SENTINEL-1 carries a single C-band synthetic aperture radar instrument operating at a centre frequency of 5.405 GHz. It includes a right-looking active phased array antenna providing fast scanning in elevation and azimuth, data storage capacity of 1 410 Gb and 520 Mbit/s X-band downlink capacity.
The C-SAR instrument supports operation in dual polarisation (HH+HV, VV+VH) implemented through one transmit chain (switchable to H or V) and two parallel receive chains for H and V polarisation. Dual polarisation data is useful for land cover classification and sea-ice applications.
SENTINEL-1 operates in four exclusive acquisition modes:
Figure 1: SENTINEL-1 Modes
The primary conflict-free modes are IW over land and WV over open ocean.
Stripmap imaging mode is provided for continuity with ERS and Envisat missions. Stripmap provides coverage with a 5 m by 5 m resolution over a narrow swath width of 80 km. One of six imaging swaths can be selected by changing the beam incidence angle and the elevation beamwidth.
Interferometric Wide Swath Mode
The Interferometric Wide swath (IW) mode allows combining a large swath width (250 km) with a moderate geometric resolution (5 m by 20 m). The IW mode images three sub-swaths using Terrain Observation with Progressive Scans SAR (TOPSAR). With the TOPSAR technique, in addition to steering the beam in range as in SCANSAR, the beam is also electronically steered from backward to forward in the azimuth direction for each burst, avoiding scalloping and resulting in a higher quality image. Interferometry is ensured by sufficient overlap of the Doppler spectrum (in the azimuth domain) and the wave number spectrum (in the elevation domain). The TOPSAR technique ensures homogeneous image quality throughout the swath.
The IW mode is the default acquisition mode over land.
Extra Wide Swath Mode
The Extra Wide swath imaging mode is intended for maritime, ice and polar zone operational services where wide coverage and short revisit times are demanded. The EW mode works similarly to the IW mode employing a TOPSAR technique using five sub-swaths instead of three, resulting in a lower resolution (20 m by 40 m). The EW mode can also be used for interferometry as with the IW mode.
SENTINEL-1 Wave mode, in conjunction with global ocean wave models, can help determine the direction, wavelength and heights of waves on the open oceans.
Wave mode acquisitions are composed of stripmap imagettes of 20 km by 20 km, acquired alternately on two different incidence angles. Wave imagettes are acquired every 100 km, with imagettes on the same incidence angle separated by 200 km.