page 1 validation workshop, 6.12.04, ife bremen, g. lichtenberg:calibration status national...

Validation Workshop, 6.12.04, IfE Bremen, G. Lichtenberg:Calibration status

National Institute for Space Research

SCIAMACHY Calibration status November SCIAMACHY Calibration status November '04'04

G. Lichtenberg et al.

SRON - National Institute for Space ResearchUtrecht, The Netherlands



Outline

Radiometric calibration Polarisation status Light Leak Dark correction Evolution Bad & Dead Pixel mask Summary of PCRs Verification Other open points Conclusions



Radiometric calibration (I)

History: Reflectance comparisons showed an offset of -15 to -20% SMR comparison showed an irradiance 8 – 15 % too high It was decided to re-calculate radiometric key data on basis

of different measurements (NASA sphere & OPTEC msm's) TPD and IfE re-calculated ABSRAD and ABSIRR, both results

agreed IfE found a deviation of the EL_AZ parameter (Limb mirrors)

and BRDF and provided a correction IfE calculated correction factors to be applied on OPTEC5

calibrated data and key data on a full wavelength grid solving some interpolation problems.



Radiometric calibration (II)

2 types of radiometric key data from IfE are available:

NASA sphere based Spectralon based

Both key data sets were corrected for Memory effect, Non-linearity, Spectral stray light (SRON) In-flight NDF (SRON/IfE) Correction of integration time in the IR (SRON) Relative angle correction BRDF (TPD)



Radiometric calibration (III)

Verification method: SRON processed (new) verification orbits with L0->1

processor provided by DLR for both IfE keydata sets and the original key data set

L0 files with SMR measurements close to the verification orbits are processed for both keydata sets and the newly calculated SMR is extracted by SRON

KNMI and RAL verify reflectances



Radiometric calibration (III)

Verification: Comparison of solar irradiances with Kurucz show

agreement within 3-5% for all channels except channel 1 (reason unclear) and channels 7,8 (ice)

Comparison done by KNMI with different solar reference show a 5% offset in channel 5

Comparison with reflectance model by KNMI shows good agreement for wavelengths from 320nm – 390 nm for Spectralon based key data

RAL will compare SCIA reflectances with GOME reflectances Comparison with MERIS shows the 1-7 % offset in the range

between 450nm - 900nm



Radiometric calibration (IV)

Old key data (result by G. v. Soest & G. Tilstra (KNMI))



Radiometric calibration (V)

'NASA' key data (result by G. v. Soest & G. Tilstra (KNMI))



Radiometric calibration (VI)

'Spectralon' key data (result by G. v. Soest & G. Tilstra (KNMI))



Radiometric calibration (VII)

Meris comparison (J. Accareta, KNMI)



Radiometric calibration (VIII)

Open points & Schedule: RAL verification for wavelengths above 380 nm Difference of BRDFs calculated with NASA and Spectralon

data above 750nm (possibly external stray light) For the next verification round (early 2005) Spectralon key

data will be used Reasons for spectral features in Spectralon key data Baseline (to be tested on Level2):

ASM Diffuser spectra for DOAS type retrieval ESM Diffuser spectra for retrieval where radiometric accuracy

is needed



Polarisation (I)

Summary of polarisation calibration and application: s/p and -45/+45 polarisation sensitivity were measured Ratio of science detectors to PMD signal for different

polarisation directions were measured The discovery of the phase shift made it necessary to

derive some parameters theoretically. IfE described a possible method in IfE-TN-211299 based on Mueller Matrices

This document was used to define algorithms to generate a set of key data

The DP uses the key data to define Mueller Matrices and thus calculating a polarisation correction factor



Polarisation status (II)

History: After tests by J.M. Krijger showed some sign problems in the

polarisation a common polarisation reference frame was defined in June '03

Greek key data and data processor were adjusted accordingly, solving some, but not all problems

Additional investigations by TPD showed 2 errors in IfE-TN-211299. A new set of key data was generated (current version).

