Marco Pirozzoli, U.S. Air Force Academy; Lucy Zimmerman, U.S. Air Force Academy; Michael Korta, U.S. Air Force Academy, Adrian Scheppe, U.S. Air Force Academy; Michael Plummer, U.S. Air Force Academy; Francis Chun, U.S. Air Force Academy; David Strong, U.S. Air Force Academy
Keywords: Instrumentation (Sensors and Systems), Polarimetry
Abstract:
The Department of Physics at the United States Air Force Academy has a DFM Engineering f/8.2, 16-inch telescope outfitted with a 9-position filter wheel populated with broadband photometric filters (Johnson-Cousins B, V, R, and a blue-blocking exoplanet filter) and a 100 lines per millimeter diffraction grating. As part of their senior capstone project, physics cadets developed a simple, four-channel polarimeter by populating the open slots in the filter wheel with linear polarized filters oriented at 0°, 45°, 90°, and 135° relative to the vertical axis of the imaging camera. Size and weight restrictions on the back of the telescope prohibited the use of more elaborate polarimeters. We developed the process and procedures to characterize the effect of the telescope optical elements on the polarization of incident light. Using an unpolarized, uniform flat light source, along with a polarized film rotated at 10° increments from 0° to 180°, the intensity of the light source was measured as it passed through the entire optical system including the as before mentioned linear polarized filters. The measured intensities were fitted to Malus Law using a least squares method. From this fit, a modified Mueller matrix was created that describes how the telescopes optical elements, including the polarizing filters, alter the incident light measured by the telescopes camera. In order to relate the measured intensities of light to the Stokes parameters of the light reflected from a satellite, a calibration matrix was computed using a pseudoinverse of the modified Mueller matrix. The sensitivity of the pseudoinverse process was analyzed by perturbing input data and measuring the RMS error between the perturbed and ideal matrices. This process for employing the pseudoinverse introduced minimal error into the system as the RMS error for the calibration matrix was within an acceptable error range. The calibration matrix was applied to satellite observations taken during the Fall 2019 equinox period and resulted in observed satellite Stokes parameters.
Date of Conference: September 15-18, 2020
Track: Optical Systems & Instrumentation