SyntheticApertureRadar

Synthetic Aperture Radar (SAR) is a form of radar used to create high-resolution two-dimensional images or three-dimensional reconstructions of landscapes. Operating in the microwave portion of the spectrum, SAR can image the Earth through clouds and at night, providing consistent data under varying weather and illumination conditions.

Principle and processing: A SAR system mounts on a moving platform such as an aircraft or satellite. It emits microwave pulses and records the backscattered echoes as the platform travels. By exploiting the Doppler effect across many positions, the radar synthesizes a much larger effective antenna aperture, yielding fine azimuth resolution. Range resolution is set by the transmitted pulse bandwidth, while azimuth resolution improves with the synthetic aperture through coherent processing of the received phase information.

Data characteristics and challenges: SAR data are typically complex-valued, containing amplitude and phase information that enables interferometry and polarimetry. Processing steps include range and azimuth compression, motion compensation, calibration, and speckle reduction. The imagery can exhibit geometric distortions such as layover, foreshortening, and shadow, and requires careful interpretation and correction in advanced applications.

Imaging modes and capabilities: SAR supports several modes, including stripmap, spotlight, and ScanSAR, which trade resolution for swath width. Advanced variants offer polarimetric (PolSAR) data and interferometric (InSAR) capabilities to measure surface height and deformation. Multi-look processing and time-series analyses enhance reliability for various observations.

Applications and platforms: SAR is widely used for earth observation, topographic mapping, monitoring land deformation, ice and ocean studies, forestry and agriculture, disaster response, and infrastructure monitoring. Spaceborne systems such as Sentinel-1, TerraSAR-X, and Radarsat-2, along with airborne SAR, provide diverse data for research and operational needs.