DETERMINATION OF ATMOSPHERIC TURBIDITY FROM THE DIFFUSE-BEAM BROAD-BAND IRRADIANCE RATIO

A semi-physical method is proposed to evaluate turbidity from broadban d irradiance measurements and other atmospheric parameters. This metho d demonstrates the utility of diffuse data when estimating atmospheric composition with broadband irradiance data. An error analysis and var ious tests against measured data show that this method can predict acc urate turbidities provided that the sky is perfectly cloudless and the diffuse irradiance data are very accurate. Yet, this method is insens itive to errors in input data such as precipitable water and ozone amo unt. Applications of this method to the quality control of radiation d ata are discussed. Tests with actual data from Florida and Oregon show good agreement with other methods. Evaluation of the model required a detailed discussion of the accuracy and cosine error of pyranometers, and the uncertainty in precipitable water estimates. (C) 1998 Elsevie r Science Ltd. All rights reserved.