Julia A. Barsi

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1. Introduction The Landsat 9 observatory is the latest satellite in the Landsat mission series. It launched on 27 September 2021. Similar to Landsat 8, Landsat 9 includes two imaging radiometer payloads: the Operational Land Imager (OLI), which is the subject of this paper, and the Thermal Infrared Sensor (TIRS), whose initial transfer to orbit activities are covered elsewhere [1].

The accuracy of the absolute radiometric calibration (RadCal) for remote sensing instruments is essential to their wide range of applications. The uncertainty associated with the traditional source-based RadCal method is assessed at a 2% (${k} = {1}$) or higher level for radiance measurement. To further improve the accuracy to meet the demands of climate studies, a detector-based approach using tunable lasers as a light source has been devised.