Restoring the aerosol optical depth by ground measurements of SPM photometer

Measurements of the aerosol optical depth (AOD) in the Lower Volga region by using photometer SPM, developed at the Institute of Atmospheric Optics, were made. This photometer detected and recorded the signals coming from the sun in a cloudless sky $10$ spectral channels $0.339$, $0.373$, $0.439$, $0.499$, $0.673$, $0.871$, $0.939$, $0.1044$, $0.1555$ и $0.2139$ $\mu {\rm m}$. The technique for retrieval of AOD from signals photometer was described in this article. Measurement results of SPM photometer and CE 318 photometer of AERONET network were compared. SPM photometer was tested for the presence of errors in each of the measurement channels, which are mainly due to operator error when pointing at the sun. Practically in all spectral channels (except $0.499$ $\mu {\rm m}$) AOD standard deviations were smaller value $0.01$, when averaged over $30$ minute intervals. Comparison of the distribution functions of the aerosol particle size of the retrieval from different photometers measurements of AOD was performed. There was quite a typical situation: the distribution function for the fine fraction recovered from the data for different photometers, found themselves close enough, while for coarse fraction has been some discrepancy. We believe that the reason for this is the large measurement error of AOD of SPM photometer compared to 318 CE photometer.