Meteosat Third Generation (MTG): Preliminary Design of the Imaging Radiometers and Sounding Instruments Donny Aminou, Jean-Loup Bézy, Paolo Bensi ESA, Earth Observation Future Programmes Department and Rolf Stuhlmann, Stephen Tjemkes, Antonio Rodriguez EUMETSAT, Programme Development Department I will now present the EarthCARE system concept. The presentation is summarising the outcome of the feasibility studies which took place in Europe and in Japan. An overview of the mission is provided on this view graph. Each element will be detailed in the presentation. 11th SPIE International Symposium on Remote Sensing, 13-16 September 2004, Maspalomas, Gran Canaria, Canary Islands, Spain

MTG Observational Missions Based on the assessment of observing techniques, five candidate observation missions identified for MTG Three distinct imagery missions dedicated to operational meteorology, with emphasis on nowcasting and very short term forecasting: The High Resolution Fast Imagery (HRFI) mission, enhancement of the MSG HRV mission; The Full Disk High Spectral resolution Imagery (FDHSI) mission, successor to the MSG SEVIRI mission; The Lightning Imagery (LI) mission; An Infrared Sounding (IRS) mission focussed on operational meteorology, with some potential relevance to atmospheric chemistry; An UV/Visible sounding (UVS) mission dedicated to atmospheric chemistry http://www.eumetsat.de

High Resolution Fast Imagery (HRFI) Mission Successor of MSG HRV specified to meet the requirements for ‘information on rapid development phenomena’ Coverage Repeat cycle Local Area Cov. 18ox6o 5 min ‘Rapid Scan’ 6ox6o 5/3 min 0.5 km 1 km The High Resolution Fast Imagery (HRFI) mission expands the MSG High Resolution Visible (HRV) mission in the spectral domain. The emphasis is on high temporal (5 minutes) and spatial (0.5-1.0 km) resolution requirements, for a limited number (5) of spectral channels. The coverage is limited to selectable fractions of the full Earth disk.   The main objective of the HRFI mission is to support Nowcasting and Very Short Term Forecasting (VSRF) of convection and its relationship to the “fast” component of the hydrological cycle. This will be achieved through observations of cloud patterns, their horizontal movement, the vertical development of clouds, and micro-physical properties at cloud top. A second objective of the HRFI mission is to complement the MTG Full Disk High-Spectral resolution Imagery (FDHSI) and the Infrared Sounding (IRS) missions, in providing more detailed, “targeted” observations over selected regions where active weather patterns are developing. The HRFI will cover an area of 6 in the South/North or East/West direction and 18 centred at Sub-Satellite Point (SSP) variably placed over the Earth with a repeat cycle of 5 minutes or less. In addition the instrument is designed to perform rapid scan over area of 6x6 placed on any part of the Earth disk at shorter repeat cycle for monitoring of small scale phenomena.

High Resolution Fast Imagery (HRFI) Mission Still Under review Spatial resolution at SSP: 0.5 km - 1.0 km

Full Disk High Spectral Resolution Imagery (FDHSI) Mission Successor to remaining SEVIRI mission specified to meet the requirements for ‘quantitative information’ Coverage Repeat cycle Full Disk Coverage 18ox18o 10 min Local Area Cov. 18ox6o 10/3 min 1 km 3 km The Full Disk High Spectral Imagery (FDHSI) mission is an evolution of the MSG SEVIRI full disk mission, featuring high radiometric performances in a larger number of spectral channels from the visible up to the thermal infrared and full Earth disk coverage. It is also more demanding on temporal (10 minutes) and spatial (1 km - 3 km) resolution than the MSG SEVIRI mission. The FDHSI mission is composed of a core set of 15-channel and two optional sets of channels located in the visible (FD-OPT 1) and infrared (FD-OPT 2) parts of the spectrum. The main objectives of the FDHSI mission are to support: ·          Nowcasting and very short term forecasting; ·          Numerical Weather Prediction at regional and global scales; ·          Climate monitoring.   In the nominal imaging mode, the FDHSI covers the full Earth disk with a 10 minutes repeat cycle. A reduced scan mode is also proposed with a coverage equivalent to 1/3 of the full disk (18º E/W x 6º N/S) referred to as Local Area Coverage (LAC) at a shorter repeat cycle. The LAC can be variably placed over the Earth.

