This sensor's purpose is to detect if we have entered a cloud. The cloud types we may encounter are water droplets like fog, and more likely ice crystals. The sensor should be able to detect both. The sensor could be a binary 1/0 output, or a relative measurement. It should not be negatively affected by the outside temperatures of the mission, and should not place sensors behind any kind of window. (Windows create frost/condensation risk) It should not be affected by direct sunlight or darkness. It should be lightweight and low power. Momentary measurement would be preferred to long powered on operation.
Sensor will be mounted so the the opening is facing vertically, extending out as far to the side as possible, to avoid being shielded from falling snow by the balloon envelope. Possibly on a short boom.
Cirrus cloud ice particles seem to be likely to be between 1μm and 10μm in diameter, according to a study of tropical cirrus clouds1). Another study cites however that they may range from 1μm to 750μ(Paper: Microphysical and Optical Properties of Cirrus and Contrails)). This should be well within the detection range for the Sparkfun Dust sensor.
This is an analog sensor, it is susceptible to powerline noise. Make sure the power is well-filtered, and test it with the other systems running. Read this only when sat modem is NOT transmitting.