Spotlight is a SAR acquisition mode that allows increasing the illumination time of a particular area of interest by steering the antenna beam in azimuth direction. In this mode, the beam elevation is fixed, but the antenna is steered in azimuth direction, increasing therefore the length of the synthetic aperture. The rotation center of the antenna for steering is situated behind the scene at far range. The antenna footprint slides slightly forward over the scene in the azimuth direction during acquisition, but slower than in Stripmap mode, due to the antenna steering. The longest illumination time in azimuth direction results in an azimuth resolution that is highly enhanced compared to e.g. the Stripmap or the ScanSAR acquisition modes. However, this improvement is done to the detriment of the coverage. As for the other acquisition modes, the ground coverage and resolution depends on the considered sensor. For TerraSAR-X, a minimum coverage of 10 km in range and 5 km in azimuth direction is achieved in the Spotlight mode, with and azimuth resolution of about 1 m. The L-Band sensor Alos 2 also allow Spotlight acquisition mode, with a coverage of 25 km in both directions and a resolution of 1 m in azimuth direction, and down to 3 m in range direction.
Due to the very high resolution achieved in both directions, this acquisition mode is particularly usefull for urban area analysis as it allows for the detection of small objects. Therefore, Spotlight data are often used for the detection and recognition of man-made structures and objects, such as roads, buildings and even vehicles.