GERB2-GERB 1 transition: discussion item

1. GERB2-GERB 1 transition: discussion item J E Russell Imperial College, London j.e.russell@imperial.ac.uk

2. GERB data after 10th May 2007 • On 10th May 2007 the GERB 2 (MET-8) Edition 1 record will stop. Edition data from GERB 1 (MET-9) is not expected to be released until spring ’08. • NRT processing of the GERB 1 data will continue and be accessible from RMIB but will not initially be deemed suitable for scientific work. • The intention is to validate the GERB 1 data for an edition release around spring 2008. • This initial release will be considered separate from the GERB 2 dataset as for the Edition 1, work to tie the two GERB data sets together will not be completed.

3. GERB data after 10th May 2007 • We raise 2 points for discussion: • What is the appropriate status and accessibility of the NRT prior to validation? • We have the opportunity to make some changes to the operational processing of the data prior to its release as edition data and associated freezing of the software, we expect to make small changes to product contents and QA procedures that won’t affect the science values. There are also proposals to make more major changes but need to discuss a user perspective on the desirability of this. • GERB 1 validation strategy: • To follow the GERB 2 model, would ideally process our GERB-CERES overlap datasets collected in 01/06/06 – 30/06/06 and 19/01/07 – 10/02/07, with the operational software setup and produce the quality summary on this basis. • If major processing updates are agreed on, ideally these should be implemented first separately from the operational system and process these periods with it so that the effect could be diagnosed before implementing operationally (is this possible?)

4. GERB processing after 10th May 2007 • The swap will be used as an opportunity to include some improvements in the processing. Expected minor improvements (no impact on science values) include: • Additions to the automatic quality checks and data exclusions • Additional fields in the products, such as pixel level flags and angle information • Proposed moderate improvements, (additional science values, no change to science values that already exist) • Correction to only exclude actual glint conditions, i.e. glint angle over ocean only, as opposed to currently glint angle for all scenes • Possible filling of the glint region, if the inclusion of pixel level flags allow it to be clearly identified • Possible significant changes to the processing (changes to existing science values): • improvements to the cloud flags (IR flag to help sunglint issue) • Changes to radiance to flux conversion • Improvements to clear sky ocean unfiltering • Addition of a snow / ice ADM

5. Advantages/disadvantages changes • Major changes would provide the best possible products at the time from GERB 1 measurements, but would make the record different from the GERB 2 data • The implementation of the changes may make the NRT data very difficult to use, as they would causes a series of changes to this processing affecting the science values, these are not always easier to identify from the product names. • Additional complication that SEVIRI will change a definition of their IR radiances in April 08, this has a 3% effect on one SEVIRI channel. +/- 5% uncertainty in SEVIRI radiances are allowed for in GERB accuracy but such a change could result in a jump in the record that couldn’t be addressed by reprocessing until SEVIRI reprocessed. (will affect LW unfiltering and radiane to flux conversion