GRWG Web Meeting 2018-09-13

Planning a GSICS/CEOS-WGCV Workshop on SI-traceable reference instruments

Agenda of Web Meeting

  1. Tim Hewison (EUMETSAT) - Introduction to the web meeting
  2. Bruce Wielicki (NASA) – Ideas for Technology Development Needs - oral presentation only
  3. Constantine Lukashin (NASA) – Inter-calibration requirements/algorithms for the VIS/NIR
  4. Dave Tobin (SSEC) - IR inter-calibration requirements - oral presentation only
  5. Peng Zhang (CMA) - Development of Chinese SI-traceable reference instruments and retrospective recalibration of historical satellite data
  6. Chuanrong Li/Lingling Ma (AOE) - Cross-calibration through spaceborne SI-traceable reference instruments
  7. Nigel Fox (NPL) - Requirements for uncertainty analysis & Traceability issues
  8. All - Workshop Aims, Chairing and Logistics


AOE: Lingling Ma, Yongguang Zhao, Ning Wang, Caixia Gao

CMA: Peng Zhang, Xiuqing Hu, Na Xu, Chengli Qi, Ling Wang, Yong Zhang, Hanlie Xu, Yuan Li, Shuai Gao, Ling Sun

EUMETSAT: Tim Hewison (Chair), Sebastien Wagner, Viju John

JMA: Masaya Takahashi, Yusuke Yogo and Kazuki Kodera

KMA: Dohyeong Kim, Minju Gu

NPL: Nigel Fox, Paul Green, Emma Woolliams

NASA: Bruce Wielicki, Constantine Lukashin, Dave Johnson

NOAA: Fred Wu, Fangfang Yu, Larry Flynn, Manik Bali

USGS: Tom Stone

U.Colorado/LASP: Greg Kopp, Peter Pilewskie

U.Leicester: Gary Corlett

U.Miami: Peter Minnett

U.Reading: Rhona Phipps (FIDUCEO project coordinator)

U.Wisc/SSEC/CIMSS: David Tobin

Introductory Presentations

Tim Hewison (EUMETSAT) introduced the web meeting, explaining how it aims to define the aims of the workshop and encourage participants to focus on the desired outcomes.

Bruce Wielicki (NASA) described how the original requirements for CLARREO were driven by climate change detection, and that this would be a key economic benefit of such a system by providing early confirmation and precise quantification of the magnitude of change, which could lead to faster action being taken. He provided an update on the plans for CLARREO Pathfinder, which is now in Phase A with a launch planned for 2022. Preparation for the use of this mission could form a focus of the workshop. Bruce proposed a key outcome of the workshop could be to develop a white paper documenting the societal benefits of SI-traceable Reference Instruments.

Constantine Lukashin (NASA) presented the general requirements to use such an instrument to inter-calibrate instruments with channels in the reflected solar band and an overview of an algorithm to do this. He suggested one topic for the workshop could be how to design trade-off studies to optimise the use of reference instruments for different applications.

Dave Tobin (UW/SSEC/CIMSS) described the application of reference instruments to inter-calibrate IR instruments, including imagers and sounders. His opinion was that the technology needed for IR is now sufficiently mature - although this was questioned for the RSB. He emphasised the importance of completely characterising and documenting the reference sensor and suggested a key outcome of the workshop could be to define what information is needed in such documentation. He also highlighted the benefit of having key decision makers from EO satellite agencies present at the workshop - at least for the initial presentations, which should focus on the benefits to end users.

Peng Zhang (CMA) introduced a joint project of several Chinese agencies to develop reference instruments to target climate change detection, inter-calibration and recalibration in the future. The importance of providing free and open access to instruments’ data and documentation was discussed - especially if they are to be considered as international references. Peng explained that data is available through CMA’s data portal (

Action A.GRWG.20180913.1: Peng Zhang (CMA) to circulate details of access to CMA’s data availability and any limitations.

Lingling Ma (AOE) reviewed the algorithms used to inter-calibrate different instruments to reference instruments, and explained the concepts of using reference instruments to characterise PICS, including RadCalNet. She emphasised the need to characterise more sites, covered a broader range of geography and surface types - and for rigorous uncertainty analysis. She suggested the following workshop topics:
  • Trade-offs in the use of PICSs as reference transfers

  • How to involve the various research groups through WGCV and GSICS, how to facilitate cooperation amongst them and promote research work on SI-traceable reference transfer calibration?

  • How to carry out comparisons between multiple spaceborne SI-traceable reference instruments and reach a consensus, promoting international cooperation?

The latter stimulated an interesting discussion, where it was suggested that the EO community should build on the methods developed by international metrology labs.

Nigel Fox (NPL) followed up this suggestion, highlighting the value of having multiple references and performing regular comparisons among them to ensure century-long stability and the importance of comprehensive uncertainty analysis to support SI traceability . He introduced the FIDUCEO project, explaining how measurement equation diagrams had been developed to communicate uncertainty analyses.

Survey results were reviewed and lead a wide-reaching discussion ensued, in which the following were proposed:

Workshop Aims
  • To document the needs for SI-traceable Reference Satellite Instruments and the societal benefits

  • To seek consensus agreement on how to evidence traceability through reference instruments

  • To review the current state of the art in development of SI-traceable Reference Instruments technology and inter-calibration algorithms

Key Outcomes
  • A white paper on the needs for SI-traceable Reference Satellite Instruments, highlighting the societal benefits for a range of application areas

    • The body of this could form the basis of paper in EOS Transactions or BAMS

    • Appendices could be detail uncertainty analysis

  • A document defining what characteristics of SI-traceable Reference Satellite Instrument need to documented

  • Climate Requirements

  • Instrument design - RSB and IR

    • Including current status, unresolved issues and uncertainty analysis

    • Including spectral calibration and polarisation sensitivity

  • Inter-calibration algorithm - RSB and IR

  • Characterisation algorithm - PICS and Moon

  • Inter-comparison of Reference Instruments

    • In-orbit verification of SI-traceability
  • Use of Reference Instruments to improve operational sensors

  • Mostly plenary

  • Possible break-outs to develop outcome documents for different application areas


Agreed attendance should be open to all, but the following should be specifically targeted:

  • WGCV and GSICS members

  • End Users

    • Including Weather, Climate, Land and Ocean communities

  • Industry

  • Decision makers at programme level in EO satellite agencies


Agreed the workshop should take place in Europe

  • Noting the limitations for agency travel

  • NPL and EUMETSAT have offered to host

  • 3 or 3.5 days

  • In Fall 2019

  • International SI-traceable Reference Satellite Instrument Workshop

    • To be agreed by

  • An organising committee was nominated, initially comprising of:

    • Nigel Fox (NPL)

    • Bruce Wielicki (NASA)

    • Greg Kopp (U.Colorado/LASP)

    • Xiuqing (“Scott”) Hu (CMA)

    • Tim Hewison (EUMETSAT)

  • The next meeting of organising committee was proposed for November 2018 to allow announcements and invitations to be circulated in good time.

  • The composition of the organising committee will be confirmed at the next meeting.

  • Please contact Tim Hewison if you are interested in joining the organising committee.

Action: A.GRWG.20180913.2: Tim Hewison (EUMETSAT) to set up next organising committee meeting.
Topic revision: r19 - 15 Sep 2018, TimHewison
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