In the ScanSAR acquisition mode, the antenna beam is successively steered to different elevation angles. This results in adjacent, slightly overlapping stripes, or sub-swaths along the range direction, parallel to the azimuth direction, each stripe having a different incidence angle at its center. During antenna steering in elevation, transmitter and receiver are off. Therefore, each stripe is illuminated for a shorter time as for the StripMap mode, leading to a degradation of the azimuth resolution. However, ScanSAR allow a larger coverage in range direction than the other imaging modes. Each sub-swath is illuminated for a shorter time than in the Stripmap case. The timing is adjusted though, such that the time-varying antenna footprint repeat cyclically. Similar to the other acquisition modes, the achievable resolution and coverage of ScanSAR products depends on the considered sensor and its properties. For X-Band, e.g. for TerraSAR-X, a total swath width of 100 km in range direction can be achieved using four adjacent sub-swaths or, using a Wide ScanSAR mode with six adjacent sub-swaths, a swath width up to 270 km can be achieved. A Wide ScanSAR scene shows incidence angles ranging from 15.6° in near to 49° in far range. The azimuth resolution varies between 18.5 m and 40 m, for ScanSAR and WideScan SAR modes respectively. For the L-Band sensor ALOS-PALSAR 2, a swath width up to 40 km can be achieved, with incidence angles ranging from 8° to 70° and an azimuth resolution of 60 m. The ScanSAR mode is well suited for large-area monitoring, e.g. for sea ice or glacier monitoring, as well as for mapping large-scale disasters, such as oil slick, or areas devastated by forest fires. Using interferometry, topography mapping and deformation monitoring is also possible.
Compare and discuss different SAR acquisition modes
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