Four radiometric models are compared to study the Angstr?m turbidity coefficient over Gharda?a (Algeria). Five years of global irradiance measurements and space data recorded with MODIS are used to estimate . The mode...Four radiometric models are compared to study the Angstr?m turbidity coefficient over Gharda?a (Algeria). Five years of global irradiance measurements and space data recorded with MODIS are used to estimate . The models are referenced as for Dogniaux’s method, for Louche’s method, for Pinazo’s method, for Gueymard’s method and by for MODIS data. The results showed that and are very close as the couple and . values are between them. Results showed also that all Angstr?m coefficient curves have the same annual trend with maximum and minimum values respectively in summer and winter months. Annual mean values of increased from 2005 to 2008 with a slight jump in 2007 except for . The city environment explains it since the urban aerosols predominate over all other types during this period. The jump in 2007 is attributed to the ozone layer thickness that undergoes the same behavior. Some models are then more sensitive to this atmospheric component than others. The occurrence frequency distribution showed that , , , and had their maximum recurrent values near 0.03, 0.07, 0.10, 0.09 and 0.02 respectively. The cumulative frequency distribution revealed also that and yielded maximum “clean to clear” conditions with respect to others while and had the minimum. The opposite was observed on the same pairs with regard to “clear to turbid” and “turbid to very turbid” conditions. Louche’s model gave middle values of sky conditions comparing to the other models.展开更多
文摘Four radiometric models are compared to study the Angstr?m turbidity coefficient over Gharda?a (Algeria). Five years of global irradiance measurements and space data recorded with MODIS are used to estimate . The models are referenced as for Dogniaux’s method, for Louche’s method, for Pinazo’s method, for Gueymard’s method and by for MODIS data. The results showed that and are very close as the couple and . values are between them. Results showed also that all Angstr?m coefficient curves have the same annual trend with maximum and minimum values respectively in summer and winter months. Annual mean values of increased from 2005 to 2008 with a slight jump in 2007 except for . The city environment explains it since the urban aerosols predominate over all other types during this period. The jump in 2007 is attributed to the ozone layer thickness that undergoes the same behavior. Some models are then more sensitive to this atmospheric component than others. The occurrence frequency distribution showed that , , , and had their maximum recurrent values near 0.03, 0.07, 0.10, 0.09 and 0.02 respectively. The cumulative frequency distribution revealed also that and yielded maximum “clean to clear” conditions with respect to others while and had the minimum. The opposite was observed on the same pairs with regard to “clear to turbid” and “turbid to very turbid” conditions. Louche’s model gave middle values of sky conditions comparing to the other models.
