Vicarious Calibration of the TUBIN Infrared Sensor Suite.

TUBIN is a microsatellite mission tasked with the detection of high-temperature events from low-Earth orbit. Launched in June 2021, it employs a sensor suite consisting of two microbolometer focal plane arrays sensitive in the thermal infrared range of the electromagnetic spectrum as well as a complementary camera sensitive in the visible range. Thermal anomalies are detected within readings of the infrared sensors and their localization is assisted by the visible camera. The microbolometer sensors were calibrated on-ground. However, to account for limitations within the ground calibration setup and sensor degradation and alterations within its nominal lifetime, the sensor response shall be validated in orbit. In absence of a radiometric calibration source aboard the satellite, uniform and well-documented radiometric sources were evaluated for in-orbit calibration. Advantages and disadvantages of different sites are discussed in this paper and the agreement between ground and in-orbit calibration results are outlined.