IASI: a Review of Instrument Performance and Characterizations

D. Siméonia, D. Blumsteinb, P. Astruca, C. Degrellea, B. Chetritea, B. Tournierd, G. Chalonb, T. Carlierb, G. Kayalc a ALCATEL SPACE -10 Bd du Midi BP99-06156 Cannes La Bocca Cedex - France, b CNES - 18 avenue Edouard Belin – 31401 Toulouse Cedex 9 – France c EUMETSAT – Am Kavalleriesant 31, D-64295 Darmstadt – Germany d NOVELTIS-Parc Tech du Canal – 2, av. de l’Europe – 31526 Ramonville St Agne Cedex-France

Corporate Communications IASI Payload of the European Meteorological Polar-Orbit Satellites METOP

Mains missions: weather predictions and climate studies. Program led by the French National Space Agency CNES in association with the European Meteorological Satellite Organization EUMETSAT. Prime Contractor: Thales Alenia Space Dimensions of sounder : 1.1x1.1x1.2 m3 Mass sounder < 200 Kg Stiffness > 55Hz during launch Power consumption < 200 Watt Reliability > 0.8 Availability > 97.5 % over 5 years

Status : - EM delivered in Dec 2001 - PFM delivered in July 2003 - FM2 delivered in Dec 2004 - FM3 delivered in Jan 2005 - PFM refurb & delivered in Dec 2006 3

Spectral range continuous from 650 cm-1 to 2760 cm-1 Spectral resolution 0.35 to 0.5 cm-1 Sampling 0.25 cm-1 (8461 samples) Spectral calibration : 10-6 (stability during calibration period) Spectral response knowledge 2-5 % (error < 0.1 K in modelled atmospheric spectra) 280 Radiometric resolution NedT 270 0,8 R1 R2 R3 R4 R55 R66 R7 R88 R99 R100 3 0,7 260

0,6 250

0,5 240 0,4

230 NEDT K 0,3 Température Brillance (K) Température 220 Brightness temp. (K) temp. Brightness 0,2

210 0,1 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 CO2 O3 H2O CO CO2 CO2 CH4 200 Nombre d'ondes (cm-1) N2O 0

Wave number (cm-1) Absolute radiometric calibration : 0.5 K

Step by step scanning

Swath 30 earth views every 8 seconds cycle +/- 50 degrees wrt nadir position Ground swath = 2400 km Stop for measurement period (151 ms) Field motion compensation device

Field Of View Conical: vertex angle = 3.3 ° 4 pixels (12 km on ground at nadir)

Step by step scanning

Swath 30 earth views every 8 seconds cycle +/- 50 ° wrt nadir position Ground swath = 2400 km Stop for measurement period (151 ms) Field motion compensation device

Field Of View Conical: vertex angle = 3.3 ° 4 pixels (12 km on ground at nadir)

Calibration views looked at every 8 s Internal Reference Blackbody view Cold Space view NADIR and 2nd deep space views in External Calibration mode

Beam splitter 5 mm thickness in ZnSe, compensating plate in the fixed arm High performance

equipment Scanning mirror entrance pupil

Fixed corner cube Entrance mirror of Cube corner driving afocal telescope mechanism Compensating ±1 cm stroke plate 423 ms period Mobile corner cube Exi t m i r r o r o f afocal telescope Separating plate Imaging telescope Hollow cube-corner Laser receiver reflectors in Silicon Laser collimator Carbide (170 g) Reference path difference Optical fiber clock

LASER By courtesy of SAGEM source

High stability wavelength reference LASER source Δλ/λ < 10-7 over 5 years (frequency emission locked on a molecular absorption line of an acetylene gas in 1.54 µm region.)

INTERFEROMETER ARMS PAIR UP TO OPTIMIZE FTS CONTRAST IN ORBIT

Global ambient Orbital Model prediction including WFE difference between measurement on one arm component elementary WFE arms optimised by selection of CC and beamsplitter

157nm RMS 1.2µm PTV WFE contrast: 95%

CUBE CORNER SHEAR GRAVITY RELEASE WITHIN 2 µm ACCURACY PREDICTION 8

Output data: Corrected Calibrated Spectrum + Image (1.5 Mb/s) Data compression factor : 40

LF Non Linearity, B1 interferograms B2 interferograms B3 interferograms Cold Space & Filtered Reduced Blackbody interferograms Spectra & Calibration Non Linearity Non Linearity Non Linearity Coefficients from Cold Correction & Spike Correction & Spike Correction & Spike detection detection detection Space and Blackbody Filtered Reduced Spectra (band 3) views Fast Fourier Fast Fourier Fast Fourier Ground Filtered Transform Transform Transform Calibration Reduced Spectra coefficients Initialization Radiometric Radiometric Radiometric & NL determination Calibration Calibration Calibration Algorithms include Band Merging Spectra quality index Coding computation for processing monitoring.

DPS performs corrective action such as interruption of processing or non up-date of the calibration coefficients according to severity error.

