A Preliminary Study on the Possibility of Estimating Total Atmospheric Ozone from Satellite Measurements

Abstract

This paper is concerned with a preliminary study of the feasibility of determining total atmospheric ozone from satellite measurements of the solar ultraviolet radiation diffusely reflected by the earth's atmosphere. The atmospheric model used is plane-stratified, and the evaluation of the radiation field takes into account all orders of Rayleigh scattering. In addition, the model provides for variations in the total amount and vertical distribution of ozone, as well as the Lambert reflectivity and pressure at the effective base of the atmosphere. The results indicate that the wavelength region in which measurements should be made lies between about 3125 and 3175 Å, if the observations are restricted to the nadir direction. Wavelengths shorter than 3125 Å do not penetrate adequately through the ozone layer and do not, therefore, contain information on total ozone content. On the other hand, wavelengths much longer than 3175 Å although they penetrate the ozone layer, in general offer rather poor sensitivity to total ozone. The accuracy of total ozone determinations, based on measurements at a single wavelength, is not likely to be better than 10% even if the intensity ratio (diffusely reflected to extraterrestrial input flux) is measured within 1%, reflectivity within 0.05, and cloud-top or surface pressure within 50 mb. More accurate determinations of surface reflectivity are essential for improving the accuracy of the total ozone determination. Measurements on a pair of wavelengths, one within the 3125?3175 Å range and the second at 3300 Å, are found to reduce the effects of reflectivity. Over a moderate range of solar zenith angle, measurements on the wavelength pair (3175, 3300,Å) will permit deduction of total ozone within 5%, provided the various quantities are determined with the above-noted accuracies. When the zenith angle of the sun exceeds about 60°, penetration of the ozone layer is incomplete and a simultaneous determination of the high level ozone distribution from measurements at still shorter wavelengths is necessary for optimum accuracy of the total ozone determination.