A visibility measurement system that computes relative visibility by comparing
an images of an environment against a benchmark image. A sensing device receives
an image and a digital conversion system maps the image into a two-dimensional
data array. A processor converts the digital data to a value that represents visibility
by identifying a region in the image that has a uniform distance from the sensing
device over time, computing a benchmark visibility index for the region as a summation
of measurable visual characteristics that influence visibility in the region under
a benchmark environmental condition, computing a second visibility index for a
second environmental condition, and computing a relative visibility value as the
ration of the second visibility index in relation to the benchmark visibility index.