An Introduction to the MTG-IRS Mission Stefano Gigli, EUMETSAT - PowerPoint PPT Presentation

An Introduction to the MTG-IRS Mission Stefano Gigli, EUMETSAT IRS-NWC Workshop, Eumetsat HQ, 25-07- 13 EUM/MTG/VWG/13/714333 Issue draft 25-07-13

Summary 1. Products and Performance 2. Design Overview 3. L1 Data Organisation EUM/MTG/VWG/13/714333 Issue draft 2 25-07-13

Part 1 1. Products and Performance 2. Design Overview 3. L1 Data Organisation EUM/MTG/VWG/13/714333 Issue draft 3 25-07-13

Meteosat Third Generation (MTG) • The MTG Space Segment consists of two different types of satellites, both 3-axis stabilised, for a total of six satellites : Four Imaging Satellites (MTG-I) • Two Sounding Satellites (MTG-S) • • In full operational capability, 3 satellites will be operated at the same time (2 MTG-I, 1 MTG-S) • First launches: MTG-I1: 2018 • MTG-S1: 2020 • MTG-I2: 2023 • • The IRS flies on board MTG-S EUM/MTG/VWG/13/714333 Issue draft 4 25-07-13

The Infrared Sounder • Scope of the MTG-IRS mission is providing the user community with high spatial and temporal resolution information on the vertical distribution of humidity and temperature, as well as on their horizontal distribution • Humidity and temperature profiles will be generated on the vertical hybrid-sigma coordinates of the ECMWF forecast system (91 levels) • The requested horizontal resolution is 4 km at nadir • The data rate must be such that the entire Earth Disc is covered in one hour EUM/MTG/VWG/13/714333 Issue draft 5 25-07-13

From Level 1 to Level 2 • These products are the result of a sequence of processing steps, that produce different data levels (L0, L1, L2 ...) • The vertical profiles of temperature and humidity are L2 data, that can be obtained by manipulating spectral radiance data with high spectral resolution • This means that L2 processing the IRS has to provide a set of Spectrum Vertical profiles spectra (at Level 1), along the entire Earth disc • The L2 algorithms will convert these spectra into vertical profiles, by exploiting the physical laws that govern radiation transfer EUM/MTG/VWG/13/714333 Issue draft 6 25-07-13

The Level 1 Data • The IRS produces 3D data; two dimensions, the horizontal ones (latitude and longitude) are the same for both L1 and L2 data; the difference is in the third dimension, which represents: a spectrum at Level 1 • a vertical profile at Level 2 • • This also means that an IR spectrum must be generated for every spatial element of the Earth disc • A single spectrum is also named a spectral sounding; so the L1 products of the IRS are a collection of IR spectral soundings • In conclusion: The IRS L1 data are a 3D set with two spatial and one spectral dimension • This means that the IRS must be an imaging spectrometer • EUM/MTG/VWG/13/714333 Issue draft 7 25-07-13

Spatial Coverage & Repeat Cycle • The Earth disc is split in 4 Local Area Coverage (LAC) Zones • Numbered from South to North LAC 4 • Hence LAC1 is South Africa and LAC4 is Europe (strange shape LAC 3 needed to cover Canary Islands) LAC 2 • 1 LAC covered in 15min (so the entire Earth can be theoretically LAC 1 covered every hour) • But LAC4 is revisited every 30min EUM/MTG/VWG/13/714333 Issue draft 8 25-07-13

Spectral Performances • The spectral range and resolution are dictated by the needs on vertical resolution at L2, resulting in a spectrum that entirely lies in the IR region, between 680cm-1 and 2250cm-1 (4.44  m to 14.7  m), more exactly: • split in two non contiguous LWIR MWIR bands: 680cm-1 to 1210cm-1 ( LWIR band ) • 1600cm-1 to 2250cm-1 ( MWIR • band ) • with a spectral resolution of 0.625cm-1 EUM/MTG/VWG/13/714333 Issue draft 9 25-07-13

Part 2 1. Products and Performance 2. Design Overview 3. L1 Data Organisation EUM/MTG/VWG/13/714333 Issue draft 10 25-07-13

IRS Inputs and Outputs Earth Radiance The IRS collects the radiation emitted by the Earth and produces as IRS output a set of spectra How does it work? L1b data (measured spectral radiance) EUM/MTG/VWG/13/714333 Issue draft 11 25-07-13

Fourier Transform Spectrometry The IRS is a: Earth Radiance Fourier Transform Spectrometer (FTS) That means: OPTICS The Earth IRS 1. radiation is focused on a focal plane Focusing Optics EUM/MTG/VWG/13/714333 Issue draft 12 25-07-13

Fourier Transform Spectrometry The IRS is a: Earth Radiance Fourier Transform Spectrometer (FTS) That means: The Earth radiation is OPTICS 1. focused on a focal IRS plane Where it is directly 2. detected in the time domain Focusing Optics Detection EUM/MTG/VWG/13/714333 Issue draft 13 25-07-13

