Research On Parameter Estimation Method Of Multi-path Target For Downhole Broadband Radar

Coal industry is an important pillar of our country’s socioeconomic development and energy strategic planning,Before coal mining,the use of ground penetrating radar technology to finely detect unfavorable geological anomalies in coal seams is a powerful guarantee to ensure safe and efficient production of coal mines.The spatial stepped frequency radar is an ultrawideband ground penetrating radar that combines the multi-transmit and multi-receive array system and the stepped frequency signal.It can obtain a large bandwidth and aperture at the receiving end of the array,and has good ranging and angle measurement performance.However,there are serious multi-path effects and non-Gaussian impulse noise in the actual mine environment,which lead to a sharp drop in the detection performance or even failure of the spatial stepped frequency radar.Therefore,this paper conducts research on the detection method of coal seam heterogeneous bodies under the environment of multi-path and impulse noise.The main research contents are as follows:1.Aiming at the coal seam heterogeneous target,a multi-path receiving signal model of the spatial stepped frequency radar is established,and the reflection coefficient of the electromagnetic wave in the coal seam medium is calculated.In addition,the a stable distribution is used to establish the downhole impulse noise signal model.2.Aiming at th e problem that the estimation performance of spatial stepped frequency radar for coal seam heterogeneity is seriously degraded in multi-path environment,a two-dimensional sparse asymptotic minimum variance(TR-2D-SAMV)estimation method based on time inversion is proposed.Through time-reverse processing of the received signal,the influence of multi-path effect on the echo signal is eliminated;then the 2D-SAMV algorithm is used to search the distance and angle for iterative update,and obtain the accurate estimated value of the target distance-angle parameter.The experimental results show that in the multipath environment with low signal-to-noise ratio and few snapshots,the method can accurately distinguish the direct signal and multipath signal,and has high estimation accuracy for coal seam heterogeneity.3.Aiming at the problem that the estimation performance of spatial stepped frequency radar for coal seam heterogeneity fails in downhole impulse noise and multi-path environment,a Median Difference Correlation Entropy(MCBCM)algorithm based on covariance matrix is proposed to effectively suppress strong impulse noise,and use the TR-2D-SAMV algorithm to correct the phase distortion caused by the multi-path effect,and realize the two-dimensional joint estimation of the target distance-angle parameters.The experimental results show that the proposed MCBCM-TR-2D-SAMV joint algorithm can effectively suppress impulse noise,accurately distinguish direct signal and multipath signal,and realize accurate estimation of coal seam heterogeneity.