Temperature correction method and verification of the CW193 sun–sky photometer

The performance of the CW193 photometer in the 1020 and 1640 nm infrared channels is highly temperature-dependent owing to the influence of the detector material. To eliminate the temperature dependency of the CW193 photometer in the infrared channels, and to improve aerosol optical depth (AOD) inversion accuracy, we obtained observational data using the CW193 photometer at the Beijing-CAMS site of the Aerosol Robotic Network (AERONET), together with reference observational data obtained concurrently using a CE318-T photometer at the same site. Comparison and validation with AERONET data revealed correlation coefficients of 0.978 and 0.991 and root mean square errors (RMSEs) of 0.027 and 0.011 for 1020 and 1640 nm channel irradiance, respectively. The correlations between the irradiance ratio and temperature in the 1020 and 1640 nm channels of the CW193 photometer and the reference photometer were analyzed using both linear and exponential models to derive temperature correction coefficients for these channels. The derived temperature correction coefficients were employed in calibrating digital number values for the 1020 and 1640 nm channels of the CW193 photometer to eliminate the impact of temperature. Irradiance in the 1020 and 1640 nm channels of the CW193 photometer obtained after temperature correction, validated against the corresponding AERONET reference data, revealed that the correlation coefficients were all 1, and that the RMSEs were 0.005 and 0.001, respectively. These results indicate that observation datasets obtained using the infrared channels of the CW193 photometer after temperature correction have excellent agreement with the AERONET observation datasets. Consequently, the process of temperature correction effectively eliminates the impact of temperature and enhances the accuracy of AOD inversion in the infrared channels of the CW193 photometer.