Sentinel-5P is the first Copernicus mission dedicated to monitoring the Earth’s atmosphere, making regular measurements of trace gases and aerosols that affect the atmosphere and our climate. Its payload consists of the Tropospheric Monitoring Instrument (Tropomi), a spectrometer that is sensitive to a wide band of radiation from the ultraviolet (UV) to the infrared ends of the spectrum.

Sentinel-5P: mission timescale

  • Mission launch: 13 October 2017
  • End of commissioning phase: 30 April 2018
  • Start of routine mission operations: 5 March 2019
  • Mission duration: 7 years

There was a ‘ramp-up’ period between the end of the commissioning phase, when some data products started to become available, and the start of routine operations.

About the Sentinel-5P mission

Sentinel-5 Precursor (Sentinel-5P) was designed to reduce the gap in gathering atmospheric data, including pollutants, between the end of the Envisat mission in 2012 and the Sentinel-5 satellites, the first of which was planned for the 2020-2022 timeframe – hence the ‘Precursor’ label. The requirement for such a mission was related to the need for atmospheric data related to climate change monitoring.

Internal view of the Sentinel 5P satellite - Image copyright ESAATG medialab
Internal view of the Sentinel-5P satellite. © ESA / ATG medialab

About Sentinel-5P’s orbit

Sentinel-5P was launched on 13 October 2017 from the Plesetsk Cosmodrome in northern Russia into a sun-synchronous, low Earth orbit with a very high inclination (98.7 degrees). This orbit enables it to achieve almost complete coverage of the Earth so it can provide data on the global state of the atmosphere; it also means it always observes the same part of the atmosphere at the same time, which is better for comparing data from the same region.

The orbital cycle is 16 days, during which the satellite performs 227 orbits, taking 1 hour and 40 minutes per orbit. Each orbit generates around 140Gb of data, which is usually is downlinked once per orbit. However, if one downlink is missed for any reason, the spacecraft’s total storage space of 480Gb means the data can be stored until the next downlink period with no loss of data.

Sentinel-5P’s scientific payload

Tropomi instrument Image copyright Airbus Defence and Space
Tropomi instrument © Airbus Defence and Space

The Sentinel-5P payload consists of a single instrument, Tropomi, which is jointly funded by ESA and the Dutch Government. Tropomi is a ‘pushbroom’ spectrometer that is sensitive to a wide range of wavelengths: ultraviolet (UV), visible (VIS), near infrared (NIR) and short wavelength infrared (SWIR).

As the name indicates, the instrument, sweeps a swath over the Earth like a giant broom. This swath is approximately 2,600km wide and provides daily coverage of 95% of the surface of the Earth (latitudes between -7 and 7 degrees). The resolution of Tropomi (7km x 7km) is much higher than that of its predecessor, SCIAMACHY, which was a payload on Envisat (200km x 30km).

A spectrometer like Tropomi works by comparing light reflected by the atmosphere with direct sunlight. Each chemical in the atmosphere absorbs a unique set of specific wavelengths. By comparing the reflected light with direct sunlight, we can calculate which chemicals are present in the atmosphere and in what amounts.

Tropomi measures the abundance of key atmospheric components and pollutants including: ozone; nitrogen dioxide; carbon monoxide; sulphur dioxide; methane; formaldehyde; aerosols; and clouds. This list of chemicals is the reason Sentinel-5P is so important for the study of the atmosphere and all the processes that have an influence on the quality of air and climate change.

As always in science, much can be gained working as a team and Sentinel-5P is a good example of this. The Suomi National Polar-orbiting Partnership (Suomi NPP) satellite, a joint NASA/NOAA (US National Oceanic and Atmospheric Administration) mission, carries the Visible/Infrared Imager and Radiometer Suite (VIIRS) instrument, which can provide higher resolution cloud masks than those provided by Sentinel-5P. With this in mind, the orbit of Sentinel-5P has been carefully set to be similar to Suomi NPP, with Sentinel-5P trailing just a few minutes behind, allowing Sentinel-5P to use the higher quality cloud masks generated by Suomi NPP data. (The cloud masks and Sentinel-5P data need to coincide in time because cloud cover varies so quickly.)

Sentinel-5P data products

Sentinel-5P generates large amounts of data – around 2Tb of data per day. This is processed to generate the products that are relevant for climate and atmospheric studies, which are available at three different levels: Level 0, Level 1B and Level 2.

Level 0 consists of time-ordered raw data. This is very difficult to use as it requires detailed technical knowledge of Tropomi and the satellite itself, so is not publicly available.

Level 1B products consist of geo-located, corrected, top-of-the-atmosphere radiances in all spectral bands and solar irradiances. Level 2 products contain information on the column densities of ozone, sulphur dioxide, carbon monoxide, formaldehyde and methane; these are the ones used to generate the maps typically associated with news related to climate change.

Due to the time it takes to process the data and validate the final products, they are not available instantaneously. Instead, some are generated as quickly as 3 hours and others may take a few days, with the exception of two Level 2 products that can take up to 15 days to produce.

Climate studies using Sentinel-5P data

An instrument such as Tropomi is a valuable asset because it allows us to produce maps of the distribution of the main pollutants and some of the greenhouse gases in the atmosphere at unprecedented resolution. By performing daily measurements, we know exactly where they are and how their abundance evolves, helping us pinpoint their origin and evolution – vital for tackling climate change.

With Tropomi’s high resolution (compared with Envisat’s SCIAMACHY) we can see what is happening inside a big city in detail, such as the increasing amounts of pollutants due to, for example, the emissions of cars running on fossil fuels. As an example, with SCIAMACHY the Netherlands were covered by around 10 pixels; with Tropomi the same number of pixels cover Amsterdam alone.

Image showing the tropospheric nitrogen dioxide intensity over Europe with Tropomi data
Tropospheric nitrogen dioxide intensity (in 1015 molec/cm2) over Europe on 27 February 2019 using Sentinel-5P Tropomi data © Contains modified Copernicus data (2018), processed by ECMWF

Did you know?

In February 2020, observations from Sentinel-5P allowed scientists to detect a decrease in the levels of nitrogen dioxide over China, assumed to be due to restrictions in mobility to stop the propagation of COVID-19. A month later, the same trend was observed over some major cities in Europe.

The trend was later reversed, with data from February 2021 showing the situation in China and elsewhere back to what it was before the COVID-19 pandemic. Sentinel-5P therefore helps us understand how variances in human activity affect emissions of pollutants linked to climate change.

How RHEA is contributing to the Sentinel-5P mission

RHEA contributes to the Sentinel-5P mission with two staff providing post-launch support (PLS) services – we do this for each of the ESA-supported Sentinel missions: Sentinel-1, -2, -3 and -5P. We support the PLS function across all aspects of satellite performance monitoring and analysis during phase E2 (the ‘exploitation’ phase, which follows on from the commissioning phase) and related day-to-day support activities.

These are some of the functions RHEA’s team provides:

Diagram showing RHEA support activities for Sentinel 5P mission 870px

Main image: Artist’s impression of Sentinel-5P © ESA / ATG medialab