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EO·Atlas / Topics / Methodologies / SAR backscatter imaging
Methodology ยท SAR processing

SAR backscatter imaging

Synthetic-aperture radar amplitude imaging: measures the surface normalized radar cross-section (sigma-nought) at high spatial resolution, day-night and cloud-independent. The base SAR sensing method underlying ocean wind retrieval, wave-mode spectra, flood mapping, and change detection.

How it works

SAR backscatter imaging is the base active-radar method for all-weather surface imaging. It uses a synthetic-aperture radar payload to form calibrated amplitude images of surface backscatter at metre-to-tens-of-metres scale, independent of daylight and most cloud conditions.[1] It serves flooding, sea ice, oil spill screening, maritime surveillance, and the downstream SAR wind and wave methods that start from SAR image products.

The method needs radiometric calibration, incidence-angle metadata, polarisation metadata, and enough antenna, power, downlink, and processing margin for imaging modes. Interpretation fails when geometry dominates the target signal: layover, shadow, foreshortening, speckle, wind roughening, wet-surface effects, and incidence-angle variation can all look like real surface change unless the product is terrain-corrected and normalised.

Demonstrated implementations include Sentinel-1 C-SAR, ALOS-2 PALSAR-2, and ICEYE X-band SAR. C-SAR provides C-band SAR modes including Interferometric Wide swath imaging at 250 km swath and 5 x 20 m ground resolution.[1] PALSAR-2 adds L-band SAR with spotlight, stripmap, and ScanSAR modes plus single, dual, compact, and full-polarisation options.[2] ICEYE provides X-band SAR imaging modes for repeat commercial monitoring, with sub-metre tasking modes and day-night, all-weather operation.[3]

Topics this serves
Topic
Fit
Ocean surface windsfirst choice
Sea statefirst choice
Wind energy sitingfirst choice
Economic activity intelligencesuitable
Snow coversuitable

C-band SAR backscatter detects wet snow through cloud and at night, which tracks snowmelt extent; the Copernicus Sentinel-1 wet snow product is the operational example.

Ocean currentsadequate

SAR ocean products can provide local ocean surface velocity context, but the canonical row is broader SAR backscatter rather than a Doppler-current method.

Existing implementations
Demonstrated
Capable, undemonstrated
Related methodologies
  • InSAR - surface deformation

    Measures millimetre-scale ground surface displacement by comparing phase differences between repeat SAR passes; good for subsidence, earthquake deformation, and volcanic monitoring. Single-pass interferometry from a SAR pair also measures topographic height and underlies global digital elevation models such as Copernicus DEM.

  • Polarimetric SAR - target decomposition

    Decomposes backscatter into scattering mechanisms (surface, double-bounce, volume) using multi-polarisation data; good for forest structure estimation, urban mapping, and soil moisture retrieval.

  • Radar scatterometry

    Real-aperture radar that measures normalized radar cross-section from multiple azimuth angles to retrieve ocean surface wind vectors (speed and direction) over wide swaths at ~12-25 km resolution. Distinct from SAR: non-imaging, coarse-resolution, optimised for global daily wind fields.

Sources
Methodology

Edited from public sources by SpectraWorks editorial. See the data dictionary for field definitions.

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SAR backscatter imaging. EO-Atlas, SpectraWorks B.V. https://eo-atlas.org/topics/methodologies/sar-backscatter (CC BY 4.0)

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@misc{eoatlas:topics:methodologies:sar-backscatter,
  title = {SAR backscatter imaging},
  author = {{EO-Atlas}},
  publisher = {SpectraWorks B.V.},
  note = {CC BY 4.0},
  url = {https://eo-atlas.org/topics/methodologies/sar-backscatter}
}