Modeling Infrared Radiometer Self-Emission With Application to MetOp/HIRS

This paper presents a generic self-emission model for infrared (IR) radiometers where the relationship between the instrument self-emission and calibration intercept is analyzed. This model is applied to both the prelaunch and on-orbit MetOp/High-Resolution IR Radiation Sounder (HIRS) calibration data. For MetOp/HIRS, the changes in intercept due to self-emission variations between calibration events are up to 1% of the onboard blackbody calibration radiance. The impact is dependent on Earth scene brightness temperature and channel wavelength. The investigation shows that the intercept variation due to self-emission is significant and, if not corrected, can induce errors of up to 1 K for Earth scenes with 285 K brightness temperature and higher for Earth scenes with lower brightness temperatures. Based on this self-emission model, an improved in-flight calibration algorithm is proposed to reduce systematic calibration errors. We believe that this model can improve accuracy and consistency of level 1b radiance for climate studies and can be applied to other IR radiometers.