Sentinel-4 is a European Earth observation mission developed to support the European Union Copernicus Programme for monitoring the Earth. It focuses on monitoring of trace gas concentrations and aerosols in the atmosphere to support operational services covering air-quality near-real time applications, air-quality protocol monitoring and climate protocol monitoring. The specific objective of Sentinel-4 is to support this with a high revisit time over Europe.
The Sentinel-5 precursor, Sentinel-4 and Sentinel-5 represent elements complementary of a constellation intended to serve the needs of Copernicus Atmosphere Monitoring Service (CAMS). Sentinel-4 will consist of two instruments integrated onboard a Meteosat Third Generation Sounder (MTG-S) satellite to observe primarily the tropospheric composition of the Earth's atmosphere.
The data will be gathered and made available to the Copernicus program with the aim of contributing to air quality applications such as with the Copernicus Atmosphere Services as well as the air quality monitoring over the regions of Europe and Northern Africa.
As with other aspects of the Copernicus programme, the Sentinel-4 initiative is funded mostly through the EU and the technical design and development has been put under responsibility of the European Space Agency (ESA).
The mission objective, as stated from the official European Space Agency website, is to observe the amount of particulate matter in the air above Europe and North Africa. They seek to monitor impacting compounds such as O3 (Ozone), NO2 (Nitrogen dioxide), SO2 (Sulfur dioxide), HCHO (Formaldehyde), and more. The information gathered from the satellite will then be used to instill European laws in their own benefit.
For the detection and measurement of atmospheric characteristics, two payload instruments have been designed; the Ultra-Violet and Near Infra-Red Multispectral Spectrometer (S4 UVN) and the Infra Red Sounder (S4 IRS). The two instruments will be embarked on two Eumetsat Meteosat Third Generation Sounder (MTG-S) satellites due to be launched in 2024 and 2034.
Satellite platform
Meteosat Third Generation (MTG)
As the name suggests, Meteosat Third Generation is the third generation of meteorological satellites and is developed by Thales Alenia Space (TAS) under the responsibility of Eumetsat and ESA. It is the ‘next generation’ for numerical weather predication and nowcasting. The unprecedented high-resolution and profiling technology will yield a vast improvement in weather forecasting reliability for the medium and long term. Eumetsat will head up the operations of the programme and will also ensure provision of meteorological data and services to European as well as International users and improved imaging capability to the scientific community.
“The objective of the MTG system is to provide continuous high-resolution observation data and geophysical parameters of the Earth system derived from direct measurements from the radiation it emits and reflects using satellite-based sensors from a geostationary orbit. Thanks to advances in technology, MTG, compared to the current MSG system, will also provide a more powerful tool by contributing significant improvements to the existing service with an improved imagery mission and by introducing new sounding and lightning missions from a geostationary orbit” – a quote from the MTG publication produced and published by OHB System AG.
Meteosat Third Generation Sounder (MTG-S) Satellite
The MTG-S satellites make up 2 of the 6 satellites in the MTG satellite fleet. The MTG-S satellites are mounted on common 3-axis stabilised platforms and are dedicated to sounding applications, including the integration of the S4 UVN an IRS instrument payloads. MTG-S1 is currently planned to be launched in 2024, and MTG-S2 in 2034.
Instruments
S4 UVN Multispectral Spectrometer
The UVN multispectral spectrometer is a hyperspectral spectrometer operating with spectral bands within the solar reflectance spectrum. For the UVVIS part the range is between 305 nm to 500 nm with a resolution of 0.5 nm and for the NIR part the range is 750 nm to 775 nm with a resolution of 0.12 nm. These bands work in combination with low polarization sensitivity and high radiometric accuracy. The instrument design allows for an east–west scan revisit time of approximately 1 hour, covering most of Europe and Northern Africa. With around 570 spatial samples in the east–west spatial dimension a corresponding scan rate (spatial sample rate) of approximately 8 km every 6 seconds is possible (around 1.3 km/s).