Context and Goals of Sentinel-5P and TROPOMI

News - 10 October 2017

The TROPOMI instrument launches this Friday on board Sentinel-5 Precursor payload. But why is TROPOMI that important for the atmospheric composition scientific community? And why is it a “precursor”?

The main context is the Copernicus programme, coordinated and managed by the European Union: it aims at developing European information services based on satellite Earth Observation and in situ data. The dedicated satellites are the so-called Sentinel missions, which must deliver near-real time information on a global level which can also be used for local and regional needs.

TROPOMI and Sentinel-5P are part of the series of Sentinel satellites, which are central of the Copernicus Program.

While Sentinels 1, 2, and 3 are dedicated to the surface (ocean and land), Sentinel-4 (geostationary platform) and 5 (low Earth orbit) are specifically designed for monitoring our atmosphere and its changes. Sentinel-4 will be a Geostationary platform focused on Europe with a fast (hourly) revisit time. Sentinel-5 will be a polar-orbiting with a daily global revisit frequency. Both are designed for a very high spatial resolution.

Where do TROPOMI and Sentinel-5P fit into this? The main reason: Sentinel-4 & 5 are not scheduled to be launched until at least 2020, meaning that without it we run the risk of a large gap in atmospheric observations.

In the last 6 years, 2 key European satellite missions devoted to air quality died: GOME on-board ERS-2 and SCIAMACHY on-board ENVISAT. Other sensors such as GOME-2, on-board the MetOp series, keep measuring air quality but in the morning (lower signal compared to the afternoon) and with a coarse spatial resolution (80 x 40 km2).

Prof. Dr. Pieternel Levelt is head of the R&D satellite department at KNMI & Professor at GRS TU Delft. Here she stands with a model of Sentinel-5P featuring TROPOMI.

Only OMI today delivers key information on our air quality (e.g. toxic pollutants such as NO2 – Nitrogen dioxide – and aerosol particles), and the O3 (ozone) layer in the afternoon (thus optimizing high signal acquired) at a lower resolution: 13 x 24 km2. OMI is a successful Dutch-Finnish mission, on-board the American NASA Aura platform, acknowledged by key experts and authorities on our air quality and atmospheric changes. It is led by Prof. Dr. Pieternel Levelt (head of the R&D satellite department at KNMI and Professor at GRS TU Delft) But, in spite of its still remarkable good quality, its advanced age (13 years old!) is far beyond its initial expected lifetime.

10-year average (2005-2014) NO2 – Nitrogen Dioxide (toxic gas released by fossil fuel activities) as observed by OMI in the troposphere (Levelt et al., 2012)

There is then an urgent need to anticipate the potential gap between GOME-SCIAMACHY-OMI satellites, and the future Sentinel-5. Such a need inspired the idea of Sentinel-5 Precursor, a gap-filler and a preparatory programme covering products and applications for Sentinel-5. Dutch national expertise and their studies have been key elements to lead to TROPOMI.

The main objectives of TROPOMI are focused on monitoring our troposphere (i.e. the lower part of the atmosphere where humans live) by measuring key toxic gases affecting our air quality (NO2, SO2, HCHO, CO, O3), climate forcing via the powerful green-house gas methane (CH4), aerosol particles, and the upper Ozone layer. Compared to OMI, TROPOMI will map cities with a finer resolution (7 x 3 km2), a lower instrument noise, and measure new key gases (e.g. CO & CH4).

With its global coverage and open data policy, the mission is an essential contribution for providing critical information to services and decision makers to improve the life and atmospheric composition of European citizens, and our knowledge of important chemical and dynamical processes in the atmosphere. The daily global observations will be used for improving air quality forecasts as well as for monitoring the concentrations of atmospheric constituents. Trend monitoring is very important to verify that policies implemented to control emissions to the atmosphere are effective. In addition, TROPOMI will also contribute to services on volcanic ash for aviation safety, warnings for high levels of UV radiation that can cause skin damage, and to numerical weather prediction.

OMI-TROPOMI-Sentinel-5: a long-term heritage for monitoring, managing and protecting our unique air!

More information in Veefkind et al., 2012:
Veefkind, J. P., Aben, E. A. A., McMullan, K., Forster, H., de Vries, J., Otter, G., … Visser, H.: TROPOMI on the ESA Sentinel-5 Precursor: A GMES mission for global observations of the atmospheric composition for climate, air quality and ozone layer applications. Remote Sensing of Environment, 120(SI), 70-83. DOI: 10.1016/j.rse.2011.09.027, 2012.

Further Links:

  1. Copernicus
  2. OMI
  3. Envisat
  4. Sentinel Missions Page
  5. Sentinel-5P Fact Sheet
  6. Julien Chimot’s Blog