SARradar

SAR radar, short for synthetic aperture radar, is an active remote sensing system that produces high-resolution radar images by leveraging the motion of the platform carrying the antenna. It transmits microwave pulses and records the backscattered signals, with the phase information preserved to enable coherent imaging. Unlike optical sensors, SAR can operate in day or night conditions and through cloud cover or precipitation.

The core principle is the synthetic aperture. As the platform moves, successive measurements along the flight path are combined to create a virtual antenna longer than the physical antenna, dramatically improving azimuth (along-track) resolution. Range resolution is determined by the transmitted pulse bandwidth, while azimuth resolution depends on the processing of Doppler history. The resulting images are complex-valued, containing amplitude and phase that enable radiometric analysis and interferometric measurements.

Data from SAR systems can be processed in several ways. Standard SAR provides detailed structural information about surfaces. Interferometric SAR (InSAR) compares phase from two or more acquisitions to measure ground deformation, topography, or subsidence. Polarimetric SAR (PolSAR) exploits multiple polarization channels to improve discrimination of surface types. Multi-pass acquisitions enable change detection and time-series analysis.

Platforms and frequency bands vary. Spaceborne systems include C-band sensors like Sentinel-1, L- or C-band systems for various missions, and X-band satellites such as TerraSAR-X. Airborne systems offer flexible coverage and higher-resolution options. Typical ground resolutions range from a few meters to tens of meters, depending on mode and wavelength.

Applications span land mapping, vegetation monitoring, urban planning, disaster response, ice and ocean monitoring, and environmental research. Limitations include speckle noise, data volume, calibration requirements, and interpretation challenges, particularly in heterogeneous terrain.