Compact High Resolution Imaging Spectrometer (CHRIS) Mike Cutter (Mike_Cutter@siraeo.co.uk)
Summary CHRIS Instrument Design Instrument Specification & Performance Operating Modes Calibration Plan Data Processing
Instrument Design
System Level Architecture Optical Input PROBA PLATFORM Telescope Spectrometer Electronics AOCS Payload Processing Unit Data Handling System Telemetry & Command TM & TC Users Ground Station (Redu) Spectral Sira
Functional Block Diagram Telescope Spectrometer IMAGER CCD CCD Drive Electronics Digitisation ELECTRONICS Command Handling Data Formatting Power Conditioning Command Interface Data Interface
Optical Design # Patented design, low cost, capable of extension to SWIR
FOCAL PLANE ASSEMBLY
CHRIS
Specification & Performance
Specification Image area Spatial sampling interval Spectral range (nominal) Spectral resolution 18.6km x 18.6km (748 x 748 pixels) 25 or 50m 415nm to 1050nm 1.25 to 11nm Spectral registration ± 0.06 pixels Spatial registration ± 0.05 pixels Straylight Gain stage Digitisation 1% total for an extended source 4 levels (albedo 0.5,1,2,4 levels) 12 bits Signal-to-noise ratio 200 (@ target reflectance 0.2, 25m, 10nm)
Specification continued Data per (19x19 km 2 ) image 131 Mbits (16.4Mbytes) Number of images per orbit nominally 5 (81.9Mbytes) Power consumption < 10 W primary power Mass < 14 kg Volume 790 x 260 x 200 mm 3
MTF (ACROSS-TRACK) - 546 nm Across-track MTF - 546nm & columns 60, 380 & 700 1 0.9 0.8 0.7 MTF 0.6 0.5 0.4 Col 60 Col 380 Col 700 0.3 0.2 0.1 0 0 2 4 6 8 10 12 14 16 18 20 Spatial frequency c/mm
Responsivity CHRIS Radiometric Calibration (G=3) 160000 Digital signal (ADU) for radiance of 1W/m^2/str/nm 140000 120000 100000 80000 60000 40000 20000 0 400 500 600 700 800 900 1000 1100 Wavelength nm
Wavelength Calibration WAVELENGTH CALIBRATION 1100.00 1000.00 900.00 WAVELENGTH nm 800.00 700.00 600.00 500.00 400.00 0 20 40 60 80 100 120 140 160 180 COLUMN NUMBER
Spectral Resolution SPECTRAL RESOLUTION AT 446 nm SPECTRAL RESOLUTION AT 546 nm SPECTRAL RESOLUTION AT 910 nm 1.2 1.2 1.2 1 1 1 NORMALISED RESPONSE 0.8 0.6 0.4 NORMALISED RESPONSE 0.8 0.6 0.4 NORMALISED RESPONSE 0.8 0.6 0.4 0.2 0.2 0.2 0 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 WAVELENGTH nm 0 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 WAVELENGTH nm 0 880 890 900 910 920 930 940 WAVELENGTH nm Wavelength FWHM 446 nm 1.9 546 nm 3.6 910 nm 10.6
Operating Modes
Multi-view CHRIS Data CHRIS will be able to acquire 5+ near-simultaneous views of any site
Platform Constraints Platform Pointing Along-track 0, ± 25º, ±44º pitch (@ ground) Across-track <= +/-30º (@ ground) Pointing Specification Absolute pitch/roll/yaw < +/- 0.1º Control of pitch/roll/yaw < +/- 0.015º/s (11% of imaging pitch rate) Maximum pitch rate 0.5º/s Observations baseline Motion compensation (approx. x3) Five images per observation orbit per day
Imaging Modes Earth Imaging Full swath @ 25m or 50m (nadir equivalent) Image 18.6 x 18.8 km Half swath @ 25 or 50m (nadir equivalent) Image 9.3 x 18.8 km Dark Imaging Eclipse observations Flat Fielding In-orbit solar calibration (yaw steer - limited aperture) Observation of ground calibration sites Internal LED source Wavelength calibration Selected ocean scene
Maximum number of spectral bands Name Across-track sampling distance @ nadir (number of image pixels) Along-track sampling distance @ nadir Maximum number of spectral bands per image line Full swath 25x25m 25m (748) 25m 18 + 1 Full swath 50x25m 50m (374) 25m 27 + 1 Full swath 50x50m 50m (374) 50m 61 + 1 Half swath 25x25m 25m (374) 25m 38 + 1 Half swath 50x25m 50m (190) 25m 52 + 1 Half swath 50x50m 50m (190) 50m 117 + 1 NB. One spectral band will be used for smear correction.
Calibration Plan
In-flight Calibration Flat field (monthly TBD) In-orbit solar calibration (yaw steer - limited aperture) Internal LED source Ground calibration sites DC Offsets (per observation orbit TBD) Dark reference pixels (located at side of CCD image area) Smear pixels (located at ends of CCD image area) Over-scanned pixels Eclipse observations (plus temperature monitoring) Wavelength (monthly TBD) Oxygen absorption band @ 760nm
Routine Health Checks Offset & average dark signal levels Dark field non-uniformities Response non-uniformities Temporal noise Absolute spectral response Linearity
Data Processing Plans
Observational & Data Aspects Ground Station Receive data packets Transmit image & ancillary data Monitor satellite health Archive data PROBA Platform Recieve requests Schedule platform manoeuvres Command CHRIS Store image data Transmit to ground Ground Station Uplink requests Sira Format data Radiometric correction Wavelength correction Data validation Transmit data to users Arcive data sets Sira Collate & check requests Prepare configuration files Review scheduling options Transmit files to Redu User Processing Geo-correction Atmospheric correction Algorithm implementation Validation with ground site data Publication of results User Requests Longitude/Lattitude/Altitude Pointing requirements & limits Number of imaging lines Observation time (day/night) Spectral & spatial configuration Motion compensation level (tbd)
Processing Related Activities @ Sira Validation & preparation of observing requests first level sanity checks of user requests generation of instrument configuration files etc. Level 1a data processing acquire data sets (1-4 weeks after observations) radiometric correction wavelength calibration (tbd) routine instrument health checks Production of data sets for users Supply data sets to users (1 week turn around) Format (tbd)