1. 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

2. 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

3. 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 ox6o min
‘Rapid Scan’ 6ox6o /3 min
0.5 km 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 ( 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.

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

5. 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 ox18o min
Local Area Cov. 18ox6o /3 min
1 km 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.

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

7. 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

8. 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]

9. 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

10. 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.

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

12. 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
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

13. 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.

14. 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

15. 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

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

17. 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 / / 80 K
(frame rate < 50 Hz)
0.8 / / 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)

18. 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

19. 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

20. 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

21. 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 min
LAC: Local Area Coverage
(placed variable - follow sun illumination)

22. 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)

23. Lightning Imaging (LI) Mission

24. LI : Concept description
Earth Coverage by 4 Cameras

25. 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.

26. 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

27. 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.