A system for measuring a parameter of a medium with a vehicle moving in a traveling direction through the medium includes four detecting portions and a calculating portion. The four detecting portions respectively detect first through fourth values of the parameter from first through fourth lines-of-sight in first through fourth directions at first through fourth positions of the vehicle at first through fourth times. The first line-of-sight and the third line-of-sight are in a first plane and intersect at a first intersection, while the second line-of-sight and the fourth line-of-sight are in a second plane and intersect at a second intersection. The calculating portion calculates the parameter based on the first through fourth values and the first and second intersections.