[PEM14-P35] Observation of auroral polarization using a polarization imaging spectrometer in Alaska
Keywords:aurora, polarization, spectroscopy
In addition to auroral polarization, measurement data involve polarization effects due to atmospheric scattering, acrylic domes and optical system in the instrument (hereinafter referred to as instrumental polarization). Therefore, it is a key to carry out to obtain precise calibration data to correct the instrumental polarization. Although we have performed auroral polarization measurements since 2013, we got a problem in the calibration instrument and then did not obtain sufficient calibration data. In this study, we develop a new calibration instrument with a LED lamp monitoring the rotation angle of linear polarizer and succeeded to obtain the precise calibration data to correct the instrumental polarization. We also developed the data analysis method to apply the calibration data to measurement data to estimate the auroral polarization accurately.
We installed this instrument at Pokar Flat Research Range, Alaska in November of 2015 and took many calibration data for various field-of-view during our stay for about two weeks. As a result, calibration data with a quantitative accuracy better than 0.2 percent was obtained. Auroral polarization measurement continued till March of 2016. For a case of auroral polarization on November 19, 2015, the linear polarization degree of 630 nm aurora was 1.6 +/- 0.9 percent. For most cases, polarization degree showed a tendency that maximized at the low elevation angle toward the magnetic north, and decreases as the elevation angle increases. In addition, it showed that polarization degree increases again around the magnetic zenith toward the low elevation angle side in the magnetic south. We also obtained that the auroral linear polarization increases during auroral active period.