Authors describe details of the processor used in MethaneAIR, which converts raw (Level 0) sensor data into calibrated, geolocated, and scientifically usable radiance data (Level 1B) through dark current correction, noise estimate, stray-light removal, spectral calibration, radiometric correction, and orthorectification. It sets the foundation for operational MethaneSAT Level 0 to Level 1B processor.