During the last decade, meteorology domain has lived many breakthroughs. In the field of remote sensing from space, one of the most significant advancement is in the use of Thermal Infrared sounders. Thales Alenia Space delivered sounders flagship METOP/IASI, resulting in the enhancement of meteorological events forecast and unprecedented 3D atmospheric knowledge. The next generation of European geostationary meteorological satellites, Meteosat Third Generation is currently being realized through the well-established and successful Cooperation between EUMETSAT and ESA with Thales Alenia Space being overall MTG prime contractor. MTG encompasses two kinds of satellites: an imaging mission MTG-I with the FCI imaging payload derived from the MSG-SEVIRI with a payload complement of a lightning detection system (LI as the Lightning Imager) and a sounding mission MTG-S with the payload complement including the thermal infrared sounding payload IRS (full disc coverage) and the Copernicus payload UVN/S4, a spectrometer in UV/VIS/NIR bands to retrieve air quality in Europe. Stemming from IASI, Thales Alenia Space is now developing the IRS interferometer as well as the detection and onboard processing chain. These key elements will be integrated by OHB which is the IRS instrument as well as MTG-S satellite Prime Contractor. Reaching performance from a geostationary orbit is a two-order of magnitude more stringent challenge compared to a LEO instrument. Thales Alenia Space did elaborate new and innovative technology to ensure sub nanometric interferometer metrology and thus to achieve real time on-board corrections. Two essential validation milestones have been achieved in 2019. • The interferometer engineering model was thoroughly tested successfully, especially in terms of spectral performance vs. microvibrations. • Thales Alenia Space has also tested the IRS “core spectrometer” engineering model, allowing to test the full spectrometer chain of the instrument by synchronizing the interferometer itself with the two 160x160 pixel detector arrays of the detection chain and the on-board data processing unit that is able to process the 2Gbit/s raw data flow generated by the instrument. The paper will focus on the two major outcomes of this test campaign: • The demonstration of the functionality of IRS new 3D metrology system, its associated processing and its benefits. • An overview of performances achieved during those two intensive test campaigns. In particular Spectral Response Function (SRF) knowledge/prediction, which is essential to support an unprecedented interpretation of the spectra and final products retrieval accuracy.
Meteosat Third Generation (MTG) is the next challenging mission for accurate observation of the Earth dedicated to meteorology forecast. MTG encompasses two different missions: MTG-I (Imaging) and MTG-S (Sounding). MTG-I optical payload counts the FCI (Flexible Combined Imager), a multi-spectral imager in the continuity of Meteosat Second Generation (MSG) with improved performance and additional spectral bands. MTG-S transports the IRS instrument which is an Infrared Fourier Transform Spectrometer dedicated to the sounding of the atmosphere inspired by the previous IASI mission. Located in a geostationary orbit, the satellites are covering the full hemisphere for imaging (FCI) in less than 10 minutes in 16 different spectral bands from Visible to Very Long Wave IR at a resolution of 0.5-2 km and make a complete IR sounding of the atmosphere (IRS) in less than 1h at a spatial resolution of 4 km and a spectral resolution of 0.625 cm-1. In this article, we describe the detection chains of FCI and IRS instruments which give accurate sight to the remote sensing and afford the capability to reach the objectives of MTG-I and S missions. Some particularities of designs and key performance are presented. MTG on ground tests have provided interesting results which are therefore presented. These results have been obtained after 10 years of intensive research and development at Thales Alenia Space (Prime FCI) and OHB(Prime IRS), with the support and supervision of ESA and EUMETSAT. This research and development work has been performed under an ESA contract.
Detectors used in imaging systems always generate optical reflections as the light is never completely absorbed. To estimate or measure the detector optical reflections permits to better manage the induced parasitic photonic signals (ghost and scattering) in imaging devices. We describe different methods to assess these detector reflections. Among them, a powerful test based on etalon effect in Focal Plan Array is detailed for measuring the reflection at different wavelengths even near the cut-off of the detector sensitivity. The physical effects in PV junctions that can explain the observed optical reflections are discussed.
Noise Equivalent Temperature Difference is a key point for the evaluation of IR detectors and imaging systems. Our theoretical model of temporal noise predicts the NETD and responsivity of detectors with an accuracy better than 3 mK and 5 %, respectively in a large range of scene temperatures and integration times. This study clearly shows that we are able to estimate the temporal noise in any configuration and particularly for scene temperatures not easily accessible in standard laboratory conditions. Also, we can measure the amplitude of different noise contributions (1/f, white noise) and the FPA leakage current.
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