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Large scale validation of SCIAMACHY nadir reflectance

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Large data set validation. New key data: an improvement? ... Data from Sep Dec 2003, Apr Aug 2004, decontaminations excluded ... – PowerPoint PPT presentation

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Title: Large scale validation of SCIAMACHY nadir reflectance


1
Large scale validation of SCIAMACHY nadir
reflectance
  • Gijs van Soest, L. Gijs Tilstra, Juan Acarreta,
    Piet Stammes

2
Outline
  • Reflectance validation
  • Known issues
  • Method and data
  • Large data set validation
  • New key data an improvement?

3
Reflectance and irradiance validation
  • Errors in reflectance cause errors in geophysical
    parameters retrieved from it
  • Spot and characterize possible problems in
    SCIAMACHY level 1 data
  • Instrument, calibration data, algorithms
  • Approach compare measured and calibrated UV
    spectra with radiative transfer calculations
  • Single states careful, detailed characterization
  • Large data sets spot drifts, possible
    geographical seasonal trends

4
UV reflectance spectrum
5
Known issues of UV reflectance
  • Radiometric calibration reflectance is 20 too
    small
  • Also in other channels
  • Showstopper for non-DOAS retrievals (O3 profile)
  • Spectral feature associated with polarization
  • Near 350 nm BrO and CHOH retrieval affected
  • Improved in recent (V5.0x) data
  • Spectral stray light, memory effect

6
Large scale validation method data
  • Comparison of SCIA nadir reflectance spectra with
    RTM LIDORT
  • Data from Sep Dec 2003, Apr Aug 2004,
    decontaminations excluded
  • 4 substates per state East, East-C, West-C,
    West
  • Wavelength range 250 400 nm or 270 340 nm
  • NRT SCIA L1B data (SCI_NL__1PN)
  • Processor version 4.0x in 2003, 5.0x in 2004
  • L1C using SciaL1C tool, all calibrations on

7
Large scale validation method data
  • Inputs for RTM
  • Cloud mask based on FRESCO
  • GOME ground albedo data base
  • O3 profiles
  • IFE limb retrieval (FTP server)
  • TOMS v8 climatology using TOSOMI O3 columns
  • Temperature and geopotential height from ECMWF
  • 1100 states between 09/2003 and 12/2003
  • 9400 states between 04/2004 and 08/2004

8
Histograms of SCIA/RTM-1 (2004)
east
Ozone TOMS v8 climatology
9
Map of ltSCIA/RTM-1gt 320-340 nm
370-390
10
Map of ltSCIA/RTM-1gt 270-290 nm
11
w/ IFE limb O3 profiles 270-290 nm
12
Difference map 2003 270-290 nm
CHANNEL 1 DATA FROM ESRIN NRT ORBITS
(SCI_NL__1PNPDE) PRIOR TO MARCH 2004 SHOULD NOT
BE USED!
13
Effect of decontamination 270-290 nm
decontamination orbits 12031-12208
Signal for ? lt 300 nm is so small that reliable
calibration is a real problem
14
New radiometric key data set
  • Based on measurements from the PI period, IFE
    have calculated new radiometric key data
  • Two sets Spectralon and NASA sphere
  • Irradiance now more or less OK (w/in 5 from
    reference in UV/Vis/NIR)
  • Assess quality of reflectance with new KD

15
Reflectance comparison with MERIS
old
Spectral averaging of SCIA, spatial averaging of
MERIS. Orbits 2509/2510
several versions of new
16
Reflectance comparison with RTM DAK
Sahara state from orbit 2509 KNMI polarization
correction Rest as in other SCIA/RTM study
17
Regular key data (SCIA/5.00) NASA sphere
key data
? strong unphysical spectral features
18
Regular key data (SCIA/5.00) Spectralon
key data
? offset smaller, but unphysical spectral
features remain
19
Channel 3
2509 Sahara state Channel 3 Spectralon NASA
sphere V5.00
20
Conclusion (1)
  • Large scale comparison between SCIA and RTM
    suited for finding geographical/slowly varying
    features in data
  • Flexible tool, possible to include several data
    sources
  • No temporal trends found technique may be used
    for degradation monitoring
  • Ch 1 extremely sensitive to calibration (low
    signal)
  • Dont use ESRIN NRT Ch1 data before 03/2004!!!

21
Conclusion (2)
  • New IFE Key Data investigated
  • Irradiance looks reasonable
  • Reflectance offset improved
  • Many spectral features introduced
  • Reflectance is sometimes very noisy
  • Alternative use current key data and correct the
    reflectance with a smooth function based on
    validation result
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