The Challenges of the Radiometric Resolution

Optical transmission Interferometer contrast Detector Response Cube Corner Shear 0,8 & WFE Interferometer arms Focal plane temperature NedT [°C] ; Temperature of scene : 280 K 0,7 Water ice absorption 0,6 max at 820 cm-1

0,5

0,4

0,3

0,2

0,1

0 645 845 1045 1245 1445 1645 1845 2045 2245

0,5 0,4 Ground Support Equipment Z306 Blackbody Non Blackness IASI Blackbody 0,3 Martin Black Non Blackness 0,2 0,1 0 -0,1 -0,2 Radiometric Calibration Error in NedT@280 K -0,3 -0,4 HBB 300 K HBB 294 K HBB 280 K HBB 260 K HBB 240 K HBB 220 K Wavenumber (m^-1) -0,5 645 1145 1645 2145 2645

Radiometric calibration measured with OGSE Blackbody using Z306 paint Impact of Z306 Non Blackness on Radiometric Calibration measurements deduced from Equipment Characterization and Environmental Data ± 100 mK Temperature Accuracy After Correction of Ground Support Blackbody Non Blackness 0,5 0,4 0,3 0,2 0,1 0 -0,1 HBB 300 K -0,2 HBB 294 K HBB 280 K -0,3 Radiometric Calibration Error in NedT@280 K HBB 260 K HBB 240 K -0,4 HBB 220 K -0,5 Wavenumber (m^-1) 645 1145 1645 2145 2645

Absolute calibration error almost insensitive to environmental variations such as input and output eclipse

IASI blackbody protected by Design against solar illumination of input and output eclipse

Absolute calibration error almost insensitive to environmental variations such as input and output eclipse

Dedicated testing on ground (Earth and Sun Entrance simulation)

Scan mirror reflectivity variation versus incidence angle almost totally corrected in the frame of the IASI Post Processing

0,5 BEFOREAFTER POST POST PROCESSING PROCESSING 0,4 HBB non blackness zone 0,3 0,3 Spectral band separation 0,2 0,1 00 --0,10,1 RadiometricRadiometric Calibration Calibration Error Error in in NedT@280 NedT@280 KK --0,20,2 --0,30,3 Stare 1 Stare 5 Stare 10 Stare 25 --0,40,4 Stare 25 Stare 10 Stare 5 Stare 1 WavenumberWavenumber (m^-1) (m^-1) --0,50,5 645645 11451145 16451645 2145 26452645

IASI + : the 2nd deep space views allows a flight monitoring of scan mirror reflectivity variations from BoL to EoL

Scan mirror reflectivity variation versus incidence angle almost totally corrected in the frame of the IASI Post Processing

Thermally regulated 80-300 K Blackbody mounting on moving carriage

Measurements of Scan Mirror Reflectivity Law versus Incidence Angle

Validation of Scan Mirror Reflectivity correction

50 mK Calibration Performance Repeatability : 3 IASI flight models (12 tested chains , 3 x 4 pixels) 0,5

0,4

0,3 PFM FM2 FM3 0,2

0,1

-0,1

-0,2

-0,3 Radiometric Calibration Error in NedT@280 K -0,4 Wavenumber (cm-1) -0,5 645 1145 1645 2145 2645 Radiometric Performance from DPS output without Post Processing

ISRF influenced by Pixel Position in the FTS’s Field of Views

100% Outstanding matching 10% between ISRF model and 80% ISRF measurements

60% 0% Measurements at: 40% -10% Wavenumber (m^-1) 2656 2656,5 2657 -1 20% 2655.83 cm (Deuterium Fluoride LASER) 0%

Wavenumber (cm-1) -1 -20% 944.2 cm (CO2 LASER) 2640 2645 2650 2655 2660 2665

ISRF Ghost due to harmonic jitter at 378 Hz

100% ISRF Ghost Work Plan 1,0% Ghost characterization 80% Explanation of Ghost origin

60% 0,0% Identification of Flight Worst Case

40%

Wavenumber (cm-1) -1,0% 2640 2641 2642 2643 20%

Wavenumber (cm-1) -20% 2640 2645 2650 2655 2660 2665

IASI PIXELS : 4 pixels of 12 km at Nadir LOW FIELD RESPONSE DIFFERENCE BETWEEN BANDS

Field response predictions

MaximumSimulations difference and betweenmeasurements bands

Field response measurements (FM3, band 1)

SimulationsDetectors in include pupil plane detector response NU & alignment defaults

IASI has been designed to meet IR sounding mission objectives: Outstanding spectral and radiometric performance Complete and accurate characterization of Instrument Transfer Function

Performances have been optimized for flight conditions based on accurate predictions

IASI achievement: an outcome of a close cooperation with CNES and EUMETSAT

Special thanks to to all people involved in IASI program from industries and space agencies, and in particular to F. Cayla from CNES.

LNR from MAS: 4 pixels x 3 bands DPS A Master Slave System DOB bus Scientific data Processed toward MetOp Raw interferrograms interfero DPCs The master is the Data Management MAS grams Packetised Error report spectra, images, verif. & aux. data FMU Configuration Chain. DMC is in charge of Processing control ICB bus DMC e.g. parameter interfaces with: Setting Channel configuration SW Instrument Management (TMTC) Commands IMS On Board Images Telemetry Imaging Subsystem (image data) IIS Error report Processing METOP (processing data) DPS Subsystem Management In operation DMC controls 8 Processing Chains (DPC)

One DPCs performs processing of interferograms of 3 spectral bands of one pixel.

DPC and DMC boards are based on TSC21020F µprocessors.

By courtesy of SAAB Ericsson Space

High performance blackbody (manufactured by AEA).

Controlled in temperature through its mechanical interface (around 20°C).

Designed and accommodated with care in order to achieve an absolute temperature knowledge better than 0.12 K. By courtesy of AEA Blackbody cavity design: cylinder with a conical base internally painted with Lockeed Martin’s enhanced black finish.

Imaging subsystem [10.3 to 12.5 µm] (manufactured by EADS-SODERN)

Co-aligned with the interferometer optical axis, to perform co-registration of IASI sounder with AVHRR Objectives including spectral filter designed to minimize straylight Microbolometer array U30000A manufactured by BOEING 12 bit video processing chain including offset correction 64x64 images in a 60x60 mrd FOV. Noise Equivalent Temperature Difference 0.5 K (for a scene By courtesy of EADS-SODERN temperature of 280 K). Mass : 5.2 Kg / Power 5.2 W