Saturday 19 September 2015

Conclusions and Recommendations from research work



CONCLUSION AND RECOMMENDATIONS

          Effects of roofing materials on propagation of air navigation signal have generally been determined. Firstly the research revealed that roofing materials have little effect on navaids signal strength particularly in the transmission path. However the effects were very significant in the reflective path. Secondly it was found that some materials interacted with navaids signal and caused decrease in received signal strength (RSS) while others caused increase in RSS over similar transmission distance but these effects were not significant. Lastly the research established that roofing materials have no significant effect on wave polarization.

          The highest and lowest mean attenuation occurred at angles of incidence of 90 and 135 degrees respectively. It was shown that the lowest received signal strength occurred on decra material at an angle of 135 degrees while the highest occurred on iron at 90 degrees. The attenuation ratio decreased as the angle of incidence was varied from 0 degrees to 90 degree. The highest and lowest mean reflection occurred at angles of incidence of 90 and 135 degrees respectively. It was shown that the lowest reflected signal strength occurred on clay material at an angle of 135 degrees while the highest occurred on steel at 90 degrees. Generally the reflected received signal ratio increased as angle of incidence varied from 0 degrees to 90 degrees across all materials. It was therefore deduced that angle of incidence has significant effect on navaids signal strength in both transmission and reflective paths.

It has been observed that the interaction of roofing materials with navaids signals has no significant effect on recommended minimum signal strength in the transmission path except in the reflective path. For distances that were considered in these experiments, these materials had no significant effect on transmission distance since the received signal was within the recommended signal strength.

Despite the differences a statistical analysis revealed that roofing materials have little effect on wave polarization. It can be concluded that roofing materials have no significant effect on radiation patterns. Therefore a radiation pattern which is a prime variable in the operation of navaids systems cannot be altered by the presence of roofing materials in the propagation path.
Further results showed that there was a strong negative correlation (r = -0.9944) between attenuated and reflected signals at various angles assuming constant effect of roofing material. This implies that angles that provide high attenuation exhibit low reflections and vise versa when material-type is constant. A correlation factor of 0.9611 showed that there was a strong positive correlation between attenuated and reflected signals across roofing materials assuming a constant angle of incidence. It implies that materials that provide high attenuation exhibit high reflections at constant angle,

Relationship between path loss exponent of a roofing material and transmission distance need to be studied further so as to explain why there is a mix of positive and negative correlation.

Further studies should be directed in conducting experiments in open fields and factoring in sources of variability arising from the environment so as to actualize the scenario of flight navigation.
It is also recommended that similar studies should be conducted on roofing materials other than those considered in this research.

Wednesday 16 September 2015

Effects of roofing materials on propagation of air navigation signals



Summary
The findings of this study concur with Laws of Kenya civil aviation act number 21 (2013) on restriction of structures around designated operational areas of aerodromes and flight paths. It also concurs with International Civil Aviation Organization annex 14 Vol.1 (2009) on civil aviation security regulations for protection of airports, aircrafts and navigation facilities. This concurrency means that highly reflective roofing materials are significant hazards to air transport.  According to NIST and Pauli et al (2008), metals offer higher reflectance to radio signals than non-metallic materials which offer higher absorption. This study generally concurs that metals reflect more than non-metals. The findings show that decra, steel and aluminum are the most reflective. Plastic iron and clay are least reflective.  Decra is a metal alloy coated with stone dust. A closer look shows that there are shinny metallic pigments in the coating which probably makes it more reflective than aluminum. Iron sheets used in roofing are galvanized (CGI) which probably makes them less reflective than plastic which appears polished and shiny. These two factors make a difference in reflectance trend.
The analysis found that highly reflective materials such as decra and steel have high attenuation effect. High reflection is a major source of interference in Navaids signal transmission especially with the Distance Measuring Equipment where echoes create significant errors in measured distance. Therefore the effect of steel and decra on Navaids signal strength is more significant when compared to all other roofing materials. Clay and iron had least effects on signal strength. Steel and decra are considered unsuitable for use in aerodrome areas therefore not recommended.
But when reflection path was considered, the highest reflected signal strength was offered by steel (87dBmV/M) inclined at 90o and the lowest was offered by clay (29dBmV/M) inclined at 135o. Recalling that reflection is a major cause of multipath interference, it is quite clear that the reflected signal was way above the recommended minimum. Such a strong reflected signal can find its way into the transmission path and cause significant interference on the forward signal strength (Selex Inc., 2009). International Civil Aviation Organization has specified that the minimum Desired to Undesired (D/U) signal ratio should be 20 dB for air-ground communication systems (ICAO, 2012). All the roofing materials in this study fall below this specification even though iron, clay and plastic have better values compared to aluminum, steel and decra. However aluminum exhibits unique characteristics whereby its D/U value is 0 dB. It means that aluminum propagates and reflects in equal proportions. The study also showed that the major component of the undesired signal is due to reflection. Compared with the recommended minimum D/U, it was established that roofing materials have significant effects on navaids signal strength.

Effects of roofing materials on Navaids wave polarization


Effects of roofing materials on Navaids wave polarization at constant angle

Figure show that iron and clay have the highest horizontal polarization response. It means that horizontally polarized Navaids signals are better propagated via iron and clay than other roofing materials. The figure further shows that vertically polarized signals are better propagated in plastic and clay than in any other material. It also shows that circularly polarized signals are best propagated in plastic roofing materials than all the rest.  However the figure does not provide evidence about significant differences between these materials. When assuming that the effect of angle of incidence is constant, the ANOVAs 2-factor analysis results showed that Fcrit> F-value and the range of P-value is 0.05<P<0.95 for a 2-tailed test when polarization columns were considered. This implies that there is sufficient evidence to state that the three polarization methods do not have a significant difference. However there is evidence to show that at least one pair of the material types differ. Which particular pairs differ remains the same as deduced in section 4.1 since it had been shown here that the horizontal polarization used has no significant difference from the other polarizations. See appendix C for statistical analysis.



Effects of angle of incidence on wave polarization