Broadband very-high frequency (VHF) localization of lightning radiation sources provides an important means for understanding lightning discharge characteristics and the corresponding physical mechanisms. In order to improve the ability to locate weak radiation sources, the orthogonal propagator method (OPM) is proposed to map the space-time evolution process of lightning discharge channels based on the theory of spatial spectrum estimation. In the method, the linear decomposition of the covariance matrix is used to form the orthogonal propagator, and the spatial spectrum is constructed according to orthogonality of subspaces. Then, the location of lightning radiation sources is determined by searching for the maximum of the spatial spectrum. For broadband VHF signals, the non-coherent subspace method is used to average the effective frequency points in bandwidth to reduce noise interference. Based on a multiple-antenna radiation continuous observation system (MARCOS), locating performance of the method is analyzed by numerical simulation. The method is verified by parameters such as locating error, half-peak width of the spatial spectrum, and angular resolution. Compared with the results from the time reversal technique(FDTR), the location error and recognition probability under a low signal to noise ratio (SNR) of the proposed OPM algorithm are similar to those of FDTR algorithm, but the angular resolution for two radiation sources of OPM algorithm is better than that of FDTR algorithm. Finally, the proposed method is used to map the spatial and temporal development of a classical triggered lightning discharge channels in the summer of 2017. The results show that the proposed method can clearly depict the basic structure of lightning discharge channels with high spatial and temporal resolution. For the upward positive leader of the triggered lightning, the OPM algorithm can locate more radiation sources with a better structure than the FDTR algorithm. It implies that the proposed OPM algorithm is better for locating weak radiation sources than the FDTR algorithm. Meanwhile, the OPM algorithm has better performance for resolving two radiation sources in the same window than the FDTR algorithm. As a result, the proposed OPM method is of great significance for improving the application value of broadband VHF arrays in the study of locating weak radiation sources and lightning initiation mechanisms.