On-board measurement system for the automatic determination of small snow thicknesses on airport runways

Management authorities of major airports dread the presence of snow on runways. Snow-thickness information must be communicated to pilots after measurements have been made at differents points of the runway and decisions taken with regard to snow-clerance or closure depending on the measured thickness. Critical situations can prevail with just a few centimetres of snow, as of which most aircraft are no longer certified for landing. At present, manual measurements are carried out at certain runway points. These measurements must be performed as rapidly as possible to avoid prolonged runway closures, which are always very burdensome in terms of time and money. In addition, manual measurements at a few points do not always offer the required representativeness. The project presented here consists in measuring snow thicknesses ranging from a few millimetres to a few tens of centimetres with an accuracy of the order of 0.3 cm, by means of a system on board a runway service vehicule. The project is conducted by Meteo-France for the needs of Aeroport De Paris (ADP). The prototype is composed of a small-diameter laser beam directed towards the ground, forming a light spot detected by the CCD camera. On the matrix of the camera, the position of the spot is represented by a luminous intensity peak, and it is the position of this peak that gives the measurement, after appropriate conversion. The system is being tested at the Paris Orly Airport and in French Alps this winter. Conclusive results are obtained for all kinds of snow, including melting snow.