Satellite Instrument Pre-and Post-Launch Calibration WS, December 2013, Italy
A recommendation to establish a permanent Task Force for satellite sensor calibration comes from the White Paper of the International Network for Sensor Inter-comparison and Uncertainty Assessment for Ocean Color Radiometry (INSITU-OCR) initiative. INSITU-OCR has been created under the framework of the Committee on Earth Observation Satellites (CEOS) Ocean Colour Radiometry-Virtual Constellation (OCR-VC). OCR-VC aims to “provide long time series of calibrated ocean colour radiance at key wavelength bands from measurements obtained from multiple satellites” and its activities include calibration. Successively, the INSITU-OCR white paper recognizes the need for the Space Agencies to facilitate collaboration among sensor characterization and calibration experts with particular expertise in ocean colour instruments for the goal of maximizing the accuracy and temporal and spatial stability of OCR records from individual missions. OCR necessitates special sensor calibration considerations because ocean colour mission requirements are particularly demanding: 0.5% uncertainty in sensor measured Top-of-the-Atmosphere (TOA) radiances as well as a significantly lower uncertainty on sensor characterization and relative radiometric calibration, spatial and temporal (IOCCG, 2012; IOCCG, 2013). A global group of ocean colour instrument calibration experts is small and these challenging requirements are most effectively addressed by their collective effort and sharing of multi-mission experience.
The establishment of the sensor calibration Task Force answers to the needs of all ocean colour missions because accurately calibrated and characterized satellite sensors are a prerequisite for most of the OCR applications, from climate, Earth system science and marine ecosystem monitoring, to operational services including water quality, fisheries and algal blooms. The total 0.5% uncertainty goal dictates that each individual component contributing to this uncertainty has to be characterized to the order of 0.2% or less (IOCCG, 2012) in both pre-launch and on-orbit characterizations. Continuous monitoring of on-orbit temporal degradation needs to assure time-series stability. Although post-launch vicarious calibration removes a global bias from the measurements, any uncorrected instrument effects impact TOA radiance quality, vicarious gain stability, and reduce the accuracy of ocean-colour products.
The ocean-colour needs impose specific mission and instrument requirements as well as calibration and characterization processes which are largely shared among different ocean colour missions. However, the knowledge of those is largely confined to a small group of experts worldwide. This proposal recommends the establishment of the Task Force to unite this expertise and to facilitate cross-pollination, further development and inter-Agency support. The Task Force is proposed to be composed of Space Agency calibration and characterization experts. The experts will meet and interact on specific technical problems, will work hands-on with data, prototype, deliver solutions and transfer the solutions to operations.
Terms of Reference
The Task Force provides a framework under which the ocean colour instrument calibration experts meet and exchange ideas, information and data, as well as conduct hands-on research and implementation. The exchanges as well as the resources are sanctioned by the Agencies contributing to the OCR-VC initiative. The scope of the Task Force responsibilities includes ocean colour satellite sensor calibration and characterization, pre-launch and on-orbit. System vicarious calibration is not in the scope of this Task Force.
The Task Force is a joint IOCCG and CEOS OCR-VC activity in response to the INSITU-OCR White Paper. The Task Force is recognized by CEOS WGCV IVOS, with direct linkages and adoption of IVOS guidelines relevant to ocean colour.
The Task Force reports to IOCCG and CEOS OCR-VC, i.e. INSITU-OCR project office, as well as to CEOS WGCV IVOS. Findings and recommendations are also communicated back to individual Agencies and their groups associated with ocean colour mission performance and cal/val.
The aim of the Task Force is thus not to meet and write a report but to create a permanent inter-Agency platform for joint space instrument calibration and characterization work that is specifically focused on issues related to ocean colour sensors.
The Task Force performs the following functions:
- Definition and prioritization of on-going instrument calibration and characterization issues impacting single and multiple missions.
- Addressing the issues collectively in joint meetings, in focused sub-group working sessions and via active remote collaboration.
- Implementation and validation of the proposed solutions, seeking feedback from the ocean colour community and the Agencies.
- Acting as a centre of continuously advancing expert knowledge on ocean colour instrument calibration and characterization; pre-launch and on-orbit.
- Maintenance of a continuously updated “living” documentation repository (starting with the existing IOCCG reports, e.g. reports 13 and 14).
- Rapid reaction to emerging sensor calibration and characterization issues.
- Further development of sensor calibration and characterization methodologies.
- Validation of proposed calibration and characterization changes and further development of validation methodologies.
- Periodical re-evaluation of ocean colour sensor requirements and provision of guidance for mission requirement definitions.
- Maintenance of an on-line calibration hub, a website or a wiki, for the Task Force member exchanges that is free and open for the ocean colour community (e.g., within the CEOS CalVal portal).
- Provision of an annual report on the status of the Task Force activities, including major achievements, papers in the peer-reviewed literature, conference presentations, assessment reports, and white papers.
The goal of the Satellite Sensor Calibration Task Force is to create a framework for active and hands-on collaboration among instrument calibration and characterization experts from Agencies engaged in the OCR-VC initiative. The collaboration focuses on calibration needs specific to ocean-colour measurements and has the objective to maximize the accuracy and temporal and spatial stability of OCR records from individual missions for the purpose of climate, research and operational applications.
The chairmanship of the Task Force shall be initially established by the inter-Agency executive committee and will be expected to last for a 3-year term. Future rotations of the Chair shall be decided by the Task Force members. The Task Force members will be proposed by the Agencies in agreement with the Chair, initially 1 or 2 members per Agency. The members shall represent expertise in a broad range of satellite ocean colour instrument designs and have hands-on calibration and characterization competences. The membership of the group will not be time limited and the tenure will depend on the member’s availability, the patron Agency, and the Chair. Member rotation or a new member can be proposed at any time. Additional outside experts may be consulted and invited to attend meetings and provide support. The following are suggested membership criteria:
- Hands-on expertise and experience in ocean-colour instrument design, characterization, calibration, and calibration validation; pre-launch and on-orbit.
- Balance between scientific and operational knowledge and experience.
- Good representation of expertise for different instrument types and from individual Agencies.
- Commitment to participate actively in the Task Force.
- Sustenance of comprehensive expertise within the Task Force.
Functioning of the IOCCG Task Force
- The Satellite Sensor Calibration Task Force is envisaged as a long term structure.
- The Task Force is embedded in the extended ocean colour community and closely interacts with it. This interaction is required to gain the community’s feedback and recommendations regarding the accuracy and quality of calibration and characterization of individual instruments.
- The Task Force organizes dedicated sessions during the International Ocean Color Science meetings.
- Beyond the IOCS meetings, the complete Task Force meets in person as often as required, possibly during other scheduled meetings.
- Focused hands-on sub-group working sessions to investigate, implement and validate specific sensor calibration and characterization issues are also supported (potential support including visiting scientist and study programs).
- The Task Force members conduct interim investigative and implementation work at their home Agencies and they stay in continuous contact via mail and the calibration website or wiki.
- The need for the Task Force and the relevance of its Terms of Reference is reviewed and modified as appropriate by the Agencies two years after the establishment of the group, and every three years following the initial evaluation.
- The Chair is given the opportunity to propose new Terms of Reference.
- IOCCG Report Number 13 (2012): Mission Requirements for Future Ocean-Colour Sensors, Edited by: Charles McClain and Gerhard Meister
- IOCCG Report Number 14 (2013): In-flight Calibration of Satellite Ocean-Colour Sensors, Edited by: Robert Frouin