Active Sensors

SIR-C Image of the Mississippi River Delta,Courtesy JPL

Active sensors are used in a different area of remote sensing; typically they give scientists an understanding of the structure of surface features.These sensors are radar and laser altimeters, imaging radars, and radar scatterometers.

The principle behind an active sensor is they broadcast a signal from the sensor and measure the energy reflected back to the sensor and the time of flight of the signal.

energy returned = backscatter coefficient * transmitted energy

The backscatter coefficient depends on the physical properties of the surface such as

  • surface roughness
  • variations in surface topography
  • physical properties of the surface
  • and water content.




This image of the San Francisco Bay was taken from an imaging radar flown onboard the Space Shuttle Endeavor in October 1994.

Active sensors allow scientists to gain information about the topography of the surface as well as information about oceanographic patterns. By using altimetry data, scientist can study the circulation and currents in the oceans.


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Last Modified: Thu, Jul 29, 1998
CSR/TSGC Team Web