USGS EROS Archive - Radar - Synthetic Aperture Radar (SAR) Processing System

Science Center Objects

One of the most fundamental characteristics of a SAR system is its frequency (or frequencies) of operation (i.e., the frequency of the radar electromagnetic pulse it emits and receives); radar frequencies range from 3 MHz to 300 GHz.

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Synthetic Aperture Radar (SAR)

Christchurch, New Zealand (2010)

(Public domain.)


Synthetic-aperture radar (SAR) remote sensing is usually implemented by mounting, on a moving platform such as an aircraft or spacecraft, a single beam-forming antenna from which a target scene is repeatedly illuminated with pulses of microwaves at wavelengths anywhere from a meter down to millimeters. The many echo waveforms received successively at the different antenna positions are coherently detected and stored and then post-processed together to resolve elements in an image of the target region. SAR resolution is approximately equal to one-half the length of the actual (real) antenna and does not depend on platform altitude (distance). High range resolution is achieved through pulse compression techniques. Signal processing uses magnitude and phase of the received signals over successive pulses from elements of a synthetic aperture to create an image. As the line of sight direction changes along the radar platform trajectory, a synthetic aperture is produced by signal processing that has the effect of lengthening the antenna.

In general the larger the antenna, the more unique information you can obtain about a particular viewed object. With more information, you can create a better image of that object (improved resolution). It's prohibitively expensive to place very large radar antennas in space, so researchers found another way to obtain fine resolution data. They use the spacecraft's motion and advanced signal processing techniques to simulate a larger antenna.

SAR's ability to pass relatively unaffected through clouds, illuminate the Earth's surface with its own signals, and precisely measure distances makes it especially useful for the following applications:

  • Sea ice monitoring
  • Cartography
  • Surface deformation detection
  • Glacier monitoring
  • Crop production forecasting
  • Forest cover mapping
  • Ocean wave spectra
  • Urban planning
  • Coastal surveillance (erosion)
  • Monitoring disasters such as forest fires, floods, volcanic eruptions, and oil spills

Past and present research projects include: mapping the Antarctic continent; mapping the Amazon rainforest; using interferometric analysis for predicting or analyzing earthquakes and volcanic activity; and generating "Arctic Snapshots" of the Arctic ice extent.

Definition of SAR Radar Frequency Bands (Evans, 1995)

Definition of SAR Radar Frequency Bands (Evans, 1995)

(Public domain.)

Principles of Synthetic Aperture Radar

(Public domain.)

Additional information

Access Data

EarthExplorer can be used to search, preview, and download SAR Processing System data. The collection is located under the Radar category.