Visibility Monitoring using Mobile Phones

Airborne particulate matter is a serious threat to both our health and the environment. It is also the primary cause for visibility degradation in urban metropolitan areas. We present the design, implementation, and evaluation of an optical technique to measure visibility using commodity cameras and other sensors commonly found on mobile phones. The user takes a picture of the sky which is tagged with location, orientation, and time data and transfered to a backend server. Visibility is estimated by first calibrating the image radiometrically and then comparing the intensity with a physics-based model of sky luminance. We describe the challenges for development of the system on the HTC G1 phone running the Android OS. We study the sensitivity of the technique to error in the accelerometers and magnetometers. Results from images gathered in Phoenix, Arizona and the Los Angeles basin compare favorably to air quality data published by the US Environmental Protection Agency.