KNMI, The Netherlands * SCIAMACHY validation workshop, Bremen, 6 Dec ‘04 Large scale validation of SCIAMACHY nadir reflectance Gijs van Soest *, L. Gijs Tilstra, Juan Acarreta, Piet Stammes

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Outline Reflectance validation –Known issues –Method and data Large data set validation New key data: an improvement?

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 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

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 UV reflectance spectrum

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Known issues of UV reflectance Radiometric calibration: reflectance is 20% too small –Also in other channels –Showstopper for non-DOAS retrievals (O 3 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

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 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

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Large scale validation: method & data Inputs for RTM: –Cloud mask based on FRESCO –GOME ground albedo data base –O 3 profiles IFE limb retrieval (FTP server) TOMS v8 climatology using TOSOMI O 3 columns –Temperature and geopotential height from ECMWF 1100 states between 09/2003 and 12/ states between 04/2004 and 08/2004

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Histograms of SCIA/RTM-1 (2004) Ozone TOMS v8 climatology Small signal: extremely sensitive to calibration Fraunhofer lines O 3 profile Spread depends on polarization east

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Map of : nm

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Map of : nm SA A

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 w/ IFE limb O 3 profiles: nm gradient Problem in ozone profiles

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Difference map 2003: nm ESRIN orbits CHANNEL 1 DATA FROM ESRIN NRT ORBITS ( SCI_NL__1PNPDE* ) PRIOR TO MARCH 2004 SHOULD NOT BE USED!

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Effect of decontamination: nm Signal for < 300 nm is so small that reliable calibration is a real problem decontamination: orbits

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 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

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Reflectance: comparison with MERIS Spectral averaging of SCIA, spatial averaging of MERIS. Orbits 2509/2510 old several versions of new

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Reflectance: comparison with RTM DAK Sahara state from orbit 2509 KNMI polarization correction Rest as in other SCIA/RTM study

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Regular key data: (SCIA/5.00) NASA sphere key data:  strong unphysical spectral features

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Regular key data: (SCIA/5.00) Spectralon key data:  offset smaller, but unphysical spectral features remain

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Channel Sahara state Channel 3 Spectralon NASA sphere V5.00 Increased noise Feature in channel overlap Feature

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 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) –Don’t use ESRIN NRT Ch1 data before 03/2004!!!

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 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

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Characterisation of validation method albedo cloud fractionviewing angle orbit number

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Histograms of SCIA/RTM-1 (2004) Ozone TOMS v8 climatology west

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Map of : nm

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Channel Sahara state Channel 2 Spectralon NASA sphere V5.00 Feature

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Channel Sahara state Channel 4 Spectralon NASA sphere V5.00 Channel overlaps still unsolved Feature

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Channel Sahara state Channel 5 Spectralon NASA sphere V5.00 Increased noise

Gijs van Soest, SCIAMACHY validation workshop, 6 Dec ‘04 Channel Sahara state Channel 6 Spectralon NASA sphere V5.00 Increased noise + feature Increased noise + feature