Analysis of MTG‐IRS observations and general channel selection for numerical weather prediction models

Abstract

The Infrared Sounder (IRS) is an infrared Fourier transform spectrometer that will be on board the Meteosat Third Generation series of the future European Organization for the Exploitation of Meteorological Satellites geostationary satellites and will have a unique four‐dimensional look at the atmosphere. After its planned launch in 2024, it will be able to measure the radiance emitted by the Earth at the top of the atmosphere using 1,960 channels in two spectral bands between 680–1,210 cmprefix−1$$ {}^{-1} $$ (long‐wave infrared) and 1,600–2,250 cmprefix−1$$ {}^{-1} $$ (mid‐wave infrared) at a spectral sampling of 0.6 cmprefix−1$$ {}^{-1} $$. It will perform measurements over the full Earth disk with high spatial and temporal resolution of 4 km at nadir and 30 min over Europe. Thus, the huge amount of data from IRS will present challenges, particularly in data transmission, data storage, and assimilation into numerical weather prediction (NWP) models. To reduce the volume of data, various methods are available, including spatial sampling, principal component analysis, and channel selection. The latter technique will be discussed in this paper by proposing general channel selection to provide NWP models. The objective of this selection is to improve essential variables for NWP such as temperature, humidity, skin temperature, and ozone. This work has required the development of a large observation database and takes into account the main developments in assimilation techniques, including the use of full observation‐error covariance matrices or the assimilation of ozone in global models, for example. This study performs a specific analysis of the sensitivity of IRS observations and proposes a first general selection of 300 channels for NWP models. This selection allows us to reduce the analysis error in the troposphere by 48% in temperature, 65% in humidity, and 17% in ozone.

Preparing the assimilation of the future MTG‐IRS sounder into the mesoscale numerical weather prediction AROME model

“…For the experiments assimilating the IRS reconstructed BT, we chose to use a subselection of 75 channels from the 300‐channel selection made in (Coopmann et al ., 2022). The 75‐channel set includes 27 temperature‐sensitive channels, 27 water‐vapour‐sensitive channels, and 21 atmospheric window channels.…”

“…These results have allowed us to validate the correct functioning of the cloud detection for our synthetic IRS observations, which will be a guarantee of reliability during the 3D‐Var AROME data assimilation experiments. A more detailed study is provided also in (Coopmann et al ., 2022).…”

Assessment of the contribution of IRS for the characterisation of ozone over Europe

“…Another point that arose from the study on the preparation of the NR framework has been the possibility to perform a channel selection, while maintaining a good quality in the assimilation results. This is also a commonly used procedure in NWP for many instruments, that has been explored at CNRM for IRS [Coopmann et al (2022)] and in the context of another future hyperspectral infrared instrument IASI-NG (IASI new generation) [Vittorioso et al (2021)]. Since the work carried out here on IRS was a first analysis, we wanted to investigate the behaviour of all the consecutive wavelengths considered.…”

“…The information about IRS reported in this subsection are issued from EUMETSAT, Thales Alenia Space and Coopmann et al (2022).…”

Enhancing Clear Radiance Generation for Geostationary Hyperspectral Infrared Sounder Using High Temporal Resolution Information

“…However, GeoHIS provides high temporal resolution observations, which are critical for tracking rapidly changing parameters such as atmospheric water vapor. The temporal resolution for GeoHIS can be as high as 5 min (Coopmann et al., 2023) over a designated region, this offers a unique opportunity to enhance clear radiance generation using temporal information. For example, within a relatively short period (e.g., less than 15 min), it is usually reasonable to assume that the atmospheric profile remains unchanged or changes minimally within that time window.…”