The Meteosat Third Generation (MTG) Programme is a EUMETSAT geostationary satellite mission developed by the European Space Agency (ESA). It will ensure the future continuity with, and enhancement of, operational meteorological (and climate) data from Geostationary Orbit as currently provided by the Meteosat Second Generation (MSG) system. The MTG satellites series is composed of 4 MTG-I and 2 MTG-S to bring to the meteorological community a continuous Imagery and Sounding capabilities with high spatial, spectral, and temporal resolution observations including geophysical parameters of the Earth based on state-of-the-art sensors. The first satellite (MTG-I1) was launched on 13th December 2022 by an Ariane 5 rocket. The commissioning of the whole system is expected to span over 2023. As part of the space segment of the mission, ESA and EUMETSAT performed the commissioning phase with the support of the Prime Contractor and the main unit's sub-contractors and suppliers. The recurrent satellites are being integrated and stored awaiting the availability of launchers, with a plan to launch MTG-S1 in Q1/2025 and MTG-I2 in Q1/2026. The main elements of the MTG-S1 satellite are now integrated and undergoing module level on-ground testing. This paper will address the overall mission and its instruments high level design features. It will introduce the MTG-I1 satellite performances as measured in-orbit and processed during the commissioning phase, before entering the routine operations and will discuss the future.
C. Montcalm, A. Badeen, D. Burbidge, R. Bruce, G. Carlow, J. Dane, N. Firdawsi, G. E. Laframboise, A. Miles, J.-P. Noel, R. Rinfret, B. Sullivan, R. Bardazzi, S. Lorenzini, L. Giunti
This paper presents the design, manufacture and characterization results of two optical interference filters to be used in the Lightning Imager (LI) optical head on the Meteosat Third Generation (MTG) mission. The first optical filter is a Solar Rejection Window (SRW) to limit the solar thermal radiation absorbed by the optical head while the second optical filter is a Narrow Band Filter (NBF) intended to only pass the lightning discharge emission wavelengths. Each filter has its own distinctive design considerations and manufacturing challenges. The SRW must pass wavelengths from the 760 to 780 nm spectral range and reject (block) wavelengths from the ultraviolet (UV) to the mid-wave infrared (MWIR) and up to 16.3° angle of incidence (AOI) and over a large temperature range (as when exposed to direct sunlight). The NBF is designed to pass only the oxygen emission triplet, centered around the 777.6 nm (vacuum) wavelength and rejecting other wavelengths. Considering the AOI of the light and the temperature excursion, the center wavelength (CWL) uniformity has to be better than 0.04% peak-to-valley (PV) over the 114 mm diameter clear aperture, which is a formidable challenge. We achieved a coating thickness uniformity less than ±0.01% PV, exceeding the prescribed specification. Post-deposition annealing was carried out to tune the bandpass to within pico-meters (pm) of the target CWL value while maintaining the desired CWL uniformity. To ensure that both the SRW and NBF filter meet the desired optical and physical specifications, a comprehensive series of optical and physical characterization tests, along with durability tests, were carried out on each deposition batch.
The Lightning Imager for Meteosat Third Generation is an optical payload with on-board data processing for the detection of lightning.
The instrument will provide a global monitoring of lightning events over the full Earth disk from geostationary orbit and will operate in day and night conditions.
The requirements of the large field of view together with the high detection efficiency with small and weak optical pulses superimposed to a much brighter and highly spatial and temporal variable background (full operation during day and night conditions, seasonal variations and different albedos between clouds oceans and lands) are driving the design of the optical instrument.
The main challenge is to distinguish a true lightning from false events generated by random noise (e.g. background shot noise) or sun glints diffusion or signal variations originated by microvibrations. This can be achieved thanks to a ‘multi-dimensional’ filtering, simultaneously working on the spectral, spatial and temporal domains.
The spectral filtering is achieved with a very narrowband filter centred on the bright lightning O2 triplet line (777.4 nm ± 0.17 nm). The spatial filtering is achieved with a ground sampling distance significantly smaller (between 4 and 5 km at sub satellite pointing) than the dimensions of a typical lightning pulse. The temporal filtering is achieved by sampling continuously the Earth disk within a period close to 1 ms.
This paper presents the status of the optical design addressing the trade-off between different configurations and detailing the design and the analyses of the current baseline. Emphasis is given to the discussion of the design drivers and the solutions implemented in particular concerning the spectral filtering and the optimisation of the signal to noise ratio.
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