A lunar radiometer for night-time optical depth measurements

A lunar radiometer was developed and used for the measurement of night-time aerosol optical depth. Analogous to its counterpart, the solar radiometer, the lunar radiometer measures the direct lunar irradiance at the desired wavelength as a function of lunar zenith angle. From this the night-time aerosol optical depth is evaluated and compared with the daytime aerosol depth values obtained using a solar radiometer. The results indicate a significant enhancement in aerosol optical depth during the night especially in winter months, which is mainly attributed to the day-night changes in relative humidity