Angle-Resolved Terahertz Reflectance of Pure Water and Ice Under HH and VV Polarizations in the 220–500 GHz Range

Accurate characterization of the terahertz (THz) reflectance of pure water and ice is essential for understanding their dielectric behavior and electromagnetic response in the submillimeter wave regime. These insights have significant implications for planetary remote sensing, atmospheric science, and material diagnostics. In this study, we present angle-resolved THz reflectance measurements of pure water and pure ice under two polarization configurations: horizontal (HH) and vertical (VV). Measurements were conducted using a free-space system built around a vector network analyzer (VNA) with frequency extenders, covering two spectral bands: 220–330 GHz and 330–500 GHz. The setup integrates reflective optics including parabolic and elliptical mirrors, two three-reflector polarization rotators, two wire grid polarizers, and a motorized angle arm for controlled variation of incidence angle, while maintaining stable sample positioning. Distinct Brewster angle features were observed and analyzed to probe polarization dependence. For pure water, the measured reflectance shows strong agreement with predictions from a combined double Debye and Fresnel model, yielding coefficients of determination \(R^2\) of 0.997 (VV) and 0.890 (HH). For ice, reflectance simulations based on a semi-empirical dielectric model and Fresnel equations yield moderate agreement, with \(R^2\) values of 0.700 (VV) and 0.648 (HH). These results serve as essential reference data across frequency bands pertinent to planetary missions, supporting the modeling and interpretation of THz remote sensing observations of icy and aqueous environments.