Outcome of Workshop on SI-Traceable Space-based Climate Observing System (SITSCOS)
by Prof. Nigel Fox, Dr. Tim Hewison, Dr. Greg Kopp, Dr. Bruce Wielicki

Abstract

The SI-Traceable Space-based Climate Observing System Workshop (SITSCOS) was hosted by the National Physical Laboratory, UK (2019) and sponsored by the UK Space Agency. The workshop was organized under the auspices of the Global Space-based Inter-Calibration System (GSICS) and the Committee on Earth Observation Satellites - Working Group on Calibration and Validation (CEOS-WGCV). The international workshop included about 100 attendees including users, satellite instrument designer/builders, metrologists, and space agencies with expertise across a wide range of applications and technologies. This paper introduces the Workshop Report, which integrates information from the last decade of progress on laboratory metrology, SI-traceability of satellite instruments, GSICS inter-calibration, CEOS Cal/Val activities, climate science uncertainty requirements, and analysis of the economic value of more accurate climate change observations. The report addresses not only climate observations but also the advantages of improved SI-traceability for other space-based applications such as weather prediction/analysis/re-analysis, land & ocean surface imaging, microwave imaging/sounding. The Workshop Report summarizes the results of the workshop in a form that can be easily understood and used by the research community as well as space agency program managers and other related organizations. It includes a Summary Report, authored by the workshop’s Science Organizing Committee, which provides a high-level overview of the workshop and its conclusions as a concise, standalone document. The remainder of the report is broken into several sections for easy access, organized by application, remote sensing spectral region, and type of measurement. The Workshop Report is available along with the presentations at https://calvalportal.ceos.org/sitscos-ws and is complemented by a special issue of the journal Remote Sensing. The report includes a summary of published climate observing system accuracy requirements and compares current capabilities to them, finding that current climate observation uncertainty is typically 2 to 10 times greater than that required to both survive observation gaps as well as to verify in-orbit calibration drifts over time. The workshop concluded that advances in ground-based calibration metrology as well as new approaches to fly reference spectrometers in orbit offer the ability to bridge the gap between current and needed capabilities in the near future. Furthermore, reference SI-Traceable Satellite (SITSat) spectrometers capable of in-orbit calibration transfer through inter-calibration were recommended by the workshop as the least expensive and most robust means to achieve climate change calibration capability in orbit. The first of these SITSats are planned for launch this decade, including NASA’s CLARREO Pathfinder, ESA’s TRUTHS and FORUM, and the Chinese Space Agency’s LIBRA.