A Method for Inferring Total Ozone Content from the Spectral Variation of Total Optical Depth Obtained with a Solar Radiometer

Abstract

A solar radiometer has been used to monitor solar irradiance at eight discrete wavelengths. From these monochromatic measurements at varying zenith angles the total optical depth has been deduced by a computerized curve-fitting method. A unique technique will be described whereby the ozone absorption optical depths, and hence total ozone content of the atmosphere, can be inferred directly from the spectral variation of total optical depth. This procedure permits a systematic determination of total ozone content on a daily basis when other measurements are not available. Using the ozone absorption optical depths determined in this manner, the values of aerosol optical depth may be obtained more accurately by subtracting the molecular scattering and estimated ozone absorption contributions from the total optical depth. A technique is also described for estimating the absorption optical depths at wavelengths where additional molecular absorption other than ozone occurs. Results are presented as 1) daily values of total ozone content and 2) molecular absorption optical depths due to water vapor and oxygen at two of the radiometer wavelengths. The total ozone content exhibits the characteristic seasonal cycle with peak values in April.