2022 CEOS International Thermal Infrared Radiometer Comparison: Part I: Laboratory Comparison of Radiometers and Blackbodies

An international comparison of field deployed radiometers for sea surface skin temperature (SSTskin) retrieval was conducted in June 2022. The campaign comprised a laboratory and a field comparison. In the laboratory part the radiometers were compared against reference standard blackbodies, while the same was done with the blackbodies used for the calibration of the radiometers against a transfer standard radiometer. Reference values were provided by the National Physical Laboratory (NPL), traceable to the primary standard on the International Temperature Scale of 1990. This was followed by the field comparison at a seaside pier on the south coast of England, where the radiometers were compared against each other while viewing the closely adjacent surface of the sea. This paper reports the results of the laboratory comparison of radiometers and blackbodies. For the blackbody comparison, the brightness temperature of the blackbody reported by the participants agreed with the reference value measured by the NPL transfer standard radiometer within the uncertainties for all temperatures and for all blackbodies. For the radiometer comparison, the temperature range of most interest from the SSTskin retrieval point of view is 10 °C to 30 °C, and in this temperature range, and up to the maximum comparison temperature of 50 °C, all participants’ reported results were in agreement with the reference. On the other hand, below 0 °C the reported values showed divergence from the reference and the differences exceeded the uncertainties. The divergence shows there is room for improvement in uncertainty estimation at lower temperatures, although it will have limited implication in the SSTskin retrieval.