These key data show some unphysical values in PMD1 and the PMDD/45 combination (used to determine U) does not work

IR polarisation determination is still hampered by transmission problems



Polarisation (III)

Further planning: Key data side:

Check of IfE-TN by J. Skupin (IfE) After check TPD will compare their algorithms to the findings

and if necessary recalculate the key data once more If no serious errors are found, new key data can be provided

very soon DP side:

all parties together that work currently on polarisation verification have to come together to review the current knowledge and define methods to find possible errors in the DP

KNMI (P. Stammes) and SRON will organise this



Light Leak

Results so far (analysis by R. v. Hees (SRON)): Analysis based on February '04 Limb dark measurements Channel 7 shows a light leak with an amplitude between 20

and 120 BU/s The intensity distribution shows no spectral features The light leak changes amplitude rapidly and not very

predictably (the 1σ value is up to 49 BU/s) No simple correlation with orbit phase was found Further investigations are under way



Light Leak (II) - AmplitudeR

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Light Leak (III) - VariationR

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RO

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Dark correction (I)

Proposal by ESA for orbital dark correction means: NRT data will have a dark correction from data taken 14

orbits earlier OL data will have correct dark subtraction This is only an issue for channels 7&8 at times the

transmission is varying Proposal by ESA for correction dark variation over

orbit PCR33 (which asks for the inclusion of transmission

variation) will not be implemented in this round, but later Details have to be worked out This is mostly an issue for channel 8



Evolution of Bad & Dead Pixel Mask (I)

Investigations by Q. Kleipool showed: The Bad & Dead Pixel Mask (BDM) is not static, i.e. over

time the number of bad & dead pixels increase The likely cause is radiation damage by protons or other

heavy particles (only gamma ray radiation was tested on-ground due to budget limits)

The long term development is not yet clear The changing BDM can influence retrievals in the IR

severely SRON is capable of calculating a BDM for each orbit after

SODAP Currently it is investigated how a dynamic mask can be

implemented in the operational processor chain



Evolution of BDM (II)

Development of BDM over last 8000 orbits: Channel 6: increase by 35 pixels to 90 pixels total Channel 7: increase by 100 pixels to 380 pixels total Channel 8: increase by 95 pixels to 275 pixels total

One dead or bad pixel at the wrong position in a fitting window can change retrieval results significantly

Apart from a dynamical BDM mask a L2 fit window monitoring has to be implemented to change a fit window if too many bad pixels make retrieval impossible.

TN available at www.sron.nl/~SCIA_CAL (go to the 'Documents' page).



Evolution of BDM (III)



Evolution BDM (IV)



Summary PCR (I)

The following L0->1 PCRs will be implemented in '04:

New Memory Effect & Non-linearity Orbital darks Availability of all solar spectra for L2 applications Flagging of data taken during decontamination Correction of integration times channel 6-8

Later implementation: Throughput correction (this might be reversed when it is

needed for a slitfunction correction).



Summary PCRs (II)

PCRs were implementation in '04 is unclear/will not implemented:

Slitfunction correction (ice): SAST group will work o this Light Leak chanel 7 : No implementation soon, no correction

available Spatial stray light: No implementation soon, no correction

available Key data PCRs

Implementation of new radiometric KD possible (in time for reprocessing), if Level2 validation shows no major problems

Implementation of new polarisation key data possible (however it is not clear that this is needed)



Verification (I)

The following combinations of DP/key data will be calculated for verification orbits

Old DP/Old key data Old DP/New radiometric key data New DP/New keydata

Keydata versions Radiometric: Spectralon key data, NDF in-flight Polarisation: 3.1 Nadir + 3.0 Limb MEC/NL: New values for new correction Other: unchanged



Verification (II)

Schedule: Originally planned: L1 verification workshop 16.12.04 No longer possible because IECF was not ready in time New plan: Verification workshop early next year (January or

February)



Other points

Other calibration issues: DLR-IMF will work on an ice slitfunction correction within

SAST Corrections for memory effect, non-linearity and IR

integration time were implemented in the DP Transfer of knowledge for key data will start soon



Conclusions The verification of radiometric calibration was done The polarisation correction is currently checked Light Leak in channel 7 proves difficult to correct Details of the implementation of a dynamical BDM

have to be discussed Verification data will be available soon Depending on Level2 results, new key data can be

implemented Calibration documents and more available at

www.sron.nl/~SCIA_CAL/