The Interferometric Wide Swath Mode is a particular acquisition mode of the C-Band satellites Sentinel-1 which implements the TOPS (Terrain Observation with Progressive Scan) method. It combines an antenna steering in elevation, as in ScanSAR mode, with a counterrotation of the antenna beam from backward to forward steering, opposite to the steering happening in Spotlight mode. The data is acquired in bursts by cyclically switching the antenna beam between multiple adjacent sub-swaths.
This opposite steering direction of the antenna along the azimuth leads to a shorter target illumination and induces a decrease of the resolution, but a cyclically continuous coverage in azimuth direction. The principal difference to the other acquisition modes is that this acquisition mode implies a shrinking of the antenna footprint virtually to a ground target instead of slicing it to retrieve the target.
The Interferometric Wide Swath Mode (IW) was originally designed to solve Signal-to-Noise heterogeneities and azimuth ambiguities appearing in the ScanSAR mode.
For Sentinel-1, the IW mode provides a coverage of 250 km in range direction with an azimuth resolution of 20 m and incidence angles ranging from 29.1° in near to 46° in far range.
Standard Single Look Complex Sentinel- 1 IW products contain three sub-swaths in range direction, with nine burts in azimuth direction.
The IW mode is the standard acquisition mode of the Sentinel-1 C-Band satellites and is acquired continuously over all land surfaces. The application are very diverse, ranging from agriculture and forestry to urban deformation monitoring and ship surveillance.
Similar to the IW mode, the Extra Wide Swath Mode (EW) of Sentinel-1 uses the same TOPS technique, but covers even wider areas up to 400 km in range direction, to the detriment of the resolution which decreases to 40 m. The EW Mode principally finds application in maritime applications such as artic and sea-ice monitoring, analyses of marine winds and oil pollution monitoring.