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THE VEGA 2000 data set description of data properties (draft)

THE VEGA 2000 data set description of data properties (draft). Compiled by E. Bartholomé, JRC Ispra. SOURCES of INFORMATION. Main sources of Information. The VEGETATION portal : http://www.spot-vegetation.com The VEGETATION web site at CNES: http://vegetation.cnes.fr

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THE VEGA 2000 data set description of data properties (draft)

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  1. THE VEGA 2000 data set description of data properties(draft) Compiled by E. Bartholomé, JRC Ispra

  2. SOURCES of INFORMATION

  3. Main sources of Information • The VEGETATION portal : http://www.spot-vegetation.com • The VEGETATION web site at CNES: http://vegetation.cnes.fr • the Users Guide: http://www.spotimage.fr/data/images/vege/VEGETAT/book_1/e_frame.htm • Henry & al 2000: VEGETATION image performances, (Belgirate) • Passot 2000: VEGETATION image processing methods in the CTIV (Belgirate) • Saint 1998: the VEGETATION Programme

  4. Technical description of the system VEGETATION homepage at CNES: http://vegetation.cnes.fr:8080/

  5. The users manual On-line:http://www.spotimage.fr/data/images/vege/VEGETAT/book_1/e_frame.htm stand-alone downloadable version: http://vegetation.cnes.fr:8080/system/content.html#perfos

  6. GENERAL DESCRIPTION

  7. VEGETATION onboard SPOT 4

  8. IMAGE SPECTRAL BANDS : Blue - Red - NIR - SWIR (Red, NIR and SWIR identical to HRVIR ones) CODING : 10 bits OPTICS : telecentric lenses F.O.V. : 101° (ground swath = 2250 km) DETECTION : CCD line array RESOLUTION : 1.165 X 1.165 km² The VEGETATION instrument

  9. Radiometry: specs & calibration

  10. Blue Red NIR 0.14 0.6 SWIR Typical vegetation reflectance 0.12 Typical soil reflectance 0.5 0.10 0.4 0.08 Relative response Reflectance 0.3 0.06 0.2 0.04 0.1 0.02 0.00 0 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 Wavelength Main specs of the VEGETATION system - radiometry • Four spectral bands • Blue 0.43 - 0.47 µm Near InfraRed 0.78 - 0.89 µm • Red 0.61 - 0.68 µm ShortWave InfraRed 1.58 - 1.75 µm G. Saint, 1998

  11. Main specs of the VEGETATION system - radiometry • Calibration • interband and multitemporal : better than 3% • absolute : better than 5% through: * on-board calibration device to measure evolution with time *calibration campaigns Henry & al, 2000 - Belgirate

  12. Calibration methods • Pre-flight measurements (absolute) • On-board calibration lamp (multitemporal and multi-angular) • Vicarious calibration over test sites (absolute) • Calibration over the Rayleigh scattering (absolute) • Calibration over desert sites (multitemporal and multi-angular) • Calibration over the sun glint (interband) • Calibration over clouds (interband) • Calibration over snowy sites (multi-angular) • VGT/HRVIR intercalibration using simultaneous viewing (Henry & al. , Belgirate, 2000)

  13. Evolution of sensor sensitivity Henry & al, 2000 - Belgirate

  14. Sensor calibration: an example Henry & al, 2000 - Belgirate

  15. Sensor calibration: overall conclusions • Absolute calibration : • B0 : 4% - B2 : 4% - B3 : 5% - SWIR : ? • Multitemporal calibration : • better than 2% • Interband calibration : • B2/B3 : 2% - B2/B0 : 3% - B2/SWIR : ? • Intercalibration with HRVIR • B2 : 3% - B3 : 2% - SWIR : 2% Henry & al, 2000 - Belgirate

  16. SWIR defective detectors Brazil - 23 May 99 Blue/NIR/SWIR The MIR sensors Henry & al, 2000 - Belgirate

  17. The MIR sensors • InGaAs CCDs are sensitive to protons (irradiation tests carried out in 1999) • Radiation effects: detector dark current increases and becomes unstable Henry & al, 2000 - Belgirate

  18. Instrument resolution

  19. Main specs of the VEGETATION system - reolution • Spatial resolution 1km in the entire field of view • Off nadir observations up to 50°

