TIMELINE L1b-Preprocessor & CalVal „in a nutshell“ Martin Bachmann Andreas Dietz Thomas Ruppert Tassilo Müller Corinne Frey

TIMELINE – key requirements for calibration Calibration should be consistent with NOAA approach All calibration procedures should be comprehensible and documented Improvements shall be made so that generated time series are consistent in radiometry between AVHRR sensors, and consistent within the lifetime of a single sensor. Reducing bias between AVHRR sensors and drifts in sensor calibration within an AVHRR sensor Flagging radiometric artefacts and errors Account for changes in the spectral response functions between AVHRR sensors Calibration drift ( Spectral inconsistency

 Approach similar to STEVEN et al.  New: using 10 Hyperion scenes (~11 mio pixels) from Greenland to Sahara  Simulation using spectral response curves of each AVHRR sensor  Linear regression to derive band- and sensor-dependent harmonization factors relative to NOAA-19 Spectral harmonization

 System correction: TERASCAN-based  Radiometric calibration: official NOAA-OSPO  linear interpolation inbetween cal.dates  factors in metadata  New: additional harmonization factors based on time series analysis of CEOS sites  Harmonization factors in L1b only in metadata  applied in atm. correction  can be applied by end user to L1b product Radiometric harmonization

Harmonization factors Harmonisation factors are derived using two CEOS desert calibration sites (Lybia 4 and Algeria 3) are cross-checked for CEOS CalVal sites using a “normal” South-European and a Central European test site (La Crau and Demmin) account for multiplicative and additive influences are sensor and time specific are cross-checked to sample scenes of the MERIS 3 rd reprocessing archive are independently cross-checked using the ESA DIMITRI tools and database In addition, the CEOS endorsed extra-terrestrial solar irradiance spectrum by THUILLIER will be used instead of NECKEL & LABS The generation of harmonization factors is based on Apparent TOA reflectance which already accounts for the changing TOA solar irradiance Data normalized to a common spectral response functions “Optimal” pixels: observation angles close to nadir observation times close to solar noon no cloud contamination no vegetation signal – as checked by analysing the NDVI time series

Harmonization of radiometric calibration and different spectral response functions The full harmonization and re-calibration workflow includes the following online and offline processes: 1 st processing using the original NOAA procedures and calibration coefficients as a baseline extract data and metadata for the mentioned CEOS sites extract housekeeping data and metadata of TIR channels offline process: analysis of the generated time series data over CEOS desert sites, generate harmonization factors for every dataset offline process: analysis of the TIR housekeeping data (esp. TIR on-board calibration sources) update metadata for harmonization factors if required: improved system correction for the TIR bands

 Screening of missing and dubious data  Missing lines  Doublicated lines  Odd-even effects  Striping and bad pixels  TIR saturation  Provision of per-pixel quality flags  Provision of scene-based metadata Data quality checks

Summary – TIMELINE L1b approach Libya 4 AVHRR NOAA-19, 2012/07/27 11:42 Algeria 3 AVHRR NOAA-19, 2012/03/06 11:50 CEOS / NOAA CalVal sites Calibration sites Normalized apparent TOA reflectances Harmonized time series Spectral harmonization NOAA-16GainOffset NOAA-17GainOffset NOAA-18GainOffset  Improving radiometric and spectral consistency within single- & multi-sensor time series  Pixel screening & flagging