Subsurface imaging with a voice-coil portable active seismic source and a single geophone: From field validation to lunar application

• Voice-coil portable active seismic source (PASS) for lunar subsurface imaging. • PASS enables continuous signals, enhancing S/N for both body and surface waves. • 2D/3D S-wave velocity profiles (∼7m depth) derived from surface-wave analysis. • P-wave tomography and reflection imaging resolve subsurface structures to ∼80 m. • Space-qualified PASS supports astronaut and rover deployment in future missions. To image and characterize the lunar subsurface, we have developed an active seismic exploration system that combines a single ultra-compact seismic source with a single geophone. The seismic source employs a voice-coil actuator, a type of linear electromagnetic motor, which minimizes the source mass while maintaining a nearly constant force of ∼10 N over a wide frequency range. Despite its compact size of less than 800 g, the source can emit seismic signals repeatedly. Stacking the repeated signals enhances the signal-to-noise ratio, allowing both body-wave and surface-wave propagation over source–receiver distances exceeding 60 m, as demonstrated in field tests at Mount Fuji. When the seismic source is operated at multiple locations around a fixed geophone, astronauts or rovers can acquire multichannel-equivalent seismic datasets. This configuration enables retrieval of 2D or 3D S-wave velocity profiles to depths of ∼7 m through surface-wave analysis. In contrast, when both the seismic source and the geophone are mounted on separate rovers and moved independently, the system allows flexible multi-shot and multi-receiver acquisition geometries. This configuration enables body-wave-based seismic refraction and reflection surveys, allowing refraction tomography to derive 2D P-wave velocity models and reflection analysis to image subsurface structures to depths of ∼80 m. Finally, we optimized these systems and adapted them for space applications, enabling deployment by astronauts and integration with rovers in future space missions.