Development of an integrating sphere calibration method for Cimel sunphotometers in China aerosol remote sensing network

Abstract Based on the integrating sphere traced from the National Institute of Standards and Technology (NIST, USA), a sphere calibration method and protocol for the China aerosol remote sensing network (CARSNET) Cimel sun photometer was established. Four CE318 sun photometers were verified using the proposed calibration method and operational protocol. The calibration results showed that the instrument coefficients differed by less than 3% for visible (∼5% for infrared) wavelengths from the original ones stated by Cimel Electronique. In situ validation experiment data showed that radiances at ±6° measured by sun collimator (aureole) were consistent with those measured by sky collimator (sky), under both almucantar (ALMUC) and principal plane (PPLAN) scenarios. Differences at all wavelengths were less than 1%, indicating that the method and protocol are suitable for CARSNET field sun photometer calibration, and would benefit improvement of data quality and accuracy of network observations.