GRWG Report

1. GRWG Report Tim Hewison 1 November 2012

2. Outline • Status Updates – For Information only • GEO-LEO IR • GEO Solar • Lunar • Archive Re-Calibration Products • IEEE TGARS Special Issue • Instrument Event Logs • GRUAN • Issues for Exec Panel decisions • Statement on GSICS-GRUAN interaction • Chairing GRWG • Procedure for GSICS Membership

3. GEO-LEO IR (1) • Most of the GSICS Corrections for the infrared channels of current geostationary imagers are now in demonstration mode. • NOAA and EUMETSAT hope to have the products for the GOES and MSG series promoted to pre-operational status during Fall 2012. While these are mature products, they are subject to limitations - in particular the range of time over which they are valid. • Many GEOs suffer from diurnal variations in the calibration - and in particular during the period around local midnight. These are being addressed by the development of a method to transfer the inter-calibration reference over more of the diurnal cycle, initially using Aqua/AIRS to transfer the calibration from Metop-A/IASI.

4. GEO-LEO IR (2) • GRWG have also been preparing a framework to allow the transfer our inter-calibration reference instrument from Metop-A/IASI to Metop-B/IASI by calculating "Delta Corrections", based on double-differences of the GSICS Corrections calculated using each independently. • This is complemented by CNES' plans to perform comparisons of Metop-A/IASI and Metop-B/IASI by a number of different methods to account for the unavailability of simultaneous collocated observations due to the orbital configuration.

5. GEO-LEO IR (3) • The common format developed for the GSICS Corrections by GDWG have allowed a new plotting tool to be developed to generate GSICS Bias Monitoring, by reading the contents of the netCDF files directly from the GSICS servers. • The same tool can be used to generate and compare inter-calibration products from different instruments generated by different GPRCs. • This has required extensive interaction with GDWG to define additional attributes in the netCDF files to allow the conversion of the results into brightness temperatures, which are more meaningful to the users than the radiances used in the calculation.

6. GEO Solar (1) • Development work has continued to focus on inter-calibration for the channels of the current geostationary imagers in the reflected solar band. • Outline ATBD was produced by Dave Doelling (NASA), • based on comparing statistical distributions of the reflectances of Deep Convective Clouds (DCCs) observed from the GEO imagers • and MODIS, as an inter-calibration reference instrument. • EUMETSAT are currently implementing this algorithm. • NASA are preparing centralised processing of MODIS data • to generate statistics of the reference instrument, • which will be commonly used for all GEO imagers.

7. GEO Solar (2) • Members of GRWG have also been involved in a review of the Saharan desert sites currently used as calibration reference targets. • The spatial, temporal and spectral variability of different sites has been analysed to quantify the uncertainties associated with their use, and potentially to reduce this by refining the site selections. • This has included a dedicated workshop on the Libya #4 site, coordinated by IVOS. • GRWG to investigate potential use of GOME/SCIAMACHY hyperspectral observations to validate models and/or as an inter-calibration reference for solar band channels.

8. Lunar Several GRWG members have been investigating the Moon as a calibration transfer reference for Geostationary imagers channels in the reflected solar band although it is also applicable to LEO instruments. GRWG has encouraged USGS to set up an online facility to provide irradiance predictions from their ROLO model customised for specific observations of various instruments, accounting for their viewing geometry and spectral response. GRWG has encouraged NIST to consider tying the current lunar irradiance models to SI-traceable standards, Would allow lunar observations to provide useful absolute calibration (at present their application is practically limited to detecting calibration trends and inter-channel differences).

9. Archive Re-Calibration GRWG identified need for new class of inter-calibration product: to provide a consistent calibration for whole datasets from different satellite instruments to generate Fundamental Climate Data Records. These Archive Re-Calibration products will complement existing products, which have mostly focused on near real-time applications. Examples now in demonstration mode: PATMOS-x product for AVHRR (A)MSU inter-calibration products, developed at NOAA EUMETSAT are also developing inter-calibration products for the Meteosat archive, using various HIRS instruments as references.

