MTG Design

Meteosat Third Generation (MTG) will be based on three axis stabilised platforms, the instruments will be pointed at the Earth for 100% of their in-orbit time.

The satellite series will comprise four imaging and two sounding satellites. These satellites will no longer be stabilised by the spinning of the platform, as this was the case for first two generations of Metosat satellites, but by three axis stabilised platforms.

The satellite platforms will host instruments that will scan and probe (FCI, LI an IRS) the Earth surface and the atmosphere with additional channels and better spatial, temporal and radiometric resolution.

The imaging satellites, MTG-I, will fly the Flexible Combined Imager (FCI) and the Lightning Imager (LI), an imaging lightning detection instrument.

The sounding satellites, MTG-S, will include an interferometer, the Infrared Sounder (IRS) and the Sentinel-4 instrument, the high resolution Ultraviolet Visible Near-infrared (UVN) spectrometer.


Flexible Combined Imager

The Flexible Combined Imager (FCI) on the MTG-I satellite will continue the very successful operation of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on Meteosat Second Generation (MSG).

Figure 1
Figure 1: FCI instrument in at test centre. Credit: ESA

Requirements for the FCI have been formulated by regional and global Numerical Weather Prediction (NWP) and Nowcasting communities.

These requirements are reflected in the design which allows for scanning the full Earth disc in 10 minutes in support of the Full Disc Scanning Service (FDSS), or the upper quarter of the disc (i.e., Europe) in 2.5 minutes in support of the Rapid Scanning Service (RSS).

To support the Full Disc Scanning Service (Figure 2), the FCI measures in 16 channels in the visible and infrared spectrum of which eight are placed in the solar spectral domain between 0.4 µm to 2.2 µm, delivering data at a 1 km spatial sampling distance (resolution) at nadir (sub-satellite point the centre of the disc). The additional eight channels are in the thermal spectral domain between 3.8 µm and 13.3 µm, delivering data at 2 km spatial sampling distance at nadir.

To support the Rapid Scanning Service (Figure 3), the FCI samples two channels in the solar domain (0.6 µm and 2.2 µm) at higher spatial sampling distance of 0.5 km. and two channels in the thermal domain (3.8 µm and 10.5 µm) at higher spatial sampling distance of 1 km at nadir.

Figure 2: Animation of the FCI scanning pattern in support of the Full Disc Scanning Service (FDSS)
Figure 3: Animation of the FCI scanning pattern in support of the Rapid Scanning Service (RSS)

Figures 4-6 illustrate the variation of average pixel area in km2 for imagery with 1 km spatial sampling distance at nadir, and approximate pixel contours for four selected locations in Europe.

Figure 4
Figure 4: Approximate pixel area in km 2 of FCI imagery with 1 km spatial resolution at nadir.
Figure 5
Figure 5: Approximate pixel area in km 2 of FCI imagery with 1 km spatial resolution at nadir, over Europe
Figure 6
Figure 6: Pixel projections for FCI imagery with 1 km spatial resolution at nadir, for four selected locations, using a Transverse Mercator projection.

The FCI takes measurements in 16 channels, of which eight are placed in the solar spectral domain between 0.4 µm to 2.2 µm, delivering data with a 1 km spatial resolution.

The additional eight channels are in the thermal spectral domain between 3.8 µm to 13.3 µm, delivering data with a 2 km spatial resolution.

In the RSS mode two channels in the solar domain will be disseminated with advanced spatial resolution of 0.5 km. In the thermal domain two channels will have an advanced spatial resolution of 1 km. The scanning domain is the so-called LAC4 domain, with the wider Europe region enclosed.

Instrument information
Channel Centre Wavelength Spectral Width Spatial Sampling Distance (SSD)
VIS 0.4 0.444 µm 0.060 µm 1.0 km
VIS 0.5 0.510 µm 0.040 µm 1.0 km
VIS 0.6 0.640 µm 0.050 µm 1.0 km; 0.5 km*
VIS 0.8 0.865 µm 0.050 µm 1.0 km
VIS 0.9 0.914 µm 0.020 µm 1.0 km
NIR 1.3 1.380 µm 0.030 µm 1.0 km
NIR 1.6 1.610 µm 0.050 µm 1.0 km
NIR 2.2 2.250 µm 0.050 µm 1.0 km; 0.5 km*
IR 3.8 (TIR) 3.800 µm 0.400 µm 2.0 km; 1.0 km*
WV 6.3 6.300 µm 1.000 µm 2.0 km
WV 7.3 7.350 µm 0.500 µm 2.0 km
IR 8.7 (TIR) 8.700 µm 0.400 µm 2.0 km
IR 9.7 (O3 ) 9.660 µm 0.300 µm 2.0 km
IR 10.5 (TIR) 10.500 µm 0.700 µm 2.0 km; 1.0 km*
IR 12.3 (TIR) 12.300 µm 0.500 µm 2.0 km
IR 13.3 (CO2 ) 13.300 µm 0.600 µm 2.0 km

Note: The channels VIS 0.6, NIR 2.2, IR 3.8 and IR 10.5 are delivered in both FDSS and RSS sampling configurations, the latter is indicated by * in the table.

With the FCI on board the MTG-I satellites, Europe will continue to play the leading role in imaging radiometry from the geostationary orbit in the decades to come.

