Direct and Indirect Comparisons to Support Ongoing Validation of the Sentinel-3 Active Fire Products

Continuous evaluation and ongoing validation the accuracy of active fire products derived from spaceborne instruments is of prime importance for ensuring continuity of measurements, as well as the quality of the resulting science. In this work, we present methods that are currently being setup to continuously evaluate the active fire products obtained by the SLSTR instruments aboard Sentinel-3A and Sentinel-3B, both by direct comparisons with MODIS Terra measurements, and indirect comparisons between S3A and S3B. We show that there is currently a good agreement between MODIS and SLSTR Fire Radiative Power (FRP) data, as well as between the FRP detected by S3A and S3B. We propose an indirect method to detect instrument anomalies in the absence of a "reference" sensor for simultaneous nadir acquisitions, building on the fact that S3A and S3B have the same SLSTR instrument specifications and the same local time at descending node. These results indicate that Sentinel-3 SLSTR can ensure the continuity of remote sensing observations of fire activity after the demise of MODIS.