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:
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the Global Ozone Monitoring Experiment (GOME) on ESA's ERS-2 satellite which operated between 1995 and 2011.
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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.
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the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) instrument onboard ESA's Envisat mission which operated between 2002 and 2012.
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the Ozone Monitoring Instrument (OMI) instrument onboard NASA's AURA spacecraft, operating since 2004 and still in service.
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the Tropospheric Ozone Monitoring (TROPOMI) instrument onboard ESA's SENTINEL-5P spacecraft expected to be launched in 2016.
As shown in table 1, 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 1hr) delivey 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 Table 1 .
GOME
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Whisk-broom (scanning)
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UV-VIS-NIR (240-790 nm)
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320 x 40
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Global
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1 ½ day
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1995-2011
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GOME-2
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Whisk-broom (scanning)
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UV-VIS-NIR (240-790 nm)
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80 x 40
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Global
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1 ½ day
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2006-present
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SCIAMACHY
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Whisk-broom (scanning)
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UV to SWIR (240-2400 nm)
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30 x 215
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Global
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6 days
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2002-2012
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OMI
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Push-broom (staring)
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UV-VIS (270-500 nm)
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13 x 24
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Global
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1 day
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2004-present
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TROPOMI
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Push-broom (staring)
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UV-VIS-NIR-SWIR (270 – 2385 nm)
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7 x 7
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Global
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1 day
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Launch scheduled in 2016
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SENTINEL-4/UVN
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Push-Broom (scanning)
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UV-VIS-NIR (305- 775 nm)
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8 x 8
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Europe + parts of North Africa and the Atlantic
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1 hour
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Launch scheduled in 2021
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Table 1: Main Characteristics of SENTINEL-4 and of its Heritage Instruments.