GSICS “Baseline”

1. GSICS “Baseline” GSICS Executive Panel 2011-06-06

2. Background • Discussion on the subject of GSICS Products and the “Baseline”. • Important we have clear and consistent understanding of these matters • Particularly important as we are developing GSICS Products for the solar channels of GEO imagers and migrate the Products for the IR channels from demonstration to pre-operational status.

3. Philosophical Question • Should GSICS aim to prioritise consistency between Products for different instruments or accuracy of Products for individual instruments? • e.g. GEO VIS: Which method for GPRC/baseline? • If Moon allows 1% cal acc – but not seen by all GEOs • Other methods allow 2% cal acc • IR: Pre-operational ATBDs now converged • Below statements favour consistency • But allow for continuous improvement

4. Proposed Statements 1-5 • GSICS Processing and Research Centres (GPRCs) shall recommend GSICS Products for the satellite instruments for which they have operational responsibility. • GSICS aim for the inter-calibration algorithm implemented by each GPRC to be as consistent as possible for a given class of instrument/channel. To ensure this the ATBDs are defined in a hierarchical structure, based on common general principles. • The ATBDs for each class of instrument are based on a consensus of the best method (or combination of methods) and a common reference instrument. • The finest level of the hierarchical ATBD allows for the specific details of each instrument to be considered. • The GSICS Coordination Center aim to implement a "baseline" algorithm based on the most consistent inter-calibration algorithm for all instruments within a class.

5. Proposed Statements 6-10 • The baseline provides GPRCs with a reference against which they can compare their implementation. • The results of the baseline algorithm for a particular satellite instrument may be considered as official GSICS products upon approval of the GPRC that has operational authority for that instrument. • The development of the baseline algorithm is initiated within GSICS upon GRWG recommendation to, and acceptance of this recommendation by, the Executive Panel. • Developers are encouraged to research further improvements in the algorithms. If these can be shown to be beneficial, a new version of the Product can be released. This shall be accompanied by a new version of the baseline implementation, and other GPRCs implementations. • During a Product's progression through the GSICS Procedure for Product Acceptance, revisions can be made to the baseline by consensus agreement. These should coincide with changes between demonstration, pre-operational and operational status.

6. Discussion • We could define the baseline as either: • As each GPRC’s ATBD for each instrument? • Lowest common denominator?(Hierarchical ATBD truncated as “class” level) • or one GPRC algorithm applied to all GEOs? • If we can improve the ATBD for one instrument: • Need to show not detrimental to others • Then we should revise the baseline ATBD accordingly

7. Need to resolve now • For current GEO-LEO IR products, we’ll be close to converging the individual implementations with GSICS baseline when we go pre-operational • But for solar-band channels we could consider a different mix of methods for each GEO • e.g. not all can use the moon or deserts • The role of the GSICS baseline would then be to provide a consistent reference for internal comparisons • and, potentially, users interested in global consistency • Users want consistent results, not algorithms!

8. Validating Product Consistency • Difficult to directly compare corrected radiances for different satellites • Different SRFs, viewing geometry, ... • But can compare L2 products retrieved from corrected radiances • Observed under same conditions • Need to propagate uncertainties L1->L2 • Possible by some GPRCs operating multiple satellites • Or external users, such as SCOPE-CM projects • Require coordination with these groups during ß-tests