The Multi-View, Multi-Channel, Multi-Polarisation Imaging (3MI) instrument is a passive scanning radiometer dedicated to aerosol characterisation, air quality and numerical weather prediction, as well as climate monitoring and more generally characterisation of the microphysical properties of the atmosphere, including clouds. The 3MI mission has heritage from the POLarization and Directionality of the Earth's Reflectances (POLDER) on-board the ADEOS and PARASOL satellites. Compared to POLDER, 3MI has improved spatial coverage, higher spatial resolution, and an expanded spectral range with more spectral bands in the reflective part of the spectrum, all bands being polarised (except absorption bands). It is scheduled for launch on the EPS-SG platform in 2024.
3MI’s mission is to provide images of the Earth Top-Of-Atmosphere outgoing radiance for 12 different spectral bands (from 410nm to 2130nm), with 3 different polarisers (-60°, 0° and +60°), and 14 angles. The design consists of two optical heads (SWIR and VNIR) composed by a detector along with a filter and polariser rotating wheel and a wide field-of-view optics. The multi-view is achieved by several successive overlapping acquisitions of the same Earth-Atmosphere target under different angles thanks to the instrument large field of view.
Using the experience acquired for the POLDER missions, CNES is cooperating with EUMETSAT and is providing the necessary analysis and expertise for the in-flight calibration and/or validation of several key parameters, both for geometric and radiometric aspects. Here we present the different methodologies that will be used to achieve that goal.
KEYWORDS: Sensors, Reflectivity, Device simulation, Short wave infrared radiation, Polarization, Instrument modeling, Picture Archiving and Communication System, Satellites, Ray tracing, Signal to noise ratio
The 3MI instrument is a multi-directional spectro-polarimeter to fly on-board the Metop-SG platform to be launched in 2022, as part of EUMETSAT’s EPS-SG system space segment. As for most of radiometers devoted to Earth Observing from space, the radiometric budget is a system budget which includes many contributors, from the raw detector signal-to-noise to the artefact introduced by the ground correction in level-1 processing. The straylight happening in the optics is one of these contributors which could sometimes become dominant in the system budget. In this context, it is required to constrain the instrumental design as well as the ground characterization and its correction by processing. This is supported by maintaining accurate understanding of the straylight and its behaviour from early on in the project in order to check its radiometric level and quantify the potential impact on the products. This paper will present the analysis done to understand and model the physical behaviour of 3MI’s straylight. Based on initial inputs from the instrument builders and assuming some simplification, a physical straylight model was derived. This model allows an easy implementation in a simulator able to add this straylight contribution to any type of images, particularly on very realistic scenes. Our physical model shows advantageous complementarity to the builder’s simulations in the sense it allows a better quantification on a wide variety of realistic images while specifications usually assume theoretical targets such as a knife-edge transition. Such a capability is needed for 3MI system activities, in particular to cope with any deviation to the performance requirements. This paper presents examples of 3MI straylight-impacted images simulated at EUMETSAT using as input 1/ a simulation of the straylight provided by the instrument builder (ESA and Leonardo), and 2/ a realistic test data set based on PARASOL and MODIS acquisitions from the A-train observatory generated by ICARE/LOA. This simulator will be used during the development of the 3MI instrument and its ground characterization in order to monitor the impact on products.
The Multi-Viewing -Channel -Polarisation Imager (3MI), planned to fly on the Metop-SGA satellites as part of the EUMETSAT Polar System - Second Generation (EPS-SG) programme in the timeframe beyond 2020, is a radiometer dedicated to aerosol and cloud characterisation 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 nm and 2130 nm), multi-polarisation (-60°, 0°, and +60°), and multi-angular (10 to 14 views) images of the Earth top of atmosphere outgoing radiance.
The 3MI concept is based on the PARASOL mission heritage. This heritage allows adapting techniques developed for PARASOL e.g. for the vicarious calibration methods. As PARASOL, 3MI does not have an onboard calibration facility and its radiometric and geometric performances will rely on vicarious calibration. However the monitoring of the SWIR (short wave infrared) channels will be the new challenge for the 3MI calibration as this spectral range was not present on PARASOL. Because the vicarious methods may have less accurate performance for absorption bands (763 nm, 910 nm, and more specifically the SWIR 1370 nm), the access to a moon observation during commissioning would be very beneficial, in addition to the characterization of many other radiometric aspects. The Metop-SGA satellite will also allow simultaneous temporal and geometrical acquisitions between the payload instruments. This synergy will be beneficial to support 3MI with cross-calibration (radiometric, spectral, and geometric). Indeed the Visible-Infrared Imager (METimage) and the UV-VIS-NIR-SWIR Sounder (Sentinel-5), the two other optical instruments covering the similar spectral regions will be both equipped with on-board calibration and provide valuable measurements for cross-calibration with 3MI.
