The WGCV undertakes a variety of activities related to the calibration and validation (cal/val) of Earth Observation data. Our current activities focus mainly on the requirements identified by the intergovernmental Group on Earth Observations (GEO) and their goal to achieve a Global Earth Observation System of Systems (GEOSS). To this end, GEO has identified a series of tasks related to calibration and validation in which we play a lead role. Some of our current activities include:
ACIX/CMIX – Atmospheric Correction and Cloud Mask Intercomparison Exercises
NASA and ESA have collaborated within the framework of CEOS to conduct three workshops thus far on the intercomparison of Atmospheric Correction and Cloud Mask algorithms. The impetus for such an effort has been the evolution of multiple high-resolution sensors that have facilitated the analysis of long time-series. The essential step of creating consistent surface reflectance (SR) products from these sensors was begun by mulitple entities, for SR products from sensors such as Landsat-8 and Sentinel-2. This intercomparison of atmospheric correction processors began in early 2016, and thier aim to point out strengths and weaknesses as well as commonalities and discrepancies of the various processors being implemented.
Many teams with atmospheric correction algorithms were invited to pariticipate, and 12 teams partook in the first exercise, ACIX I. Currently, a total of 35 teams are participating from US, Europe, Australia and China. In the second exercise, ACIX II, the atmospheric correction is divided into two parts, one over land, and the other over water. And, in parallel, a Cloud Mask intercomparison exercise is also implemented.
The current status of these activities, following the first ACIX II/CMIX workshops is:
- Agreement to include surface reflectance measurements from RadCalNet (LaCrau and Gobabeb), campaign data from DLR and surface reflectance measurements from GeoSciences Australia.
- Consensus by all the teams on the need for automated surface reflectances over vegetated/low-reflectance targets.
- The test sites of ACIX II-Land will be all the AERONET sites with currently available measurements (≈150 sites identified).
- For ACIX II-Water, the sites will be confirmed depending on the availability of in situ data, which are currently being collected by the coordinators.
- For CMIX, the sites/scenes will be selected based on the various available validation datasets.
- There are anticipated issues with the download and processing of large volumes of data involved in the comparison. Multiple alternatives are being considered.
- The follow-on workshop will be take place at ESRIN in mid to late 2019.
Radiometric Calibration Network Web Site Operational
Following years of planning, development, and beta testing, we are pleased to announce the release of the RadCalNet web portal to the public!
RadCalNet provides satellite operators with SI-traceable Top-of-Atmosphere (TOA) spectrally-resolved reflectances to aid in the post-launch radiometric calibration and validation of optical sensors onboard Earth Observation satellites.
The initial set of instrumented reference test sites are:
- Railroad Valley Playa, USA, operated by the University of Arizona
- La Crau, France, operated by CNES
- Baotou, China, operated by the Chinese Academy of Opto-electronics (AoE)
- Gobabeb, Namibia, operated by ESA/CNES
Each member site takes responsibility for the quality assurance of the surface/atmosphere measurements provided and is subject to peer review and rigorous comparison to ensure site-to-site consistency and SI traceability. The archive is continuously updated, and new sites that meet RadCalNet requirements may be added.
Land Product Validation Subgroup Protocols
One of the primary objectives of WGCV’s Land Product Validation (LPV) subgroup is the development of best practice protocols for Essential Climate and Biodiversity Variables (ECVs and EBVs). The LPV subgroup has published two such protocols, and have two more currently under development. The LPV focus areas on LAI and LST have published protocols that can be found in the Documents section of the LPV website.
LPV’s Surface Radiation focus area has a final draft of the Albedo Best Practice Protocol currently under review, and they hope to be ready for publication by the end of 2019.
The LPV Biomass focus area is currently developing the same for Biomass products, and they have enlisted a large, multi-institutional group of contributors for this effort. In addition to this large development group, the Biomass focus area leads are engaging with the ESA Biomass and NASA GEDI missions, CCI Biomass, GFOI, and the CEOS Working Group on Climate, to be inclusive of all stakeholders.