There are two different kinds of wind detectors aboard Pathfinder, using two different technologies. The differential cooling and heating effects of wind blowing over these detectors, as well as variations from side to side, were transformed into measurements of speed and direction. There were initially some problems with the exact calibration of the wind sensors, so the experimenters began reporting results in relative terms such as light, strong, etc., rather than absolutes. However, they now feel comfortable with interpreting the varying positions of the wind socks as indicating speeds around 12 kms per hour, very much in line with the results obtained from the wire sensors atop the met mast. Viking had only one set of wind sensors, so again, Pathfinder's instrument package is a significant advance.
Wind is a very important force in shaping the Martian surface.
These results were used to help determine the age of features around the landing site by analyzing how much dust has built up. It may seem strange to list the camera as a weather instrument, but it returned at least four sets of very interesting meteorological data. First, it showed much more detail about morning and evening clouds than did the Viking cameras. The dramatic sunset images are impressive, but to scientists the high, early morning wispiness is just as fascinating. They think they may be seeing carbon dioxide clouds, formed overnight when temperatures plummet and dispersing as the atmosphere warms up.