Fourier Transform Spectrometry The IRS is a: Earth Radiance Fourier Transform Spectrometer (FTS) That means: The Earth radiation is OPTICS 1. focused on a focal IRS plane Where it is directly 2. detected in the time ELECTRONICS domain The signal is handled 3. by an analogue chain Focusing Optics and eventually digitised Analogue Detection Electronics EUM/MTG/VWG/13/714333 Issue draft 14 25-07-13

Fourier Transform Spectrometry The IRS is a: Earth Radiance Fourier Transform Spectrometer (FTS) That means: The Earth radiation is OPTICS 1. L1b data focused on a focal IRS plane Where it is directly 2. detected in the time ELECTRONICS domain The signal is handled 3. by an analogue chain FFT Focusing Optics and eventually digitised Analogue A Fourier Transform (FFT) is Detection 4. Electronics carried out to get the spectrum EUM/MTG/VWG/13/714333 Issue draft 15 25-07-13

Interferometry Problem: Earth Radiance Light is an e.m. wave, but not a radio wave! Even in the IR the OPTICS L1b data frequency is too high IRS (up to 67 THz , that is 0.015 ps wave period) ELECTRONICS for being followed by any man made detector FFT Focusing Optics (not to mention energy issues) Analogue Detection Definitely not a working design! Electronics EUM/MTG/VWG/13/714333 Issue draft 16 25-07-13

Interferometry Earth Radiance Classical solution: OPTICS L1b data IRS Scale down the frequency by interferometry and generate interferograms ELECTRONICS FFT Focusing Optics a Michelson interferometer is introduced in the optical path Analogue Detection Electronics EUM/MTG/VWG/13/714333 Issue draft 17 25-07-13

Interferometry Earth Radiance Classical solution: OPTICS L1b data Interferometer IRS Scale down the frequency by interferometry and generate interferograms ELECTRONICS FFT Focusing Optics a Michelson interferometer is introduced in the optical path Analogue Detection This is the core of IRS Electronics EUM/MTG/VWG/13/714333 Issue draft 18 25-07-13

Space vs. Ground Processing The processing Earth Radiance load is too high for being handled by the on-board processing alone OPTICS L1b data Interferometer IRS ELECTRONICS FFT Focusing Optics Analogue Detection Electronics EUM/MTG/VWG/13/714333 Issue draft 19 25-07-13

Space vs. Ground Processing The processing Earth Radiance load is too high for being handled by the on-board processing alone OPTICS L1b data Interferometer IRS SS It must be split ON-BOARD between ELECTRONICS Space Segment On-board FFT Focusing Optics (SS) and Processing Ground Segment Analogue IRS GS Detection (GS) Electronics EUM/MTG/VWG/13/714333 Issue draft 20 25-07-13

Infrared Technology: Cooling Working in the IR Earth Radiance has disadvantages: The detector must be cooled OPTICS (actually at 60K) L1b data Interferometer IRS SS and the nearby ON-BOARD optics as well ELECTRONICS (a bit less cold) On-board Cooled FFT Processing Focusing Optics Analogue Cooled Detection IRS GS Electronics Assembly EUM/MTG/VWG/13/714333 Issue draft 21 25-07-13

Infrared Technology: Radiometric Calibration However, despite cooling: Earth Radiance A residual thermal offset background adds up to Blackbody the signal; it must be OPTICS removed L1b data Interferometer IRS SS Two deep space views are then exploited ON-BOARD (not shown here) ELECTRONICS An internal Blackbody On-board Cooled FFT must be introduced Processing Focusing Optics Analogue Cooled Detection IRS GS Electronics Assembly EUM/MTG/VWG/13/714333 Issue draft 22 25-07-13

Infrared Technology: Radiometric Calibration However, despite cooling: Earth Radiance A residual thermal offset background adds up to Blackbody the signal; it must be OPTICS removed L1b data Interferometer IRS SS Two deep space views are then exploited ON-BOARD Calibration (not shown here) ELECTRONICS An internal Blackbody On-board Cooled FFT must be introduced Processing Focusing Optics and everything must be Analogue Cooled Detection IRS GS Electronics Assembly calibrated (on ground) EUM/MTG/VWG/13/714333 Issue draft 23 25-07-13

Imaging Features The IRS has to be Earth Radiance an imaging spectrometer Blackbody Hence it must have a OPTICS spatial discrimination L1b data Interferometer IRS SS capability ON-BOARD Calibration This is achieved ELECTRONICS using two matrix On-board Cooled detectors : FFT Processing Focusing Optics • one for LWIR Analogue Cooled Matrix • one for MWIR IRS GS Electronics Detectors EUM/MTG/VWG/13/714333 Issue draft 24 25-07-13