A review on coal-rock identification methods for longwall mining faces and prospective research on 3D interface identification with UWB radar

Coal-rock identification is one of the critical challenges in longwall mining faces. In terms of identification methods, it can be categorized into process signal monitoring, mechanical wave detection, and electromagnetic wave detection. Based on the identification type, it can be further divided into medium identification and interface identification. Addressing the practical need for advanced detection of the trend and orientation of the coal-rock interface for the current and subsequent cuts during shearer operation, and considering the precondition that the coal-rock interface has not been exposed, this study leverages the strong penetration capability and high three-dimensional resolution of ultra-wideband (UWB) radar. It summarizes the existing problems in current identification methods and refines the research content of 3D coal-rock interface identification using UWB radar in fully mechanized mining faces. First, it investigates the UWB electromagnetic wave channel model coupled with the air-coal-rock medium in fully mechanized mining faces, aiming to resolve the mathematical characterization of the channel impulse response, reveal the signal loss and reflection/refraction propagation laws, and obtain a mathematical description of the echo signals. Second, it develops a 3D imaging method for the coal-rock interface using UWB radar in a linear array focusing mode, establishes a 3D imaging model, and reveals the mechanism and influencing factors of inverting the 3D coal-rock interface imaging from the mathematical model of echo signals.