We should talk on Monday morning!!! What on earth are they trying to do now? Presumably its for the EVS?
I think the device you are looking for is a transmissometer. It measures the amount of light that is refracted by water or particulates and, if you have a calibration, you can thence estimate denisty of the particulate etc.
By definition - fog is low lying so why would we need something on the air vehichle? To measure the benefit of peering through it I assume?
Would it not be sufficient to use the RVR measuring systems on the field? maybe it would be worth talking the folks that run the NOAA station on Tyler just south of our happy place of work!