Study On Signal Processing Method Of Elastic Wave Ground Penetrationg Radar In Coal Seam

This thesis is based on the National Natural Science Foundation of China, "the theoretical study of coal seam reflection wave trough fine sounding based on continuous source".The main purpose of this paper is on processing the ultra low frequency elastic wave signal, includeing the cancellation and noise elimination of direct wave interference and interface interference,and the extraction of different reflection characteristics of signal submerged in the distal middle and small structure characteristic signal.The propagation characteristics of ultra low frequency elastic waves in coal seam are analyzed. The complex structure of the coal bearing strata, resulting in elastic wave will be affected by multipath effect in the process of communication, and producing wave propagation delay and the attenuation of signal amplitude energy, so the receiver signal is often the weak signal attenuation.The received echo signal has some non causal characteristics, and the direct wave interference, the gradient noise interference and the low frequency signal, the wave growth and the interference of the interface are serious.However, in the practical engineering detection, the received echo signal, in addition to the interference of high interference and multi interface interfer-ence,homologous interference is the key factor that affects the small structure feature.A low frequency multi interface signal model is established, and the non causal filter structure NLMS cancellation algorithm is selected for interference suppression. According to the received signal characteristics and interference characteristics, in order to reduce steady-state error and improve the convergence speed,the selection of step size is improved,the new Sigmoid function is used to change the step size,, and it is applied to the adaptive cancellation of the non-causal variable step size.Because only the use of cancellation can not reach the actual application effect,it is necessary that the received signal is processed two times in order to extract the weak signal of the small structure in the far end. According to the characteristics of blind source separation which can separate multiple source signals, the combination algorithm of blind source separation and adaptive cancellation is proposed. First, we use blind source separation to separate strong signal components and use this signal as negative feedback signals.The simulation results show that the improved algorithm proposed in the third chapter can obtain better cancellation effect under the condition of smaller steady-state error and faster convergence speed. The signal processing is carried out. The simulation results show that the proposed hybrid algorithm in the fourth chapter can eliminate most of the homologous interference, especially the strong component,and the characteristics of the small structure are obvious in the echo profile...