Research on a Partial Aperture Factor Measurement Method for the AGRI Onboard Calibration Assembly

Area of Science:

• Remote Sensing
• Optical Sensor Calibration
• Radiometry

Background:

• Large aperture optical remote sensors present unique onboard calibration challenges.
• Accurate calibration is vital for reliable Earth observation data.
• The FengYun-4 (FY-4) advanced geostationary radiance imager (AGRI) requires precise calibration.

Purpose of the Study:

• To develop and validate a partial aperture onboard calibration method for the AGRI.
• To accurately measure the partial aperture factor (PAF) for AGRI bands B1-B3.
• To analyze the uncertainty associated with the PAF measurement.

Main Methods:

• Utilized the solar diffuser reflectance degradation monitor (SDRDM) as a reference radiometer.
• Established a linear response relationship between AGRI and SDRDM under a common radiance source.
• Calculated relative reflectance ratio using the solar diffuser's bidirectional reflection distribution function (BRDF).
• Simulated onboard calibration measurements in a laboratory setting using a solar simulator.

Main Results:

• Achieved high-precision measurement of the partial aperture factor (PAF) for AGRI bands B1-B3.
• Determined the measurement uncertainty of the PAF to be greater than 2.04%.
• Validated the effectiveness of the partial aperture calibration approach.

Conclusions:

• The developed partial aperture onboard calibration method is effective for large aperture remote sensors like AGRI.
• The measured PAF provides a critical reference for evaluating post-launch absolute radiometric calibration uncertainty.
• This method is significant for the advancement of optical remote sensor calibration.