The 3MI instrument is one of the missions of the EPS-SG program to be launched in 2021. This polarimetric mission is a heritage of the POLDER mission, with improved capabilities and now placed in a fully operational long- term framework. The spectral range was extended from the visible-near-infrared (410 to 910nm) to the shortwave- infrared domain (up to 2200nm). The spatial resolution (4km at nadir) and the swath (2200×2200km2) were also improved compared to previous POLDER instruments. The 3MI concept of the multi-viewing, multi-spectral and multi- polarized Imaging will be described, especially how these 3 information are acquired together with one instrumental concept that remains simple. The performance necessary to meet the mission requirements will be initially reached before launch through a fully dedicated ground campaign and maintained once in orbit through an extensive vicarious calibration strategy. The level 1 products available to the users will be geolocated Stokes vectors on the native geometry (Level 1B) and geoprojected multi-directional and spectral Stokes vectors (Level 1C). Level-2 products will provide geophysical and microphysical parameters for aerosol and clouds. The presentation will detail the 3MI concept, overview the mission characteristics, and browse the foreseen ground campaign and in-flight strategy necessary to reach the performance, as well as the products available to the users.
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.
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.
The Multi-viewing ,Multi-channel, Multi-polarisation Imager (3MI) of the EUMETSAT Polar System - Second Generation (EPS-SG) is a two-dimensional push broom radiometer dedicated to aerosol characterisation for climate monitoring, air quality forecasting and Numerical Weather Prediction (NWP). The purpose of the 3MI concept is to provide a multi-spectral (from 410 to 2130 nm), multi-polarisation (-60°, 0°, and +60°), and multi-angular (10 to 14 views) image of the Earth outgoing radiance at the top of the atmosphere (TOA) in order to accurately measure the aerosol load and thereby resolve the directional anisotropy and the microphysical properties of aerosol. The 3MI heritage comes from the Polarisation and Directionality of the Earth's Reflectances (POLDER) and Polarisation and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL), with 3 instruments launched since 1996.
Satellite observations provide unique opportunities for the identification of trace gas sources on a global scale. We present case studies for the synergistic use of satellite observations by comparing formaldehyde (HCHO) time series with fire count measurements as well as with surface temperature to identify the tropospheric sources of HCHO. The fire counts and temperature are taken as proxy for biomass burning events and vegetation activity, respectively. Both are sources of HCHO, either direct or trough photochemical oxidation of non-methane hydrocarbons (e.g. biogenic isoprene emissions). Formaldehyde time series are derived from satellite observations made by the GOME instrument. This instrument provides almost 8 years of continuous HCHO global observations, which constitute an ideal case to calculate time series over specific regions for various trace gases.
Nine regions have been selected to investigate the influence of fire counts (biomass burning proxy) and the temperature (vegetation activity proxy) on the HCHO tropospheric columns. The chosen time series has a length of 6 years (from
July 1996 to June 2002). The results show that biogenic sources of HCHO are in many cases the strongest HCHO sources. For example over south east of the USA, the correlation with temperature was very high indicating a strong biogenic source of HCHO (through isoprene emissions). The biomass burning source typically shows more pronounced
seasonal patterns or is even of sporadic nature. Over the Amazon region, the correlation with fires is high indicating that in this area most of the HCHO is caused by biomass burning. In several other regions for both sources moderate correlation coefficients were found.
SCIAMACHY (Scanning Imaging Absorption spectroMeter for Atmospheric ChartographY) is the first instrument to
allow retrieval of CO by measuring absorption in the near infrared from reflected and scattered sunlight instead of from
thermal emission. Thus, in contrast to thermal-infrared satellites (MOPITT), SCIAMACHY is highly sensitive to the
lower layers of the troposphere where the sources, such as biomass burning, are located, and where the bulk of the CO is
usually found.
In many regions of the world, the burning of vegetation has a repeating seasonal pattern, but the amount of CO emitted
from biomass burning varies considerably from place to place. Here we present a study on the relationship between fire
counts and CO vertical column densities (VCD) in different regions. These results are compared with the CO VCD from
MOPITT, aerosol index, and NO2 tropospheric VCD (TVCD) from SCIAMACHY, and the coupled chemistry climate
model (CCM) ECHAM5/MESSY.
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