  20. Stable across-swath ground resolution G. Saint, 1998

  21. Spatial resolution: pre-flight MTF measurement http://vegetation.cnes.fr:8080/system/mtf.htm

  22. Spatial resolution: in-flight FTM measurement MTF estimation using simultaneous HRVIR image as reference: Very good consistency with pre-flight measurements Henry & al, 2000 - Belgirate

  23. Actual effect of angular viewing on resolution Dec 3, 1999: close to swath edge Niger Delta, Dec 1, 1999: close to nadir

  24. Product geometry

  25. Main specs of the VEGETATION system - geometry • Distorsions : • multispectral < 0.1 km multitemporal < 0.3 km • absolute location ~ 0.5 km registration with HRVIR < 0.3km

  26. The VEGETATION geometric correction (1) • A) Straight geometrical modelling that takes into account • the satellite location • computed from an orbit bulletin (MADRAS) • or from real time on board navigator (DORIS), • attitude movements • computed from the gyrometers data • instrument geometrical characteristics,(measured before launch, and recalibrated in orbit): • the payload positioning on SPOT4 • the 4 cameras positioning on the payload • the pixel viewing directions, taking into account the lenses distorsion (see next slide), specific for each camera • Geometrical modelling is made for the B3 band • Other bands pixels are located by difference to B3 (dl,dp) Passot, 2000 - Belgirate

  27. The VEGETATION geometric correction (2) • B) Manual and assisted GCP pointing (from March 99) to fix the absolute satellite attitude error • From a 3650 GCPs data base • built from VEGETATION image chips previously pinpointed with SPOT HRV images. • Seasonal effects are taken into account • Attended operations : • selection of 10 to 20 GCPs per orbit, chosen on non cloudy locations • or propagation to the next orbit of the computed bias Passot, 2000 - Belgirate

  28. Expected accuracy for VEGETATION IFOV Multitemporal Field of View • Registrations • Multispectral : <0.2 km • Multitemporal : <<0.5 km for one year • Absolute location <0.8 km 1 km G. Saint, 1998 Consequence on temporal superimposition Observed location of AVHRR pixels in a time series, after D. Meyer, IJRS

  29. observed geometric stability S1 NDVI product S10 NDVI product

  30. Principle of data mapping • Map projection in Plate-Carrée : • Elevation corrections using a Digital Elevation Model (ETOPO5), interpolating between the 2 location grids at 0 and 5000m elevation • Cartographic coordinates computed with the Geolib IGN library • Bicubic interpolation on a 4x4 window Map Projected area 1km step Raw data 1.15 to 1.6 km step Passot, 2000 - Belgirate

  31. Computing ground reflectances

  32. Computation of TOA reflectance • Normalization using parameters computed in QIV (cf calibration methods) • Interpolation of bad detectors : SWIR blind or defective detectors • Radiance computed using absolute calibration parametersfrom QIV • Reflectance computed with a solar irradiance model, taking into account sun angles, and sun-earth distance • Computation of TOA NDVI for temporary use in the synthesis process Passot, 2000 - Belgirate

  33. Atmospheric correction • Using the SMAC CESBIO software : a simplified implementation of 6S, tuned for VEGETATION spectral bands • Using water vapor data : short term forecasts, 4 deliveries/day from Meteo-France • Using climatology of ozone (CESBIO) • Using simple static models for aerosols (CESBIO) • Using a 8km resolution DEM for pressure estimation • Atmospherical parameters are calculated on 8km x 8km cells, then interpolated / pixel Passot, 2000 - Belgirate

  34. Case study: the VEGA 2000 data set

  35. Geometric properties of the VEGA 2000 data set Coverage of the global window: Upper left: -180°,75° Bottom right: 180°,-56° Projection: lat-long (“plate-carrée”) Ellipsoid: WGS 84 Pixel size: 1/112 DEG = 0.0089285714 image size: 40320 x 14673 pixels (global coverage)

  36. Accurate data georeferencing

  37. S1 Daily coverage Saint 1998 Distance between 2 successive paths at equator: 375 km

  38. S1: areas of overlap Combination based on NDVI max

  39. Varying coverage extension in N. latitudes 1-10 Jan 2000 1-10 Jul 2000 Sun azimuth angle must be < 80°

  40. Water mask Strait of Messina

  41. Content of data set Users manual Total volume per pixel: 16 bytes

  42. Data coding (1) Reflectance channels (B0, B2, B3, Mir) NDVI Users manual

  43. Data coding (2) Users manual

  44. Users manual

  45. Status map

  46. Status map Users manual

  47. That’s all folks…(for today!)

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