Peter Schlüssel

Hyperspectral Earth Observation from IASI: Five Years of Accomplishments

The Infrared Atmospheric Sounding Interferometer (IASI) forms the main infrared sounding component of the European Organisation for the Exploitation of Meteorological Satellitess (EUMETSATs) Meteorological Operation (MetOp)-A satellite (Klaes et al. 2007), which was launched in October 2006. This article presents the results of the first 4 yr of the operational IASI mission. The performance of the instrument is shown to be exceptional in terms of calibration and stability. The quality of the data has allowed the rapid use of the observations in operational numerical weather prediction (NWP) and the development of new products for atmospheric chemistry and climate studies, some of which were unexpected before launch. The assimilation of IASI observations in NWP models provides a significant forecast impact; in most cases the impact has been shown to be at least as large as for any previous instrument. In atmospheric chemistry, global distributions of gases, such as ozone and carbon monoxide, can be produ...

Infrared Continental Surface Emissivity Spectra and Skin Temperature Retrieved from IASI Observations over the Tropics

AbstractLand surface temperature and emissivity spectra are essential variables for improving models of the earth surface–atmosphere interaction or retrievals of atmospheric variables such as thermodynamic profiles, chemical composition, cloud and aerosol characteristics, and so on. In most cases, emissivity spectral variations are not correctly taken into account in climate models, leading to potentially significant errors in the estimation of surface energy fluxes and temperature. Satellite infrared observations offer the dual opportunity of accurately estimating these properties of land surfaces as well as allowing a global coverage in space and time. Here, high-spectral-resolution observations from the Infrared Atmospheric Sounder Interferometer (IASI) over the tropics (30°N–30°S), covering the period July 2007–March 2011, are interpreted in terms of 1° × 1° monthly mean surface skin temperature and emissivity spectra from 3.7 to 14 μm at a resolution of 0.05 μm. The standard deviation estimated for t...

Retrieval of atmospheric temperature and water vapour from IASI measurements in partly cloudy situations

Abstract The Infrared Atmospheric Sounding Interferometer (IASI), that will be flown on Metop, is a nadir sounding instrument for the measurement of high-resolution atmospheric temperature and water-vapour profiles as well as other trace gases. Due to the opacity of clouds in the infrared domain the profile retrievals are likely perturbed by undetected clouds, partly filling the field of view of the instrument. The huge amount of spectral information contained in the IASI measurements is used to account for the effect of undetected clouds in the profile retrieval. Numerical simulations show that the water-vapour and temperature retrievals are not degraded if the cloud amount in single pixels is less than 5% and the occurrence of clouds is accounted for in the retrieval scheme.

Applications of IASI on MetOp-A: first results and illustration of potential use for meteorology, climate monitoring, and atmospheric chemistry

IASI was successfully launched on MetOP A on 19 October 2006. After the in-orbit commissioning, the performances of IASI were evaluated during the Cal/Val of level 1. Key parameters of instrument and on ground processing have been fixed for optimal performance and best quality data delivery. The first spectra and images of level 1 products show all the potential of IASI data for expected applications. Some illustrations are given here with maps of pseudo channels sensitive to trace gases, atmospheric profiles or maps of surface temperature qualitatively compared to maps from models. Level 2 processing to get these parameters has been implemented at Eumetsat and some products are currently under validation. The quality of IASI data paves the way to additional very promising products. A thorough analysis of cloud free spectra has been performed to extract the small signature of minor species like CFCs and HNO3. Nevertheless, the main limitation of IASI data remains clouds. It is showed here with the cluster analysis of AVHRR data registered in the IASI pixels and delivered as level 1 products that only a few cloud free pixels can used for full retrieval. A method making use of the cluster information has been developed. It permits to strongly increase the statistics where clear column profiles or columns above clouds can be retrieved. This scheme will be applied to the retrieval of the CO2 where large data set are needed to extract information from the spectra.