Lightning Imager

Figure 7
Figure 7: Structural model of the Lighting Imager. Credit: ESA

The Lightning Imager (LI) provides a real time lightning location and detection (cloud-to-cloud and cloud-to-ground lightning, with no discrimination between the two types).

The imager is a new instrument, not based on any previous heritage from the Meteosat Second Generation series.

The LI uses detector elements arranged in a detector array covering the whole Earth (no scanning mechanism).

The total energy received from the photons are sensed by each detector element and integrated during the integration period. These are then compared with the LI Trigger Threshold and if the energy exceeds this threshold, it is identified as an LI triggered Event.

The Lightning Imager (LI), on board the MTG-I satellites, will continuously measure at a wave-length of 777.4 nm with a very narrow bandwidth, with a spatial resolution 4.5 km at sub-satellite point, triggered by a variable threshold — optical pulses initiated by lightning emitting energy of larger than between 4 and 7 µJm-2sr-1.

Figure 8
Figure 8: Field of view of the Lightning Imager instrument

The field of view (FOV) of the LI instrument is covered by four identical cameras on the instrument, each covering one out of four domains on the observable Earth disc.

Products derived from the instrument data will be arranged around following three categories:

  1. Events — what the instrument measures, a triggered pixel in the detector grid.
  2. Groups — neighbouring events in the same integration period (1 ms), representing a lightning stroke.
  3. Flashes — collection of groups in temporal and spatial vicinity (XX km, YY milliseconds), representing a lightning flash.

The MTG-I LI instrument will complement the NOAA Geostationary Lightning Mapper (GLM) on the GOES-R and the GOES-S satellites and CMA Lightning Mapper onboard the FY-4 satellite series.

Figure 9
Figure 9: LI product categorisation

Infrared Sounder (IRS)

Figure 10
Figure 10: Structural model of the IRS. Credit: ESA

The Infrared Sounder (IRS) on MTG-S will be able to provide information on horizontally, vertically, and temporally (4-dimensional) resolved water vapour and temperature structures of the atmosphere.

The IRS acquires a number of spectral soundings simultaneously over a dwell using a two dimensional detector array. It uses a ‘step-and-stare’ mechanism to probe the Earth´s atmosphere.

The dwell coverage is stepped in an east/west direction to form a line of dwell spectral soundings, before moving northward to form the next line, covering the local area coverage (LAC) within the repeat cycle duration (‘step-and-stare’ principle of probing the atmosphere).

Four separate LAC zones are defined and scanned sequentially (Figure 8). One LAC is acquired within 15 minutes, consisting of overlapping dwells following a step and stare scan pattern. Each dwell consists of 160x160 pixels (spectral soundings), with 4 km spatial sampling distance at nadir. Europe (LAC4) is observed every 30 minutes

Figure 11
Figure 11: MTG Infrared Sounder dwell coverage

The spectral soundings are transmitted to the ground as interferograms and transformed to spectral channels as part of the ground processing, before dissemination to the end users as Level 1 datasets.

The IRS is based on an imaging Fourier-interferometer with a hyperspectral resolution of 0.625 cm-1 wave-number, taking measurements in two bands, the Long-Wave Infrared (LWIR) and the Mid-Wave Infrared (MWIR).

Summary of technical specifications:

  • Two Spectral bands: MWIR: 1600 to 2250 cm-1 (4.44–6.25 µm) and LWIR: 680 to 1210 cm-1 (8.26–14.70 µm).
  • Full disc coverage in 60 min, Europe region (Local Area Coverage) 30 min.
  • Spatial resolution of 4 km x 4 km at nadir.
  • Radiometric measurement ranges between 180 K and 313 K (equivalent black-body temperature.)
  • Spectral radiometric noise (excluding spectral calibration) at 280 K black body: between 170 and 900 mK depending on the considered wave-number inside the band of interest.
Figure 12
Figure 12: Illustration of IRS expected weighting functions

The IRS includes the ozone band within LWIR and the carbon monoxide band within MWIR. This will allow measurement within the free troposphere, leading to information on enhanced levels of pollution in the boundary layer below.

MTG Sounding Service

Ultraviolet, Visible and Near-Infrared (UVN)

Figure 13
Figure 13: Instrument spectral bands and sampling domain

The Ultraviolet, Visible and Near-Infrared (UVN) sounding instrument is a Copernicus Sentinel 4 instrument designed for geostationary chemistry applications. It will fly on board the MTG-S satellites.

The UVN is a spectrometer measuring in the ultraviolet (UV: 305–400 nm), the visible (VIS: 400–500 nm) and the near infrared (NIR: 750–775 nm), with a spatial sampling distance of around 8 km.

Its observations are restricted to European area coverage, from 30 to 65º N in latitude and 30º W to 45º E in longitude, depending on seasonality (Figure 10). The observation repeat cycle period will be approximately one hour.

Further Services

Geostationary Search and Rescue (GEOSAR) relay

MTG will carry a small communications payload (GEOSAR) to relay distress signals of 406 MHz beacons to a central reception station in Europe, which passes the signals on for quick organisation of rescue activities. The geostationary relay allows a continuous monitoring of the earth disc and immediate alerting.

Data Collection and Retransmission

MTG will provide a Data Collection and Retransmission service to collect and relay environmental data from automated data collection platforms, including surface, buoy, ship, balloon or airborne platform.

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