10. Special issue of IEEE Transactions on Geoscience and Remote Sensing on the Inter-Calibration of Satellite Instruments proposed jointly by GSICS and IVOS including four guest editors from GRWG. When published, in early 2013, this special issue will provide a valuable reference to the inter-calibration community, bringing together a large collection of papers focusing on this topic. These include many from GRWG authors, covering the generation, validation and analysis of various GSICS products, as well as an extensive overview of inter-calibration techniques. Papers can be made Open Access – at a price (US$3000) IEEE TGARS Special Issue

11. EUMETSAT activities on Calibration Event Logging • Achievements to date: • Set-up of an internal EUMETSAT Working Group on Calibration Event Logging after a recommendation from CGMS and GSICS  Focus = log any event capable of affecting data quality and calibration • Assessment of the current logging systems available at EUMETSAT • Draft of the concept for a calibration event logging system  database providing information on: • Mission • Irregular Events • Processing Events • Data Outages • Contribution to be presented at the CGMS meeting 40 (CGMS-40 EUM-WP-09) • Next steps forward: • Ask CGMS + GSICS partners to review of the proposed concept • Formulation and formalization of the user requirements • Regular reporting to the internal EUMETSAT Climate Monitoring Coordination Group • Incorporate feedback from internal + external users into the database • Iteration through GSICS with external partners to refine the system before deployment GSICS Research & Data Working Group to provide advice and support for standard definitions and reporting

12. GRUAN (GCOS Reference Upper Air Network) Representation at GRUAN Expansion Workshop • Participation in group writing white paper on sat cal/val • Emphasis on quality, not quantity of radiosondes • Launches timed for satellite overpasses • Can select sites where these are synoptic hours (0z, 12z) • Real-time evaluation of representativeness errors • Based on observed variability in space & time • 3-way interaction for validation of L2 products • e.g. UTH (w/ SCOPE-CM/CMSAF)

13. Proposal by GSICS-EP-13 for a Statement on GSICS-GRUAN interaction (1) Why would it be good to have such a statement? • the relationship between GSICS and GRUAN is being addressed at various meetings. And generally speaking, perception and perspectives are not aligned. • therefore a general statement reflecting the standpoint of GSICS could be helpful for reference in future discussions.

14. Proposal by GSICS-EP-13 for a Statement on GSICS-GRUAN interaction (2) Proposal for a formulation: The GSICS Executive Panel sees potential for mutual benefits of GRUAN and GSICS activities. The EP wishes to stress that the benefit is clearly mutual. Therefore coordinated activities in specific areas are recommended (an example is presented on the following slide).

15. Proposal by GSICS-EP-13 for a Statement on GSICS-GRUAN interaction (3) Example for mutual benefit: GRUAN measurements could provide improved input data for radiative transfer simulations of the high resolution radiance spectra at the top-of-the-atmosphere , those spectra can be compared with hyperspectral satellite measurements (e.g. AIRS and IASI). • Differences between measured and calculated spectra should in principle be the same for all GRUAN stations under the assumption that the measurements are stable (this is a very valid assumption) and that GRUAN stations have the same bias errors (this is to be shown) • Thus, GSICS would provide via the hyperspectral satellite measurements a ‘travelling reference standard’ for GRUAN stations. • It is understood that the realisation of such benefits requires coordination between GSICS and GRUAN, for instance the launching of radiosondes sufficiently close to a satellite overpass.

16. GRWG Chairing - Suggestion: Identify specific roles to be covered by vice-chairs of GRWG e.g. Grouped by Product Class Development of GSICS Products for Solar Band GEOs LEO-LEO products Developing methods for Archive Re-Calibration Or grouped by spectral band: Thermal Infrared Reflected Solar Band (incl. Ocean Colour?) Microwave Other Issues: Chairing GRWG

17. Expansion of GSICS from a GRWG perspective the main issue is additional need for resources to keep up with the additional needs/expectations and the science development GRWG asks the GSICS EP to provide firmer guidance There are already some firm rules/constraints for membership Adherence to scope of GSICS, Commitment for free & open exchange, Developing inter-calibration products for their instruments tying to GSICS standards… Procedure for Membership application Other Issues: Expanding Membership