The generation of panoramic borehole images from side-view borehole videos in underground coal mines

Borehole scoping is widely used in U.S. underground coal mines for stability analysis and geological mapping. Traditionally, an experienced geologist is required on-site to characterize the lithology during borehole scoping. However, panoramic images generated from recorded borehole videos can provide comprehensive information about in-situ structures along borehole walls. Extensive studies have focused on generating and analyzing panoramic borehole images using front-view borescopes. However, side-view borescopes are predominantly used in U.S. underground coal mines. This study developed a method to generate panoramic borehole images using a side-view borescope. Unlike a front-view borescope, image stitching for side-view borehole videos begins with optimizing image acquisition frequency to accommodate the wider field of view and applying image cropping to partially correct distortion. The stitching process involved key point detection, key point matching and filtering, offset calculation, and image alignment. The proposed method was tested by stitching a recorded borehole video while varying the parameters of image stitching algorithm. The video frames were successfully stitched into a panoramic image, clearing showing the in-site structures of the borehole walls. Reducing the image acquisition frequency enabled successful stitching but introduced more visible seams in the resulting image. A preliminary parametric study demonstrated that fine-tuning algorithm parameters, combined with controlled borescope movement to minimize image blurriness, can enhance stitching performance and reduce the time required for real-time processing. This work improves the efficiency of geologic mapping by enabling clear visualization of geology along the entire borehole and further helps underground mine operators implement appropriate ground control designs and hazard mitigation techniques, therefore enhancing health and safety of mine workers.