Slant Range Visibility Measurement for Aircraft Landing Operations

A method of determining slant visibility by lidar observations from the ground during various degrees of fog and low cloud conditions was investigated in an experimental program at a coastal site. The emphasis of the study was on the operational aspects of landing aircraft in Categories I and II conditions, and the first concern was to ascertain whether a pilot might be expected to obtain visual reference from the critical heights of 200 ft and 100 ft respectively. This depends primarily upon the transmittance along the slant path from the cockpit to the ground. The air of the lidar observations was to determine the conditions of atmospheric transmittance aloft, with special reference to whether the appropriate minimum values are exceeded.