Top of the atmosphere view from ISS

Top-Of-Atmosphere simulations for Copernicus CO2M

Photo Credit: NASA/ISS

Top of the atmosphere view from ISS
Top of the atmosphere view from ISS

This study will provide EUMETSAT with Top-Of-Atmosphere simulations for the evaluation of data processing for the forthcoming Copernicus CO2M mission.

Last Updated

16 June 2021

Published on

15 June 2020

The study will produce a set of simulated measurements for the planned Copernicus CO2 monitoring mission (CO2M). The test data is intended to be used to test the operational processors which will be developed (via parallel activities) to analyse flight data.

Data from this study will be delivered in the planned (Level 1) format for top-of-atmosphere radiance data from the CO2M spectrometers. Accurate simulation of the CO2M spectrometer radiances is highly computationally intensive. It involves modelling polarised multiple scattering in the atmosphere and at the surface, including detailed representation of the many molecular absorption lines.

Much of the work of this study involves developing tools capable of simulating orbits of data within reasonable computational resources. The tools are to be developed in a flexible way such that it will become relatively straightforward to perform further work to simulate radiances for new test conditions and for the imaging sensors also planned for CO2M.

The main instrument on the proposed CO2 monitoring platform CO2M is the imaging grating spectrometer (Figure 1), measuring in the visible region between 405 and 490 nm, in the near infra-red between 747–773 nm and in two bands in the short-wave infra-red between 1590–1675 and 1990–2095 nm, with a spectral resolution between 0.12 and 0.6 nm. This study will simulate Top-of-Atmosphere radiances from these instruments for multiple day-side orbits and for a swath-width wider than 250 km.

 Instrument details and simulated outputs
Figure 1: Instrument details and simulated outputs


  • Implement a documented and configurable system for realistically simulating radiance measurements by the visible/near-ir/short-wave-ir spectrometers (NO2IS and CO2IS) on the CO2M.
  • Use the system to generate (at least) three orbits of realistic level 1 data. Orbit geometry, sensor spatial sampling and L1 format are being provided by EUMETSAT. Correctly formatted L1 files will be provided, containing all necessary information to enable the L2 processors to be realistically tested.


The work is divided into four tasks:

  1. Setup of the radiative transfer model and input data. This work builds on existing tools developed and applied in an earlier EUMETSAT study to generate test data for Copernicus Sentinel-4 and 5 [Test Data for the EPS-SG instrument UVNS, NOV-7427-NT-4988, issue 4.]. A fast but accurate approach to simulate molecular absorption with polarised multiple scattering from cloud, aerosol and surface is developed.
  2. Collection of input data, including information on orbit sampling (from EUMETSAT), and the atmospheric state from a combination of model data from the CO2 Human Emissions (CHE) project and CAMS reanalysis.
  3. Production of the CO2IS datasets. Work will be carried out using the UK Jasmin high performance computing facility. The quality of the resulting data will be extensively tested and results formatted as required.
  4. Project Outreach. Results will be presented in suitable academic conferences. A peer reviewed publication is also planned.

The methods used and products produced by the study will be documented in a suite of technical reports.