Abstract: A plurality of image pickup devices are set on the ground to pick up images of an anti-collision light located on an aircraft to be guided. A position reference producing section produces a signal representing a position reference of the aircraft in accordance with picked-up image signals from the plurality of image pickup devices. A display data producing section produces at least one of direction information and distance information as guidance information to be provided to pilots of the aircraft in accordance with the signal representing the position reference of the aircraft which is supplied from the position reference producing section. A display unit displays at least one of the direction information and distance information from the display data producing section at a position on the ground where the pilots can see and recognize the information.

Abstract: A water film surface is irradiated with light from a detecting unit's light source. Light reflected from the water film surface is converted into an electrical signal by a sensor (photoelectric converting means) in the unit. The converted electrical signal is supplied to a processing unit through a cable. The processing unit calculates the water film thickness based on the electrical signal. The calculated thickness is displayed on a display in the detecting unit.