Requirements for CO2 monitoring by Sentinel-5

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Front page of the final report “Requirements for CO2 monitoring by Sentinel-5”

What is it?

“Requirements for CO2 monitoring by Sentinel-5” was an ESA contract study (ESA contract number 4000103801) finished in March 2012 and with the main objective of evaluating the capabilities of the Sentinel-5-UVNS sensor in a view of CO2 monitoring. The consortium was led by NOVELTIS and included University of Leicester (ULe), University of Bremen (IUP-UB), The Royal Netherlands Meteorological Institute (KNMI), and Laboratoire des Sciences du Climat et de l’Environnement (LSCE).

The context

The Sentinel-5 mission is part of the COPERNICUS initiative, the overall objective of which is to support Europe goals regarding sustainable development and global governance of the environment by providing timely and quality data, information, services and knowledge. Within the COPERNICUS Space Component Programme, Sentinel-5-UVNS covers the needs for continuous protocol monitoring of atmospheric composition, in particular with respect to air quality and climate, with a UV/Visible/Near-Infrared/SWIR (UVNS) sounder to be deployed on the next generation of the European operational polar meteorological satellite series MetOp Second Generation (MetOp-SG) in low Earth orbit (LEO). The target species including O3, NO2 – Nitrogen dioxide, SO2, HCHO and aerosols.

In the context of global climate change induced by a continuing increase in the average global temperature, the needs for CO2 – Carbon dioxode monitoring are part of the GMES operational system [RD41]. Indeed, the increase of the greenhouse gases (GHG) such as CO2 – Carbon dioxode, but also CH4 – Methane and N2O – Nitrous oxide are the major contributors on the modification of the global temperature. Despite the clear user need to monitor atmospheric CO2 [RD27] [RD41] [RD60], the current baseline of the Sentinel-4 and -5 Mission Requirement [RD14] did not explicitly addresses CO2 with similar priority as atmospheric pollutants and CH4 – Methane.

However, the SWIR-1 (ShortWave InfraRed) designated band (1590-1675 nm) of the Sentinel-5-UVNS spectrometer includes spectral measurements of CO2 absorption.

Main objectives

The main objective of this study was to assess quantitatively the capabilities of the Sentinel-5-mission to provide useful information for monitoring CO2, with respect to the user needs, and to provide recommendations for improving the mission (if any).

The following issues had to be addressed:

  • What are the user requirements for CO2 monitoring?
  • What are the capabilities of the current Sentinel-5 baseline mission for CO2 monitoring?
  • What should be the improvements (if any) of the current S-5-UVNS instrumental specifications.

Main achievements

Extracted from the abstract of the final report:

This study was structured in 3 specific activities:

1. specification (on a consensus basis) of quantitative user requirements on the space-based XCO2 products in order to monitor CO2 surface fluxes for 3 specific applications focused on specific scales (global to regional scales, mega-cities and strong local scale)

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Task 1 diagram of the “Requirements for CO2 monitoring by Sentinel-5” project

2. an assessment of the XCO2 products retrieved from current and improved instrument specifications, achieved through 3 independent algorithms with comparison to the key XCO2 requirements (i.e. spatial scales, random errors and systematic errors),

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Task 2 diagram of the “Requirements for CO2 monitoring by Sentinel-5” project

3. and an Observing System Simulation Experiment-like exercise which allows the link of the Sentinel-5 XCO2 performances to CO2 L4 error improvement.

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Task 3 diagram of the “Requirements for CO2 monitoring by Sentinel-5” project

By simulating a wide variety of geophysical conditions, the study has demonstrated the potential of Sentinel-5 (in its baseline configuration) for monitoring CO2 surface fluxes at global to regional scales. For the expected XCO2 products derived from Sentinel-5 (in its baseline configuration), with a random error (threshold) of 4 ppm and a systematic error (threshold) of 2 ppm, the associated objectives will be fulfilled at least in parts, particularly through the global coverage and good spatial resolution of the Sentinel-5 mission (pixel size equal or smaller than 10 km).

Actual retrievals have shown a good consistency between the results of the 3 independent algorithms. Performances are better than the thresholds quoted above (random and systematic) in 80% of the cases (after filtering out the “bad “retrievals). The highest XCO2 systematic error values, which are the most critical parameters when assessing the capabilities of a dedicated CO2 space-borne mission, are mainly related to major scattering effects (induced by uncertainties in aerosol and cirrus parameters) and are not well enough reduced by the retrieval algorithms.

CO2 applications related to smaller scales remain out of reach mainly because of the horizontal resolution. The importance of the spatio-temporal dependence of XCO2 systematic errors, with respect to the scale of the monitored CO2 surface fluxes has been underlined through the OSSE-like exercise. Options for enhancing XCO2 Sentinel-5 performances, by improving associated instrument specifications above the current baseline, have been examined.

The main priorities are: 1) to add a 2 micron spectral channel measuring the strong 2 micron CO2 absorption band, 2) to improve the spectral resolution in the NIR-2 spectral region (from 0.4 nm, as currently specified, to 0.12 nm).

Finally, 2 additional recommendations are addressed: 1) to establish a robust filtering methodology which could be based on ancillary information provided by VII and/or 3MI measurements, 2) to further develop the XCO2 retrieval algorithms for being able to fully exploit the information of 3 spectral bands (NIR-2, SWIR-1 and SWIR-2) simultaneously.

Group members

More information?

  • Final report and presentation here
  • Status Overview of the GMES Missions Sentinel-4, Sentinel-5 and Sentinel-5p, presentation at ATMOS 2012 by Paul Ingman et al., here (mention of the project on SL20) here
  • Requirements for the GMES Atmosphere Service and ESA’s implementation concept: Sentinels-4/-5 and -5p by Paul Ingman et al., (2012) here

  • The COPERNICUS program here
  • The ESA Sentinel-5 mission here
  • Webpage on CO2 – Carbon dioxide here