Synthetic Apature Radar (SAR) Basics

This pages provides some resources and a brief overview of Synthetic Apature Radar (SAR) in the context of Sentinel 1 ARD.

NASA’s web page gives some great introductory information regarding SAR, including a brief overview of the role of wavelength and polarization.

Sentinel-1 uses C-band radar (5.405 GHz frequency or 5.55 cm wavelength) with the primary objectives including the mapping of glaciers, ice sheets, and sea ice, as well as land surface topography. Important secondary objectives include land cover monitoring, snow cover mapping, surface soil moisture retrevals, and ocean wave science, among many others! You can read more on the specific details of the Sentinel-1 mission, and its objectives, here.

Besides radar frequency, polarization is also an important aspect of SAR data. The polarization, or orientation of the radar wave, can give us important information regarding the properties of the target. Some applications using this polarimetric information include crop identification, soil moisture retrivals, geological mapping, shoreline detection, biomass estimation, ocean wave measurements, and much more. You can read about more polarization use cases here.

Radar waves can be polarized in either the horizontal or vertical direction, indicated by the letter H or V respectively. If a sensor emits and retrieves a radar signal in a single polarization, it will be noted as VV or HH. Additionally, the radar wave can be emited in one polarization and observed in the other, such as a wave emited in a vertical polarization but retrieved in the horizontal polarization. This type of observation is notated with VH (or HV in the inverse case).

Sentinel 1 provides single and dual polarization, however as this analysis ready data comes from level 1 Interferometric Wide swath (IW), only the VV and VH polarizations are retrieved. You can read more about S1 aquisition modes here.