Enabling Techniques For Runways Quality Surveillence Via Ground Penetrating Radar

With the rapid development of runways construction, the quality problem ofrunways is a serious hidden trouble for the safety of aviation. In the dissertation, thekey techniques concerned in the field of runways surveillance based on GroundPenetrating Radar (GPR) are studid. The main contents consist of the echo simulationof electromagnetic (EM) wave propagated in the pavement structure of runways, theEM properties inversion of the pavement structure and the thickness calculation ofvoid disaster in runways.The main achievements and conclusion of this paper are summarized asfollows:1. The propagation model and non-constant–Q attenuation model of the transmittedEM wave in the loss multilayer media are studied. A GPR echo simulation methodbased on non-constant-Q attenuation model is proposed.and the echo signal modelof EM wave propagated in the dispersive loss media layers is constructed. Theproposed echo simulation method is better than FDTD method based on Maxweillfunction in calculation burden, and is wider than that based on constant-Qattenuation model in the applied area.2. Based on the propagation model of EM wave propagated in the pavementstructiure, the EM properties and depth inversion method based on systemidentification theory is also struded. Firsty, based on the conventional systemidentification method to be used to estimate real part and imaginary part of thecomplex permittivity, a new permittivity and conductivity inversion method basedon the improved system identification is proposed, in which the effect of thefrequency proponents within the transmitted band width on the imaginary part ofcomplex permittivity is considered. Secondly, The EM property of multilayermedia containing the thin layer are intensively given, in which a super resolutionparameter estimation method,WRELAX, is introduced to estimate the time delayof echo. Finally, as far as the EM property inversion of the reinforcing steel bararea in runways is concerned, the bar suppression algorithm based onHyp-cruvelet transform is studied, and then the EM property are estimated basedon the bar suppressed data. 3. The detection method of the void disaster based on the time-frequency distributioncharacteristic of S transform is proposed. The void layer is thin layer, whosethickness is less than1cm, and so for the current GPR system, the void thin layercan not be detected only by the time resolution. S transform is a time-frrequencytool in whch the Gaussian window width is inverse proportion to the frequency.The S transform of the echoes reflected from the the void layer are aliased andeffected each other. S transform has higher frequency resolution in the lowerfrequency, where the variance of the S transform can be detected. Therefore thevoid layer can be detected by the distortion of the bottom part of S transformobtained by the reflected echoes.4. For the non-destructive detection characteristic of GPR, the void thicknessestimation algorithms based on the upper-shifted peak frequency property of theechoes and spectrum optimization inversion are studied. For the above twomethods, the impulse pair in the time domain corresponding to the upper andbottom interface of void-layer are needed. For the non-destructive GPR system,the received signal is the reflected echo of the EM wave propagated in thepavement structure (including the void layer). So the impulse pair in the timedomain corresponding to the upper and bottom interface of void-layer are neededto be extracted. In this dissertation, they are extracted based on the EM wavepropagation model and system identification method studied in the forgoingchapers, then the void layer thickness is calculated based on the upper-shifted peakfrequency property and spectrum optimization inversion algorithm.