Full Disk High Spectral Resolution Imagery (FDHSI) Mission MSG heritage New Channels Under review Options

FDHSI Mission Optional Channels for cloud top height determination by differential absorption in the oxygen A-Band for cloud top height determination by CO2-slicing in the 14µm CO2 band

Spectral Channels of Imagery Missions MSG HRV MTG Imagery Core Channels Cloud slicing sounding channels in the 14 µm band Cloud top pressure (O2-A) Channels MSG VIS-0.4 VIS-0.6 VIS-0.8 NIR-1.3 NIR-1.6 NIR-2.13 IR-3.8 IR-6.7 IR-7.3 IR-8.5 IR-9.7 IR-10.8 IR-12.0 IR-13.3 IR-13.9 O2-A MTG FDHSI BRC: 10 min DX: 1 … 3 km CO2-14µm 2 bands or 4 narrow channels 4 narrow channels MTG HRFI NIR-2.13 VIS-0.6 IR-11.4 IR-7.3 IR-3.8 BRC: 5 min DX: 0.5 … 1 km 2 4 6 8 10 12 14 16 MSG SEVIRI BRC: 15 min DX: 1 … 3.5 km wavelength [µm]

MTG HRFI & FDHSI: Summary and Critical Results MTG compared to MSG: signal level HRFI FDHSI MTG Specification VIS-0.6 MSG Performance HRV Equivalent Signal ratio Spectral resolution 0.2 mm ~0.5 mm 2.5 Footprint 0.7 km 1.4 km 4 Spatial Distance 0.5 km 1 km Coverage 6° x 18° 18° x 18° 1/3 Repeat Cycle 5 minutes 15 minutes 3 Radiometric resolution 10 at 4.36 W/(m² sr µm) 1.2 at 1.22 W/(m² sr µm) 5.6 (*) Overall 225 MTG Specification IR 13.4 MSG Performance Equivalent Signal ratio Spectral resolution 0.3 mm 2 mm 6.7 Footprint 4.2 km 4.8 km 1.3 Spatial distance 2.5 km 3 km 1.44 Coverage Full Disk 1 Repeat Cycle 15 minutes Radiometric resolution 0.2 K at 270 K 0.37 K at 270 K 1.85 Overall 25 (*) photon noise limited performance

Imagery Mission Imaging Concept 2-axes gimballed scan mirror induces image rotation (±9°) when pointing south or north from equator implementation of image de-rotator (could be considered) Entrance pupil: Ø300mm Cooling: 85 K passive cooling for HRFI 50 K passive cooling for FDHSI Calibration device: full pupil IR source at telescope intermediate focal plane diffuser in front of M2 2-axes gimballed scan mirror FPA optical benches switchable sun diffuser for calibration of solar channels switchable blackbody for IR channels calibration K-mirror image derotator The image principle is based on a fast continuous scan performed from east to west and west to east alternatively and a step like scan in the NS direction to complete the Earth acquisition. The EW and NS scans are performed with a single mirror on a 2-axes gimbaled mount. The spectral channels are in-field separated. A field de rotator is mounted within the telescope to compensate for the image rotation. The imager cooling is driven by the performance of the LWIR channels, especially the CO2 14µm channels. The infrared detectors are cooled down to 50 K with active cryo coolers. Figure 2 illustrates the scanning principle and the optical layout of the FDHSI imager.

