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Synthetic Aperture Radar

What is Synthetic Aperture Radar?

A Synthetic Aperture Radar (SAR), is a airborne or spaceborne sidelooking radar system which utilizes the flight path of the platform to simulate an extremely large antenna or aperture electronically, and that generates high-resolution remote sensing imagery.

SAR uses the motion of the radar antenna over a target region to provide finer spatial resolution than conventional stationary beam-scanning radars.

The spatial resolution of radar data is directly related to the ratio of the sensor wavelength to the length of the sensor’s antenna.


  • SAR is a Side-looking radar system which makes a high-resolution images of the Earth’s surface.
  • Continuous strips of the ground surface are “illuminated” to one side of the flight direction.
  • Signal is recorded and Digital signal processing techniques in the ground are used to focus the image and obtain a higher resolution images.
  • The across-track distance is called the “Range”
  • The along-track distance is called the “Azimuth”.

How Does SAR Work?

A SAR is an active sensor that first transmits microwave signals and then receives back the signals that are returned, or backscattered, from the Earth’s surface.

The SAR works similar of a phased array, but contrary of a large number of the parallel antenna elements of a phased array, SAR uses one antenna in time-multiplex.

SAR Resolution

SAR has two resolutions :

  1. Range Resolution- is achieved by using Pulse compression technique.
  2. Azimuth Resolution- is achieved by using Synthetic aperture concept.

SAR Bands

BandFrequencyWavelengthTypical Application
X8–12 GHz3.8–2.4 cmHigh resolution SAR (urban monitoring, ice and snow, little penetration into vegetation cover; fast coherence decay in vegetated areas)
C4–8 GHz7.5–3.8 cmSAR Workhorse (global mapping; change detection; monitoring of areas with low to moderate penetration; higher coherence)
S2–4 GHz15–7.5 cmSAR Earth observation (agriculture monitoring, NISAR will carry an S-band channel; expends C-band applications to higher vegetation density)
L1–2 GHz30–15 cmMedium resolution SAR (geophysical monitoring; biomass and vegetation mapping; high penetration, InSAR)
P0.3–1 GHz100–30 cmBiomass. First p-band spaceborne SAR will be launched ~2020; vegetation mapping and assessment. Experimental SAR.

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