Underground transient electromagnetic real-time imaging system for coal mine water disasters

•We developed a wireless antenna attitude angle measuring instrument based on an electronic compass, which measures antenna attitude angle of underground transient electromagnetic instrument automatically and real-time.•The current transmission, signal acquisition, and antenna rotation angle information are automatically achieved for real-time imaging.•The direct algorithm of the apparent resistivity of the whole-space transient electromagnetic field in overlapping loop mode based on double-logarithmic-transform piecewise least-squares fitting, which not only ensures accuracy but also accelerates calculation.