A SAR satellite (Synthetic Aperture Radar) sends radar pulses obliquely to the ground and processes the echoes as it flies past, as if it were one enormous antenna. The result is an image that does not depend on daylight or cloud. How SAR works technically is covered in the EW Academy (§ 5.32).
- Strengths: always available; metal objects (vehicles, aircraft, ships) light up brightly; very small changes between two images can be measured (coherent change detection: vehicle tracks, disturbed soil).
- Weaknesses: the image is less intuitive (no colour, distortion from the oblique viewing angle); corners and metal decoys can mimic a real vehicle.
Commercial SAR constellations (such as ICEYE and Capella) now reach a resolution below one metre and can image the same area several times a day. The European Sentinel-1 provides coarser, but free, imagery.