The 3MI mission: multi-viewing-channel-polarisation imager of the EUMETSAT polar system: second generation (EPS-SG) dedicated to aerosol and cloud monitoring

The Multi-Viewing-Channel-Polarisation Imager (3MI), planned to fly on the EPS-SG platform in the time-frame 2020–2040, is a 2D wide field of view radiometer dedicated to aerosol and cloud characterisation for climate monitoring, atmospheric composition, air quality and numerical weather prediction. The role of clouds in determining climate sensitivity to change is highly uncertain, in particular due to their multiple and complex interactions with aerosols. Hence new cloud observation systems (ground-based and space-borne) are needed for cloud monitoring. The purpose of the 3MI is to provide multi-spectral (from 410 to 2130 nm), multi-polarisation (-60°, 0°, and +60°), and multi-angular (10 to 14 views) images of the Earth top of atmosphere (TOA) outgoing radiances. First results from the 3MI synthetic data simulator will be presented. Although aerosol and cloud characterisation is the primary application, 3MI will further support observation of landsurface characteristics which will benefit from the enhanced directional and polarisation measurements and provide a better understanding of the Earth radiation budget. 3MI will also benefit from the synergy of other instruments flying onboard EPS-SG. Measurements from thermal infrared channels will be available from the METimage and IASI-NG instruments. Furthermore, the Sentinel-5 will provide information from the ultra-violet to the shortwave infrared, at a coarser horizontal sampling. The synergy with these instruments will also support 3MI with beneficial cross-calibration as 3MI will not have an onboard calibration and its radiometric performance will rely on vicarious calibration.

3MI: The Multi-Viewing Multi-Channel Multi-Polarization Imaging Mission of the EUMETSAT Polar System - Second Generation (EPS-SG) dedicated to aerosol characterization

The EPS-SG Multi-Viewing Multi-Channel Multi-Polarization Imaging Mission (3MI) is a radiometer dedicated to aerosol characterization for climate monitoring, air quality forecasts and Numerical Weather Prediction (NWP). The purpose of the 3MI concept, likewise that of the heritage missions POLarization and Directionality of the Earths Reflectances (POLDER) and Polarization & Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL), is to reconstruct a multi-spectral (from 410 to 2130 nm), multi-polarization (−60°, 0°, and +60°), and multi-angular (14 views) image of the Earth outgoing radiance at the top of the atmosphere (TOA) in order to resolve the directional anisotropy and the microphysical properties of aerosol.

Air-sea gas exchange: cool skin and gas transfer velocity in the North Atlantic Ocean during GasEx-98

Abstract Measurements of the Gas-Exchange Experiment GasEx-98 that took place in the North Atlantic Ocean from May to July 1998 are used with surface renewal theory to parameterise the temperature difference across the thermal molecular boundary layer of the ocean as well as the gas transfer velocity of CO 2 . The same parameterisations are used with satellite measurements to calculate basin-wide fields of boundary-layer parameters to obtain a broader overview of the air-sea exchange.

Overview of calibration and validation activities for the EUMETSAT polar system: second generation (EPS-SG) visible/infrared imager (METimage)

The EPS-SG Visible/Infrared Imaging (VII) mission is dedicated to supporting the optical imagery user needs for Numerical Weather Prediction (NWP), Nowcasting (NWC) and climate in the timeframe beyond 2020. The VII mission is fulfilled by the METimage instrument, developed by the German Space Agency (DLR) and funded by the German government and EUMETSAT. Following on from an important list of predecessors such as the Advanced Very High Resolution Radiometer (AVHRR) and the Moderate resolution Imaging Spectro-radiometer (MODIS), METimage will fly in the mid-morning orbit of the Joint Polar System, whilst the early-afternoon orbits are served by the JPSS (U.S. Joint Polar Satellite System) Visible Infrared Imager Radiometer Suite (VIIRS). METimage itself is a cross-purpose medium resolution, multi-spectral optical imager, measuring the optical spectrum of radiation emitted and reflected by the Earth from a low-altitude sun synchronous orbit over a minimum swath width of 2700 km. The top of the atmosphere outgoing radiance will be sampled every 500 m (at nadir) with measurements made in 20 spectral channels ranging from 443 nm in the visible up to 13.345 μm in the thermal infrared. The three major objectives of the EPS-SG METimage calibration and validation activities are: • Verification of the instrument performances through continuous in-flight calibration and characterisation, including monitoring of long term stability. • Provision of validated level 1 and level 2 METimage products. • Revision of product processing facilities, i.e. algorithms and auxiliary data sets, to assure that products conform with user requirements, and then, if possible, exceed user expectations. This paper will describe the overall Calibration and Validation (Cal/Val) logic and the methods adopted to ensure that the METimage data products meet performance specifications for the lifetime of the mission. Such methods include inter-comparisons with other missions through simultaneous nadir overpasses and comparisons with ground based observations, analysis of algorithm internal diagnostics to confirm retrieval performance for geophysical products and vicarious calibration to assist with validation of the instrument on-board calibration. Any identified deficiencies in the products will lead to either an update any auxiliary data sets (e.g. calibration key data) that are used to configure the product processors or to a revision of algorithms themselves. The Cal/Val activities are mostly foreseen during commissioning but will inevitably extend to routine operations in order to take on board seasonal variations and ensure long term stability of the calibrated radiances and geophysical products. Pre-requisite to validation of products at scientific level is that the satellite and instrument itself have been verified against their respective specifications both pre-launch and during the satellite in-orbit verification phase.

