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. 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.
An InfraRed Channeled Spectro-Polarimeter (IRCSP) was demonstrated in the near space environment as a piggyback out of NASA Columbia Scientific Ballooning Facility. The compact IRCSP is sensitive to linearly polarized long-wave infrared (LWIR) light between 7-12 microns and targets cloud micro-physical properties. Post landing the instrument was retrieved with no damage to the optical payload and collected over 150 minutes of flight data at altitudes above 30 km. The results collected both demonstrate the operation of uncooled microbolometers in the low pressure environment and are the first know high-altitude observations of a polarized signal from cloud tops in the LWIR. During deployment, the IRCSP reported brightness temperatures between 250-285K with uncertainty of < 1:5K. In addition, statistically significant polarization modulation with degrees of linear polarization (DoLP) between 1 – 20% and preferential angle of linear polarization (AoLP) trends were detected. These results support the hypothesis that the LWIR polarimetry has the potential to add new sensitivity to existing remote sensing platforms.
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