Imagery Mission FPA Concept Focal Plane HRFI FDHSI Full dichroic separation Combination of in-field and dichroics separation Cooler Assembly 85 K 50 K SEVIRI like passive (radiative) cooler Active (mechanical) cooler

Imagery Mission Optical Concept Channels BRC Spatial Resolution Mass Power Data rate FHSI 5 5 mn 0.5 / 1km 200 kg 150 W 18 Mb/s FDHSI 13 +4 +4 10 mn 1/ 3km 260 kg 300 W 10 Mb/s mechanical cooler directly mounted on platform FHSI passive cooler sunshield mounted on platform FDHSI Focal Plane & Passive Cooler Assembly mounted on the instrument baseplate Focal Plane in cryostat mounted on the instrument baseplate external baffle fitted to 22°×22° scanning range external baffle fitted to 22°×22° scanning range

Imagery Mission Radiometric Performances HRFI (2-axes scanner) (Example with 85K cold FPA, 536/268 S/N detectors configuration, 4 pixels averaging on IR channels) Radiometric sizing (main features) : Ø300mm aperture slow E/W scan (17s per line) to provide sufficient integration duration with small IFOV large S/N swath (268km) to allow reference imaging within specified BRC (5mn) 85K IR detector cooling (driven by IR-11.4 detector performances) The radiometric resolution specification (noise) are met with margins ×2 for solar channels SNR 20% for IR channels NedT The image principle is based on a fast continuous scan performed from east to west and west to east alternatively and a step like scan in the NS direction to complete the Earth acquisition. The EW and NS scans are performed with a single mirror on a 2-axes gimbaled mount. The spectral channels are in-field separated. A field de rotator is mounted within the telescope to compensate for the image rotation. The imager cooling is driven by the performance of the LWIR channels, especially the CO2 14µm channels. The infrared detectors are cooled down to 50 K with active cryo coolers. Figure 2 illustrates the scanning principle and the optical layout of the FDHSI imager.

Radiometry for FDHSI Radiometric sizing (main features) : Ø300mm aperture E/W scan slowed down to ~3s per line to provide sufficient integration duration with selected detector IFOV 40km S/N swath (32/16 detector array) to allow reference imaging within specified BRC (15mn) 50K IR detector cooling driven by « 14µm » detector performances) The radiometric resolution specifications (noise) are met with margins : > ×1.3 for all solar channels SNR > 20% for all IR channels NedT CO2-14µm performances well below the Threshold NedT and near from Design Goal 0.2K Goal

high diffraction losses for LWIR E/W stretched diamond IFOV Spatial resolution high diffraction losses for LWIR Øtel = 300mm HRFI Mission: (0.5km resolution design goal) The spatial resolution of LWIR channel (IR-11.4) is limited to 1.5km to moderate telescope diameter (Ø300) compatible with imager concept achieving specified radiometric resolution. The specification drives the pixel IFOV the IFOV shall be oversized wrt spatial sampling to damp bouncing above 0.65/ΔX frequency E/W stretched diamond IFOV E/W smearing E/W MTF S/N MTF Proposed approach is based on diamond detector IFOV (MTF damping), E/W stretched (smearing compensation) spatial sampling equal to resolution (SSD= ΔX) Alternative approach is based on twice oversampled raw image and digital filtering of data to control MTF

Infra Red Sounding (IRS) Mission Coverage Repeat cycle Full Disk Coverage 18ox18o 30 min Local Area Cov. 18ox6o 10 min IE = 0.7 @ DX = 6km IE = 0.7 @ DX = 3km

Infra Red Sounding (IRS) Mission DS-FTS: Summary table Main characteristics DS FTS NEΔT Mostly compliant except in SWIR and LWIR Mostly non-compliant Pointing stability Critical: long dwell time Imaging channels VIS/MIR: dichroics TIR: in-field separation No satisfactory solution for the TIR channel Data rate 320 Mbits/s >6Gbits/s: raw data 380 Mbits/s with on-board FFT FPA cooling requirements 0.07 / 0.5 W @ 50 / 80 K (frame rate < 50 Hz) 0.8 / 3.6 W @ 60 / 90 K (frame rate < 2.7 KHz) Optical/thermal Challenging (5 spectrometers) thermal stability critical for spectral calibration Less complex (one interferometer) Spectral Calibration Complex, require excellent channel coregistration Excellent channel coregistration Operability More robust to pixel failure: 0ne dead pixel  loss of one channel - 0ne dead pixel  loss of all channels - Metrology lifetime (laser)

