EFFECTS OF SELECTED ROOFING MATERIALS ON AIR NAVIGATION SIGNAL PROPAGATION

Abstract 

Effects of Roofing Materials on Air Navigation Signal Propagation

The environment around radio navigation aids (navaids) includes buildings whose roofing materials interfere with air navigation signal propagation. This interference may cause partial loss of intelligence in communication between navaids and flying aircrafts. Buildings around airports have been restricted partly because they pose threats to flight navigation. This restriction as captured in the Laws of Kenya has not been supported by sufficient data. Previous studies have shown that about half of air accidents occur during landing. No data has however been availed to determine the contribution of navaids to these accidents. The purpose of this research was to study effects of roofing materials on air navigation signal propagation. The method involved use of a 9.4GHz transmitter, a receiver and a computer to measure signal level transmitted through roofing materials at various angles of incidence. The study considered effects of decra (aluminum-zinc stone-chip coated steel), iron, steel, aluminum, plastic and clay materials on navaids signal strength, transmission distance and wave polarization. The study found that decra offered the highest attenuation whereby 90% of the signal propagated was lost, out of which 60% was due to reflection. This result translated into transmission path signal strength of 57dBmV/M against an International Civil Aviation Organization (ICAO) recommended minimum specification of minus 28dBmV/M. Decra also exhibited the lowest desired-to-undesired signal ratio of minus 16dB which is far below ICAO recommended value of 20dB. Therefore roofing materials had little effect on navaids signal strength in the transmission path but were very significant in the reflective paths. The study found that roofing materials had no significant effect on transmission distance and wave polarization. It was noted that the signal strength depended on angle of incidence. The six roofing materials especially decra and steel had significant effects on signal strength and thus are not recommended for use in aerodrome areas. Based on these findings, building industry and flight navigation authorities have been challenged to develop a compromise roofing material that has little effect on navaids signal propagation. Further studies should be directed in conducting these experiments in open fields so as to actualize the scenario of flight navigation.