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Proceedings Paper

Prototyping for the Spectropolarimeter for Planetary EXploration (SPEX): calibration and sky measurements
Author(s): Gerard van Harten; Frans Snik; Jeroen H. H. Rietjens; J. Martijn Smit; Jozua de Boer; Renia Diamantopoulou; Otto P Hasekamp; Daphne M. Stam; Christoph U. Keller; Erik C. Laan; Ad L. Verlaan; Willem A. Vliegenthart; Rik ter Horst; Ramón Navarro; Klaas Wielinga; Sandro Hannemann; Scott G. Moon; Robert Voors
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Paper Abstract

We present the Spectropolarimeter for Planetary EXploration (SPEX), a high-accuracy linear spectropolarimeter measuring from 400 to 800 nm (with 2 nm intensity resolution), that is compact (~ 1 liter), robust and lightweight. This is achieved by employing the unconventional spectral polarization modulation technique, optimized for linear polarimetry. The polarization modulator consists of an achromatic quarter-wave retarder and a multiple-order retarder, followed by a polarizing beamsplitter, such that the incoming polarization state is encoded as a sinusoidal modulation in the intensity spectrum, where the amplitude scales with the degree of linear polarization, and the phase is determined by the angle of linear polarization. An optimized combination of birefringent crystals creates an athermal multiple-order retarder, with a uniform retardance across the field of view. Based on these specifications, SPEX is an ideal, passive remote sensing instrument for characterizing planetary atmospheres from an orbiting, air-borne or ground-based platform. By measuring the intensity and polarization spectra of sunlight that is scattered in the planetary atmosphere as a function of the single scattering angle, aerosol microphysical properties (size, shape, composition), vertical distribution and optical thickness can be derived. Such information is essential to fully understand the climate of a planet. A functional SPEX prototype has been developed and calibrated, showing excellent agreement with end-to-end performance simulations. Calibration tests show that the precision of the polarization measurements is at least 2 • 10-4. We performed multi-angle spectropolarimetric measurements of the Earth's atmosphere from the ground in conjunction with one of AERONET's sun photometers. Several applications exist for SPEX throughout the solar system, a.o. in orbit around Mars, Jupiter and the Earth, and SPEX can also be part of a ground-based aerosol monitoring network.

Paper Details

Date Published: 9 September 2011
PDF: 12 pages
Proc. SPIE 8160, Polarization Science and Remote Sensing V, 81600Z (9 September 2011); doi: 10.1117/12.893741
Show Author Affiliations
Gerard van Harten, Sterrekundig Instituut Utrecht (Netherlands)
Frans Snik, Sterrekundig Instituut Utrecht (Netherlands)
Jeroen H. H. Rietjens, SRON Netherlands Institute for Space Research (Netherlands)
J. Martijn Smit, SRON Netherlands Institute for Space Research (Netherlands)
Jozua de Boer, Sterrekundig Instituut Utrecht (Netherlands)
Renia Diamantopoulou, Sterrekundig Instituut Utrecht (Netherlands)
Otto P Hasekamp, SRON Netherlands Institute for Space Research (Netherlands)
Daphne M. Stam, SRON Netherlands Institute for Space Research (Netherlands)
Christoph U. Keller, Sterrekundig Instituut Utrecht (Netherlands)
Erik C. Laan, TNO Science and Industry (Netherlands)
Ad L. Verlaan, TNO Science and Industry (Netherlands)
Willem A. Vliegenthart, TNO Science and Industry (Netherlands)
Rik ter Horst, NOVA-ASTRON (Netherlands)
Ramón Navarro, NOVA-ASTRON (Netherlands)
Klaas Wielinga, Mecon Engineering B.V. (Netherlands)
Sandro Hannemann, cosine (Netherlands)
Scott G. Moon, cosine (Netherlands)
Robert Voors, Dutch Space (Netherlands)


Published in SPIE Proceedings Vol. 8160:
Polarization Science and Remote Sensing V
Joseph A. Shaw; J. Scott Tyo, Editor(s)

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