Method to intercalibrate sunphotometer constants using an integrating sphere as a light source in the laboratory

Area of Science:

• Atmospheric Science
• Optical Remote Sensing
• Metrology

Background:

• Sunphotometers are crucial for atmospheric observation, requiring accurate calibration.
• Traditional calibration relies on sunlight at specific sites, facing limitations like weather dependency and logistical challenges.

Purpose of the Study:

• To introduce and validate a novel laboratory-based calibration method for sunphotometers.
• To enable reliable transfer of calibration constants using an integrating sphere, accounting for optical properties.
• To establish a standardized, weather-independent calibration approach for global aerosol monitoring networks.

Main Methods:

• Utilized a laboratory integrating sphere as a stable light source for calibration constant transfer.
• Incorporated viewing solid angle and spectral response effects into the calibration transfer process.
• Experimentally validated the method on four CIMEL CE318 sunphotometers within the AERONET network.

Main Results:

• The laboratory calibration method demonstrated an average difference of 1.4% compared to AERONET operational calibration results.
• Error analysis confirmed that the method's uncertainty is consistent with estimations and offers potential for further improvement.
• The approach successfully accounts for key photometer optical characteristics during calibration transfer.

Conclusions:

• The developed laboratory calibration method provides a reliable, weather-independent alternative to traditional sunphotometer calibration.
• This method enhances data continuity by reducing interruptions from operational calibration requirements.
• It lays the foundation for a unified global aerosol measurement network utilizing diverse sunphotometer types calibrated against a single standard.