Calibration parameters

The Ground Data Processing Software (GDPS) processes raw OMI instrument level-0 data into geophysically calibrated level-1b data. The GDPS uses a so-called Operational Parameters File (OPF), that contains all instrument calibration and characterisation parameters required for level-0 to 1b data processing.

The goal of the in-flight calibration is to maintain the accuracy of the OPF in flight. The following parameters are investigated / monitored:

Optics calibration parameters

• Absolute Earth radiance calibration
• Absolute irradiance calibration
• Absolute Earth reflectance calibration
• Irradiance goniometry (azimuth and elevation angle dependence)
• Characterisation of spectral and spatial diffuser features
• Spectral calibration, including optical bench temperature dependence
• Spectral slit function calibration
• Spectral stray light calibration, including spectral stray light warning flagging
• Spatial stray light calibration using the lower and upper stray light areas on the CCD detectors
• Geolocation calibration, viewing properties
• Signal-to-noise
• Spectrometer entrance slit irregularity
• Potential optical degradation of the Earth radiance optical path
• Potential optical degradation of the sun irradiance optical path
• Potential optical degradation of the internal White Light Source (WLS) optical path
• Polarisation sensitivity (only on the ground)

Detector calibration parameters

• Pixel-to-pixel non-uniformity (PRNU) calibration
• Dark current / background calibration, including detector temperature dependence
• Random Telegraph Signal (RTS) effects
• Bad and dead pixels calibration
• Charge Transfer Efficiency (CTE) / Charge Transfer Inefficiency (CTI) effects
• Transient signals resulting from impact of high-energetic protons on the detectors, including flagging

Electronics calibration parameters

• Non-linearity calibration, including non-linearity warning flagging
• Offset calibration
• Gain ratio calibration
• Detector Module (DEM) saturation flagging