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Heritage Missions

The Sentinel-4 mission builds upon the heritage of a series of spectrometer instruments which have been or are currently measuring atmospheric properties since 1995; namely:

  • The Global Ozone Monitoring Experiment (GOME) on ESA's ERS-2 satellite which operated between 1995 and 2011.
  • The GOME-2 instrument on-board EUMETSAT's MetOp-A satellite, launched in 2006, still in service. A second GOME-2 is operating since 2012 on MetOp-B.
  • The SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) instrument onboard ESA's Envisat mission which operated between 2002 and 2012.
  • The Ozone Monitoring Instrument (OMI) instrument onboard NASA's AURA spacecraft, operating since 2004 and still in service.
  • The Tropospheric Ozone Monitoring (TROPOMI) instrument onboard ESA's Sentinel-5P spacecraft expected to be launched in 2016.

As shown in the table, among these five heritage instruments, the one which has the best global performances (e.g. spatial resolution, Signal-to-Noise Ratio, spectral coverage) is TROPOMI as it reunites several of the best characteristics of its predecessors, even going beyond them like for example an unprecedented on-ground spatial resolution of 7 x 7 km.

All Sentinel-4 heritage missions are passive backscatter spectrometers operating in Low Earth Orbits (LEO) which allow performing Earth global coverage measurements with a daily revisit time.

Sentinel-4 on the other hand will be the first imaging spectrometer instrument which will be embarked on-board a satellite in a geostationary (GEO) orbit.

The GEO orbit, although limiting the geographic coverage (for Sentinel-4 only to Europe and parts of North Africa and the Atlantic), will allow for the first time an extremely frequent (about 1hour) delivery of accurate atmospheric data: twenty to hundred times better than the LEO missions.

In terms of spatial sampling, Sentinel-4 will be roughly equivalent to Sentinel-5 and Sentinel-5P.

The wide spectral range covered by Sentinel-4 is narrower as compared to Sentinel-5 and Sentinel-5P, and has been chosen to cover the signatures of fast varying tropospheric constituents.

The main characteristics of the five heritage instruments are summarised in the table.

Main Characteristics of Sentinel-4 and of its Heritage Instruments
Instrument Technical Concept Spectral Range Spatial resolution (km x km) Earth Coverage Revisit time Operational
GOME Whisk-broom (scanning) UV-VIS-NIR (240-790 nm) 320 x 40 Global 1 ½ day 1995-2011
GOME-2 Whisk-broom (scanning) UV-VIS-NIR (240-790 nm) 80 x 40 Global 1 ½ day 2006-present
SCIAMACHY Whisk-broom (scanning) UV to SWIR (240-2400 nm) 30 x 215 Global 6 days 2002-2012
OMI Push-broom (staring) UV-VIS (270-500 nm) 13 x 24 Global 1 day 2004-present
TROPOMI Push-broom (staring) UV-VIS-NIR-SWIR (270 – 2385 nm) 7 x 7 Global 1 day Launch scheduled in 2016
Sentinel-4/UVN Push-Broom (scanning) UV-VIS-NIR (305- 775 nm) 8 x 8 Europe + parts of North Africa and the Atlantic 1 hour Launch scheduled  in 2021

 

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