1. 1 © Crown copyright 2003 GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 User Requirements for GRAS SAF RO Products Dave Offiler

2. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 2 © Crown copyright 2003 Background Generic (technology-free) URs for temperature & humidity profiles traceable to WMO/CBS Reviewed by APM (“Granada-1”), GRAS SAG, CLIMAP & GRAS SAF 1st User Workshop Also feedback from URs for other RO missions (WATS, ACE+) Adapted for constraints of RO technique and in particular the GRAS on Metop mission, via the EURD URD specifies general & specific requirements on GRAS SAF data products.

3. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 3 © Crown copyright 2003 Main Drivers - NWP Objective: Short to medium range weather forecasting (hours to a few days) F/c initialisation fields optimum wrt true state of atmosphere (assimilation) Rapid availability of global observational data Quality control to maintain a priori expected error characteristics (Gaussian, zero bias) Errors well characterised

4. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 4 © Crown copyright 2003 Main Drivers - Climate Objective: detect & monitor long-term climate change Long duration, continuous data sets with homogeneous, global coverage; diurnal effects unaliased Long-term stability (no bias drift) Accurate temperature & humidity profiles Monthly (or annual) grid box means (Level 3) Validation of CGMs Initialisation of CGMs from NWP (re-)analyses

5. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 5 © Crown copyright 2003 Atmospheric Layers WMO Definition of Atmospheric Layers

6. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 6 © Crown copyright 2003 GRAS Mission Observation Requirements (NWP)

7. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 7 © Crown copyright 2003 GRAS Mission Observation Requirements (Climate)

8. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 8 © Crown copyright 2003 Products & Processing Profiles of corrected refraction (bending angles) - Level 1b Profiles of refractivity - Level 2a Profiles of temperature, humidity & pressure - Level 2b For climate, use of a consistent processing methodology (re-processing whole mission) For NWP, availability in NRT (<3hrs)

9. GRAS SAF User Workshop Helsingør, Denmark, 11-13 June 2003 9 © Crown copyright 2003 User Requirements Document URD is a base document in the GRAS SAF documentation tree - almost all other documents flow from it. SAF operational performance will be judged against the URD URD contains much more detail than presented here, including specific requirements, cross-referenced elsewhere URD is stable but not fixed; can evolve in a controlled way Real user feedback on URD (or products defined by it) are always welcome