Sentinel 1

Sentinel 1 is a imaging RADAR mission consisting of a pair of active satellites: Sentinel-1A and Sentinel-1B, operated by the European Space Agency (ESA). Sentinel 1 has initiated the operational phase of Copernicus – the largest European Earth observation program.

Sentinel 1 satellite

After a seven-year development period led by ESA and Airbus DS, the Sentinel-1A radar satellite was launched on April 3, 2014 with a Russian Soyuz launcher from the European Spaceport Kourou in French Guiana. The identical Sentinel-1B satellite arrived in space two years later, on April 25, 2016. Additionally, Sentinel-1C and 1D are in development with launch dates to be determined.

The main instrument is an imaging C-band SAR (Synthetic Aperture RADAR), consisting of a 12.30 x 0.90 m main antenna composed of 560 single antennas coupled together. Thus, unlike Sentinel 2 ​​or Landsat 8, Sentinel 1 works in the electromagnetic domain of microwaves. It actively emits elecromagnetic energy, which has a wavelength of 5.5 cm. The emitted radar rays penetrate through vegetation to the ground. As a result, changes in the surface in the centimeter and even in the millimeter range can be perceived. For a more detailed description of how SAR works generally, read SAR Basics.

Sentinel 1 serves a wide range of environmental, transport, economic and security applications. The focus is on ice observation in polar regions, volcanic activity, earthquakes, landslides, floods, detection of subsidence and elevations as well as the observation of sea surfaces to detect issues caused by sea ice and oil spills at an early stage. Furthermore, the satellites are designed to support disaster management in cases of emergency: Wherever up-to-the-minute information is needed, image data can be made available within 60 minutes.
Sentinel 1 has four different observation modes, allowing them to respond to those needs:

  • Stripmap (SM): monitor small-scale events upon requests
  • Interferometric Wide Swath (IW): primary operation mode for most applications over land
  • Extra-Wide Swath (EW): large-scale observation of marine areas
  • Wave (WV): primary operational mode over open ocean

According to the ESA Operation Plan the following applications can be mapped to these modes:

Arctic and sea-ice
Open ocean ship surveillance
Oil pollution monitoring
Marine winds
Urban deformation mapping
Flood monitoring
Earthquake analysis
Landslide and volcano monitoring

Each acquisition mode has different geometrical and therefore different temporal resolution characteristics:

  • SM: ~ 5 x 5 m
  • IW: ~ 5 x 20 m
  • EW: ~ 25 x 100 m
  • WV: ~ 5 x 20 m
  • SM, IW, EW: single (VV or HH) or dual polarization (VV+VH or HH+HV)
  • WV: single (VV or HH)
  • 16 bits per pixel (65,536 grey levels)
  • accuracy: 1.0 dB
  • Stability 1.0 dB
  • SM: 80 km swath width
  • IW: 250 km swath width
  • EW: 400 km swath width
  • WV: 20 km x 20 km scenes
  • orbit height: 693 km

Data Products

Just like Sentinel 2 data, Sentinel 1 ships its data in a zipped “SAFE” container format wrapping image data and product metadata in a specific folder structure. Do not alter this folder structure or any file names to ensure that image data and auxiliary information can be imported correctly. You do not need to unzip the file! The SNAP-software is able to read the file zipped.

Sentinel-1 data products which are generated by the Payload Data Ground Segment (PDGS) operationally are distributed at three levels of processing:

  • Level-0: compressed and unfocused SAR raw data, basis for all other high level products
  • Level-1: baseline product intended for most data users
  • Level-2: geolocated wind, wave and currents products derived from Level-1

For most applications, you should focus on Level-1 data. Additionally, Level-1 products can be one of two product types:

  • Single Look Complex (SLC) products are represented by a complex (I and Q) magnitude value and therefore contains both amplitude and phase information
  • Ground Range Detected (GRD) products consist of focused SAR data that has been detected, multi-looked and projected to ground range using an Earth ellipsoid model

A more comprehensive explanation of data product is given in the Sentinel 1 user guide.