The calibration of Microtops II sun photometers over ocean

Abstract

Aerosol plays important on the climate and environment. Aerosol parameter, such as optical thickness, is usually measured by the 5-channel hand-held MICROTOPS II sun photometer and the calibration coefficients of instruments measurements play a vital role in determining the accuracy of the aerosol optical thickness. However, long time usage and some clean operation of the MICROTOPS II sun photometer maybe make the sensitivity decline or lead some system excursion. It needs to update calibration constants annually to obtain some precise aerosol optical thickness. It is fussy that the general method use Langley-plot technique in clear and stable atmosphere condition or standard lamp in laboratory. According to marine atmosphere status and measurement conditions, the measurement under relative stable atmosphere condition on Dec 6, 7 2008 is selected as calibration experiment. By analyzing the aerosol optical thickness measured by the instrument with factory calibration constants, it is certain that the variety of atmosphere is stable or the variety of atmosphere optical thickness is slowly linear decreasing or increasing by the reorganization of measurements. The three continuous measurements are set as a group. Using similar Langley plot method with those groups, a new method to calibrating the 5-channel MICROTOPS II sun photometer which is named as SIO maritime measurement calibration method is presented. The calibration coefficients at five wavelengths is obtained by the new method and compared with the factory calibration and Langley plot method. It shows that the proposed calibration way can be conduct handily in the common atmospheric environment and maritime observation. It can provide good aerosol optical thickness at each measurement using this way.