Team: GHG & Calibration

1. development of calibration methods for Earth observation systems of the atmosphere
2. development of algorithms for the calculation of greenhouse gas parameters in the atmosphere

Both, active and passive systems can be used for remote sensing of the Earth's atmosphere.

Active sensing instruments have an onboard signal source, i.e. they emit light or other signals and analyse the reflection from the ground or from the atmosphere. Compared to passive instruments that use reflected sunlight as a signal source this has the advantage that

• the emitted signal and the signal path are well known, and
• measurements can be carried out regardless of the position of the sun (especially at night).

In atmospheric exploration, so-called LIDAR systems (Light Detection and Ranging), which use lasers as a light source, are used. Short laser pulses are emitted from the satellite and the backscattering of the light is analysed. While ground-based and airborne LIDAR systems have been around for some time, satellite-based LIDAR measurements are a relatively new development. IMF is involved in two LIDAR missions: Aeolus to measure global wind fields and MERLIN (Methane Remote Sensing LIDAR Mission) to measure the greenhouse gas methane (CH4). IMF is working closely with the DLR Institute of Atmospheric Physics (IPA) on these missions.

Passive systems use the sunlight reflected from the earth to record spectra. The advantage of passive systems is that they can measure large areas simultaneously and thus achieve global coverage in a short time. Starting with GOME-1 (1995) up to the current Copernicus atmospheric missions Sentinel-5P/Sentinel-4/Sentinel-5, our department has been involved in the development of algorithms for instrument calibration and the determination of atmospheric trace gases for 30 years. We have developed the processing system GCAPS (Generic Calibration and Processing System) for use in operational ground segments of earth observation systems. GCAPS is generic, i.e. the framework can be used for a wide variety of instruments and applications. Algorithms and the reading and writing of data products are implemented as plug-ins.

For the calculation of greenhouse gas concentrations, we use the internally developed  Py4CAtS  software package (Python for Computational ATmospheric Spectroscopy). Py4CAtS is a radiative transfer model that is used in the infrared and microwave spectral range. Thanks to its modular structure, it can be used flexibly in various scenarios, in particular as a forward model for inversion methods that are being developed in the research group. Py4CAtS and corresponding inversion algorithms are used to precisely determine trace gas and greenhouse concentrations from satellite and aircraft measurements. Py4CAtS is also used in research into the spectra of exoplanets. A more recent development is the calculation of methane from measurements made by DLR's HySpex airborne instrument. Here we were able to show that our algorithms can determine methane emissions even from data with relatively low spectral resolution.

We are continuously developing both GCAPS and Py4CAtS.

The GHG & Calibration group is currently involved in the following projects:

FDR4ATMOS

This ESA project is developing algorithms to harmonise radiances from the GOME/ERS-2, SCIAMACHY/ENVISAT and GOME-2 missions on MetOp-A/B/C. Our group is leading a consortium with IUP Bremen, BIRA-IASB, NPL UK and ESS. More information can be found on FDR4ATMOS homepage.

MERLIN Mission

The MERLIN mission will measure methane with high precision. After carbon dioxide (CO2), methane is the second largest contributor to anthropogenic, i.e. man-made, global warming. It is mainly produced by biogenic processes, e.g. decomposition processes, rice cultivation or livestock farming. Knowledge of the sources and sinks of methane is important in order to be able to reliably predict climate change. MERLIN's ability to measure permafrost areas during the polar night is particularly important, as passive instruments can only collect useful data on these areas during the local summer. As an active instrument, MERLIN is not subject to this restriction and can measure day and night all year round.  MERLIN is a Franco-German project, with France responsible for the platform and Germany for the payload. The launch of MERLIN is scheduled for 2029. In MERLIN, the IMF is responsible for the implementation of the operational Level 1 processor and, together with IPA, is involved in the development of the calibration algorithms and a Level 2 processor. The department also carries out the long-term monitoring of the instrument. Various instrument parameters are monitored in order to be able to react to changes in the instrument at an early stage. In addition to DLR institutes, CNES (the French space agency) and other French institutes, the MERLIN consortium also includes Airbus Defence and Space, responsible for the construction of the instrument, and the company SciSys, responsible for the transmission of instrument data and the data user interface.

Aeolus and Aeolus-2 mission

The Aeolus mission is the first space-based Doppler wind LIDAR for the global measurement of wind profiles in the troposphere and the lower stratosphere. The LIDAR measurement of wind speeds utilises the fact that light which is backscattered by the moving atmosphere undergoes a wavelength shift due to the so-called Doppler effect. The speed of the backscattering particle and thus the wind speed in the direction of the beam can be calculated from the extent and direction of the shift. Following the successful first Aeolus mission, which measured wind profiles from 2018-2023, a follow-up mission is planned for the early 2030s. In the new mission, IMF is also involved in the so-called Level 1 processing (i.e. for the calibration of the detector signals) and is responsible for the development of the Level 1 processors. In addition, the IMF also carries out development tasks for the operational Level 2A processor. IMF is also involved in data analysis and algorithm development for the first Aeolus mission, which is still ongoing.

CO2Image