Abstract: To address the problem that traditional source depth estimation methods fail due to the low signal-to-noise ratio of broadband continuous-spectrum signals in the shadow zone of deep water, two source depth estimation methods are proposed using the narrowband range-dimensional interference structures of the acoustic field. When both the source and the receiver are located near the sea surface, two types of narrowband range-dimensional interference structures can be observed at the receiver in the first shadow zone, arising from the coherent superposition of four kinds of single bottom-reflected rays, and these structures are associated with two types of multipath arrival time delays, respectively. In this paper, the analytical expressions of the above two time delays are simplified, and the relationships between the narrowband range-dimensional interference spacings of the two interference structures and the source position as well as the receiver depth are derived for the acoustic field excited by an underwater source. Based on these relationships, two single-hydrophone source depth estimation methods are proposed using the narrowband range-dimensional interference spacings. Compared with existing methods, the proposed methods can be applied to both broadband impulsive sources and narrowband line-spectrum sources, and do not require replica field computations. Experimental data validation shows that within the source range of 20 km to 37 km, the estimation errors of both methods do not exceed 18% for both broadband and narrowband scenarios.