Progress Towards Massively Parallel Smartphone Sunphotometry

Sun photometers are devices that use the sun as a light source to measure the transmission of the atmosphere. The resulting data can be used to determine the optical thickness due to aerosols or the concentration of light absorbing gases. Smart phones equipped with cameras are becoming increasingly prevalent, and are potentially useful for scientific research. Smart phones contain integrated sensors to measure light intensity and location, and this capability is coupled with unmatched ability to quickly communicate sampled data to a central location for processing. One can quickly imagine the possibility of a massively parallel network of smartphone sensors tracking evolving atmospheric conditions such as aerosols, water vapor, UV index, or ozone. In this work, we will present initial data characterizing a smart phone sun photometer. An iPhone was combined with different bandpass filters to spectrally select wavelength bands of interest. Test filters of known transmittance were then placed in the beam path and the iPhone was used to assess percent transmittance. By comparing the iPhone measured value with accepted values, the accuracy of the smartphone device can be constrained to roughly ± 5–10%. In addition, surface solar intensity changes have been monitored as a function of time of day (airmass effect) or during periods of different aerosol loadings. Taken together, results suggest smartphone sun photometers may not offer exceptional accuracy and precision compared to commercial devices, but the prospect for massively parallel measurements has significant potential for gaining knowledge in atmospheric chemistry