Acquisition modes

Last modified by Tuan Le on 2019/05/21 14:20

Index

  • Stripmap
  • Interferometric wide
  • Extra wide
  • Wave
Stripmap (SM) mode acquires data with an 80 km swath at slightly better than 5 m by 5 m spatial resolution (single look). The ground swath is illuminated by a continuous sequence of pulses while the antenna beam is pointing to a fixed azimuth angle and an approximately fixed off-nadir angle (this is subject to small variations because of roll steering). SM images have continuous along track image quality at an approximately constant incidence angle.
The Interferometric Wide (IW) swath mode is the main acquisition mode over land and satisfies the majority of service requirements. It acquires data with a 250 km swath at 5 m by 20 m spatial resolution (single look). IW mode captures 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 homogeneous image quality throughout the swath.
Similar to the IW mode, the Extra Wide (EW) swath mode employs the TOPSAR technique to acquire data over a wider area than for IW mode using five sub-swaths. EW mode acquires data over a 400 km swath at 20 m by 40 m spatial resolution. The EW mode is aimed primarily for use over sea-ice, polar zones and certain maritime areas, in particular for ice, oil spill monitoring and security services. Like IW, EW mode can also be used for interferometry since it shares the same characteristics for burst synchronisation, baseline and Doppler stability.
Sentinel-1 Wave mode is similar to ERS and Evnisat wave mode imaging but with improved spatial resolution, larger vignettes and a 'leap frog' acquisition pattern as illustrated in the figure below. WV acquisitions consist of several vignettes exclusively in either VV or HH polarisation, with each vignette processed as a separate image. WV mode products can contain any number of vignettes, potentially amounting to an entire data-take. Each vignette is contained in an independent image within the product.