, relief, vegetation, among others;
  • observation of the use of natural resources;
  • create or update maps and GPS in real time;
  • observation of climatic changes and prediction of meteorological phenomena;
  • monitor the growth of cities;
  • data collection for urban planning;
  • measure ocean levels;
  • control of deforested areas;
  • observation of areas used in agriculture.

Image of the Earth captured by a satellite in orbit of the planet.

How did remote sensing come about?

Remote sensing technology emerged during World War I (1914-1918), when aerial photography (aerophotogrammetry) was used to recognize targets and facilitate the planning of military operations.

A few decades later, beginning in the 1960s, remote sensing began to be used as we know it today, to collect images and information.

During the Cold War (1947-1991), the use of remote sensing grew a lot and was used by the United States and the Soviet Union.

The first Earth observation satellite was sent into space by NASA in 1972, it was called LANDSAT-1. The observation project still exists and the last satellite in this series, LANDSAT-8, was sent into space in 2013.

The first Brazilian observation satellite, SCD-1, was sent into space in 1993.

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