Terahertz characteristics of regolith simulants: Effects of bulk density and water content on electromagnetic response for planetary remote sensing

Electromagnetic properties of regolith are critical for understanding planetary subsurface structure and resource potential. However, their behavior in the terahertz (THz) frequency range remains poorly characterized. THz waves are particularly sensitive to fine-grained structure and hydration state, offering new opportunities for high-resolution planetary subsurface sensing. To investigate these interactions, we performed THz reflection measurements on FJS-1 lunar regolith simulants while varying bulk density (1.44–1.81 g/cm 3 ) and volumetric water content (0–46.1%). Measurements were conducted across 220–500 GHz using dual polarizations (HH, VV) and angle-resolved configurations (20–70° incidence angles). Results show clear density and hydration dependence of THz reflection coefficients, with Brewster angle shifts indicating changes in dielectric contrast. VV polarization demonstrated significantly higher sensitivity to both variables than HH polarization, enabling improved discrimination of subsurface properties. Results provide new experimental constraints on THz wave propagation in granular materials under controlled conditions, establishing a measurement framework applicable to future planetary remote sensing strategies for landing site assessment and water detection. • Terahertz properties of regolith simulants were measured from 220 to 500 GHz using dual-polarization at multiple angles. • Bulk density (1.44–1.81 g/cm 3 ) and water content (0–46.1%) were varied to examine THz response and Brewster angle. • Results provide new constraints on THz propagation in granular media for planetary remote sensing.