The method for two-wavelength calibration of the Sun photometers upon two optical air masses

It is noted that the major method used for calibration of the Sun photometers is still the Langley method. The major weakness of the Langley method is temporal instability of drawn graphical diagrams, caused by instability of optical depth of atmospheric aerosol. The temporal instability of atmospheric aerosols optical depth leads to change in the steepness of drawn up diagrams and, as a result, to random shifts of graphically calculated calibration quantity. Another signicant limitation of the Langley method is the lack of fully analytical formula for calculating calibration quantity and the necessity to draw the graphics. There are some modications of the Langley method, for example, there is an analytical method making it possible to calculate the calibration quantity analytically upon two optical masses, where the instability of basic method remains. It is well known that optical masses of different atmospheric gas components signicantly differ upon low height angle of the Sun. Thus, the measurements carried out in broadband of the Sun elevation angles variation cannot be estimated as variation of common optical mass in the same band. This fact signicantly limits the possibilities of the known method. The article describes the suggested two-wavelength method for calibration of the Sun photometers in two optical air masses. It is shown that transition from the one-wavelength method to the two-wavelength method make it possible to decrease signicantly the aerosol error of calibration method applied upon two air masses. The two-wavelength method for calibration of the Sun photometers upon two optical masses suggested in this article make it possible to remove the impact of atmospheric conditions on results of calibration inherent for the one-wavelength method realized upon two optical masses. The suggested method makes it possible to increase the accuracy of sun-photometric measurements of atmospheric trace gases and aerosol.

sun photometer, calibration, optical air mass, error, aerosol, atmosphere

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