Calibration and validation of Level 1B radiances of the EUMETSAT polar system - second generation (EPS-SG) visible/infrared imager METimage

The EUMETSAT Polar System - Second Generation (EPS-SG) Visible/Infrared Imaging mission supports the optical imagery user needs for Numerical Weather Prediction (NWP), Nowcasting (NWC) and climate in the timeframe beyond 2020. The VII mission is fulfilled by the METimage instrument, to be flown onboard the Metop-SG-A satellite series. The instrument itself is a cross-purpose medium resolution, multi-spectral optical imager, measuring radiation emitted and reflected by the Earth from a low-altitude sun synchronous orbit with a swath width of 2700 km. Measurements will be made in 20 spectral channels ranging from 443 nm in the visible up to 13.345 μm in the thermal infrared at a spatial sampling distance of 500 m at nadir. This paper focuses on the Calibration and Validation (Cal/Val) activities planned for the METimage level 1B products to ensure that the calibrated and geolocated radiances meet the performance specifications for the lifetime of the mission. Such methods include cross-calibration with instruments on the same platform e.g. IASI-NG and Sentinel-5 measurements, inter-comparisons with other missions during simultaneous nadir overpasses, comparisons with ground based observations and lunar calibration. The level 1B product performance will be validated with respect to geometric, spectral, and radiometric requirements for all geographic regions including their seasonal variability. In particular the following specific activities are described: • Calibration verification • Validation of radiometry • Geometric verification • Image quality verification As the commissioning phase is limited in time, the products from METimage have to be confidence checked and validated with a concise focus on essential tests. The Cal/Val activities will extend to routine operations in order to ensure long term stability of the calibrated radiances and continually improve the calibration throughout the lifetime of the mission.

Vicarious calibration of the multiviewing channel polarisation imager (3MI) of the EUMETSAT Polar System-Second Generation (EPS-SG)

The Multi-Viewing -Channel -Polarization Imager (3MI), planned to fly on the Metop-SG satellite as part of the EPS-SG programme in the timeframe beyond 2020, is a radiometer dedicated to aerosol and cloud characterization for climate monitoring, atmospheric composition, air quality and numerical weather prediction. The purpose of the 3MI is to provide multi-spectral (12 channels between 410 and 2130 nm), multi-polarization (-60°, 0°, and +60°), and multi-angular (10 to 14 views) images of the Earth top of atmosphere outgoing radiance. 3MI does not have an onboard calibration facility and its radiometric and geometric performance will rely on vicarious calibration. The aim of this paper is to present the state of the art of vicarious calibration methods applicable to 3MI. The 3MI measurement principle is based on the French atmospheric mission PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) heritage [1]. This allows adapting the vicarious calibration methods of the PARASOL mission to the needs of 3MI. However, the monitoring of the SWIR (short wave infrared) channels will be a new challenge for the 3MI calibration as this spectral range was not present on PARASOL. The cross-calibration with other instruments flying on the same satellite will support the calibration of 3MI. Indeed the Metop-SG payload includes two other optical instruments covering the same spectral regions. METimage and Sentinel-5 will both be equipped with on-board calibration capabilities and provide valuable measurements for vicarious calibration of 3MI. Further cross-calibration with Earth observation instruments on other satellites, will be studied.