Longwall Retreat and Creep Measurement Based on UWB Radar Imaging Method

The measurement of longwall retreat and creep displacements is of great significance for the safety production of a coal mine. In order to reliably and accurately obtain the longwall retreat and creep displacements, this paper proposes an ultrawideband (UWB) radar imaging method. The bolt plates fixed in the roadway coal wall are imaged as the target points. First, a signal model is built, and a modified nonlinear chirp scaling (NLCS) imaging algorithm is designed to obtain the high-resolution image. Then, the retreat and creep displacements are estimated based on the imaging results. Finally, simulation and experiment are performed. The simulation results show that the radar imaging method is theoretically feasible to measure the retreat and creep displacements. The measurement errors in the experiment are 0.058 m and 0.040 m, respectively. In the experiment, the radar velocity fluctuation and signal attenuation cause the target azimuth and range errors in the imaging results, which makes the measurement errors in the experiment larger than that in the simulation. This method requires no additional roadway information except for the bolt plates fixed in the coal wall. In addition, the signal propagation of UWB radar is rarely affected by the dust and moisture in the harsh environment.