Differences in Ice and Water LWIR Spectral Polarimetry at Room Temperature

The University of Arizona Polarization Lab developed an Infrared Channeled Spectro-Polarimeter (IRCSP) to measure linear Stokes parameters with 1K polarimetric accuracy and 1µm average spectral resolution between 8-11µm.^1-3 Emissivity and refractive index in this spectral band are known to depend upon water's kinetic temperature and thermodynamic phase. In this work, the theoretical thermodynamic phase discrimination capabilities of spectral Long-Wave-Infrared (LWIR) polarimetry are demonstrated with IRCSP. In a room temperature laboratory environment, IRCSP measurements of melting ice are shown to depend on the view angle, wavelength, and thermodynamic phase. As the solid ice melted for 10 minutes, IRCSP measured a constant brightness temperature of 276K between the time-lapsed samples. The difference in the degree of linear polarization (DoLP) between solid and melted ice was 7% on average and peaked at 13% in the 9.5-10.5µm waveband. This observation is an example of enhanced sensitivity to thermodynamic phase change using LWIR polarimetry.