Page 7 - Spec Tech Vol 1 Issue 06
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SPACE SENSORS
Image Credit: Manuel Campos-Taberner
An active sensor is a radar instrument used radio detection and ranging sensor to
for measuring signals transmitted by the measure backscattered microwave radiation,
sensor that were reflected, refracted or whereas LiDAR uses a light detection and
scattered by the Earth's surface or its ranging sensor to measure backscattered
atmosphere. Active sensors have their own light from an object. RADAR is used to build
source of light or illumination. In particular, it up a 2D representation of the object in
actively sends a pulse and measures the question and LiDAR is used to accurately
backscatter reflected to the sensor. But determine the distance of the object from
passive sensors measure reflected sunlight the spacecraft. Laser altimeters also use the
emitted from the sun. When the sun shines, principles of LiDAR detection, but these
passive sensors measure this energy. sensors are used to measure the height of a
Active sensors operate within the space object (satellite, platform or
microwave region of the electromagnetic spacecraft) above the Earth and for
spectrum; therefore, the emittance and determining the topography of the Earth’s
detection of reflected radiation can surface.
penetrate most atmospheres at long Scatterometers and sounder instruments are
distances, which is why many remote primarily used in and around Earth to
objects can be detected. Some of the most measure environmental conditions on Earth.
common active remote sensors include Scatterometers are primarily used over
laser altimeters, LiDAR, RADAR, ocean surfaces and use backscattered
scatterometers, and sounder instruments. microwave radiation to determine the speed
LiDAR and RADAR are both involved with and direction of the wind and provide a
measuring the distance between the detailed map. On the other hand, sound
spacecraft and a remote object—they are instruments measure the vertical distribution
both ranging instruments. Both work by of atmospheric precipitation, temperature,
measuring the backscattered radiation from humidity, and cloud composition around
a distant object, but RADAR uses an active Earth.
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