IRS: Synchronous Imaging Requirements Sounder In built Imager Imagery mission Relaxed time co-registration requirement Good co-registration in time/ good correlation Easy to correlate Large collection of data very limited number of channels Larger number of channels Need: Information on ’scene content in sounder pixel General information on characterisation of scene

Infra Red Sounding (IRS) Mission Example of DS optical concept Example of FTS optical concept 5 spectrometers Dwell time ~ 20 ms 4 FT sounding channels Dwell time ~ 8 s MWIR TIR Interferometer Relay Optic Telescope Black Body Imager Telescope VIS / MWIR Imaging TIR MWIR

Infra Red Sounding (IRS) Mission Radiometric Performance (NEDT in K) Dispersive spectrometer Fourier Transform spectrometer DS Noise Specification met except for IRS-1 and IRS-7 LWIR performance strongly dependant on array dark current FTS Noise Specification met only for IRS-3 and IRS-4 LWIR performance strongly dependant on array read-out noise

UV-VIS Sounding (UVS) Mission UVS no direct MSG heritage but from user point of view related to ERS, EPS GOME, ENVISAT SCIAMACHY designed to capture regional, diurnal and sporadic behaviour due to biological, photochemical, and even volcanic factors focus is on spatial scales of 10 km over Europe Coverage Repeat cycle Local Area Coverage 18o NS x6o EW 30 min LAC: Local Area Coverage (placed variable - follow sun illumination) DX=6km@SSP

UV-VIS Sounding (UVS) Mission Spectral Spectral UVS Bands Domain Width Application (nm) (nm) UVS-1 290 – 310 * 0.4 Trace gas retrieval notably stratospheric O3 UVS-2 310 – 328 * 0.4 Trace gas retrieval notably SO2 UVS-3 325 – 335 * 0.4 Trace gas retrieval notably O3 UVS-4 335 – 360 0.4 Trace gas retrieval notably HCHO and BrO UVS-5 420 – 450 0.4 Trace gas retrieval notably NO2 UVS-6A 752 – 757 5 UVS-6B 762 – 770 0.06 Cloud detection, cloud properties, scattering height UVS-6C 772 – 777 5 * Under discussion: - Spectral Width per sample - to request additionally linearly polarised light in two planes with a spectral width of 1 nm over the 290 – 335 nm region (within the UVS-1, UVS-2, and UVS-3 spectral bands)

Lightning Imaging (LI) Mission

LI : Concept description Earth Coverage by 4 Cameras

LI: Optical Design The general configuration of the LMI modules will be very similar to that of the previously studied LFD instrument. It will consist of three main parts: a baffle, the optics (objective and filter) and a detector/proximity electronics housing.

Example of implementation scenario at spacecraft level HRFI FDHSI IRS LI UVS 1100mm 910mm 1350mm Thermal Radiators Stirling Cooler Stirling Cooler Thermal Radiators HRFI FDHSI X Z = North (winter) Y = West (winter) LI Thermal Radiators Cryo-Heatpipes IRS Z = North (winter) Y = West (winter) LI X UVS

Summary This Preliminary MTG instrument concepts have shown a first overview of the possible designs and achievable performances of the 5 Optical Missions planned for the Meteosat Third Generation. All missions present highly challenging performance requirements, which lead to complex and large optical instrumentation. Mission requirements have been extensively reviewed all along the study duration: most of the users needs have been clarified, refined, but some major requirements are still under review by ESA and EUMETSAT, and are being updated in the frame of the coming pre-phase A system study. These modifications might significantly impact the instrument definitions as presented today. For each mission and associated instrument concept, critical areas have been identified. Focal plane array technology is the main development axis for all missions. Associated cooling facilities, and related implications at Spacecraft level are also of concern. The resulting large resources in terms of volume, mass, power and data rate are imposing a multi-platform scenario.