THE VEGA 2000 data set description of data properties draft

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/imag
  es/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.cne
s.fr8080/
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.fr80
80/system/content.htmlperfos
6
GENERAL DESCRIPTION
7
VEGETATION onboard SPOT 4
8
The VEGETATION instrument
9
Radiometry specs calibration
10
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
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.fr8080/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 lt 0.1 km multitemporal lt 0.3
  km
• absolute location 0.5 km registration with
  HRVIR lt 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
Consequence on temporal superimposition
Observed location of AVHRR pixels in a time
series, after D. Meyer, IJRS
29
observed geometric stability
S10 NDVI product

• S1 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
  parameters from 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 lt 80
40
Water mask

• Strait of Messina

41
Content of data set
Total volume per pixel 16 bytes

• Users manual

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
Thats all folks(for today!)