Calculation algorithm for spectral irradiance using broad-band optical filter data

Abstract A disposable miniature radiometer has been developed using optical filters for spectral separation. Limitations in accurately retrieving irradiance from the broad-band measurement results can be attributed to the broad-band filters. This paper proposes an algorithm for spectral irradiance using broad-band optical filter data (SIBOF algorithm) to achieve precise retrieved irradiance through four correction steps. First, the algorithm uses an energy ratio method to adjust the broad-band data to narrow-band data. The energy ratio is derived from the reference lamp spectrum and measured optical filter transmissivities. Second, the algorithm corrects for filter transmissivity differences by multiplying the normalized spectral transmissivities by calibration coefficients. The third step involves polarization correction, compensating for additional transmissivity caused by polarization effects from the film overlying on the cosine collector, thus eliminating errors due to film polarization. The fourth step involves radiative heating correction, where fitting curves and coefficients are used to analyze the relationship between irradiance deviation and actual irradiance to correct the data. Standardized tests indicate that, after applying the four corrections, the results are highly consistent with the irradiance from the reference radiometer, demonstrating that these correction steps constitute a reliable algorithm for spectral irradiance using broad-band optical filter data. In April 2024, a 20-day sea fog sounding observation was conducted at the Qianliyan Ocean Station. The irradiance data from the miniature radiometers before launch were corrected and compared with those measured by the reference radiometer on the ground. Results indicate that the irradiance retrieved through the algorithm was in good agreement with the measurements from the reference radiometer, validating its performance across various weather conditions.