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SPEX: The spectropolarimeter for planetary EXploration

Author: Snik, F. · Rietjens, J.H.H. · Harten, G. van · Stam, D.M. · Keller, C.U. · Smit, J.M. · Laan, E.C. · Verlaan, A.L. · Horst, R. ter · Navarro, R. · Wielinga, K. · Moon, S.G. · Voors, R.
Type:article
Date:2010
Source:Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave, 27 June 2010 through 2 July 2010, San Diego, CA, USA. Conference code: 81848, 7731
series:
Proceedings of SPIE - The International Society for Optical Engineering
Identifier: 425159
ISBN: 9780819482211
Article number: No.: 77311B
Keywords: Physics · Aerosols · Dust · Mars · Spectropolarimetry · A-thermal · Atmospheric particles · Cloud particles · Entrance pupil · Flight direction · Ground pixels · Ice clouds · In-orbit · Incoming light · Intensity spectrum · Jupiters · Limb-viewing · Linear polarization · Mars · Martian dust · Microphysical property · Moving parts · Multiple-order retarders · Optical and mechanical designs · Performance simulation · Planetary atmosphere · Planetary exploration · Polarization scattering · Polarizing beam splitters · Quarter waves · Single-intensity · Sinusoidal modulation · Spectral dependences · Spectropolarimeters · Spectropolarimetry · Atmospheric aerosols · Atmospheric composition · Clouds · Earth (planet) · Instruments · Interplanetary flight · Interplanetary spacecraft · Millimeter wave devices · Millimeter waves · Optical telescopes · Polarization · Space telescopes · Vehicular tunnels · Dust · Industrial Innovation · Physics & Electronics · OPT - Optics · TS - Technical Sciences

Abstract

SPEX (Spectropolarimeter for Planetary EXploration) is an innovative, compact instrument for spectropolarimetry, and in particular for detecting and characterizing aerosols in planetary atmospheres. With its ∼1-liter volume it is capable of full linear spectropolarimetry, without moving parts. The degree and angle of linear polarization of the incoming light is encoded in a sinusoidal modulation of the intensity spectrum by an achromatic quarter-wave retarder, an athermal multiple-order retarder and a polarizing beam-splitter in the entrance pupil. A single intensity spectrum thus provides the spectral dependence of the degree and angle of linear polarization. Polarimetry has proven to be an excellent tool to study microphysical properties (size, shape, composition) of atmospheric particles. Such information is essential to better understand the weather and climate of a planet. The current design of SPEX is tailored to study Martian dust and ice clouds from an orbiting platform: a compact module with 9 entrance pupils to simultaneously measure intensity spectra from 400 to 800 nm, in different directions along the flight direction (including two limb viewing directions). This way, both the intensity and polarization scattering phase functions of dust and cloud particles within a ground pixel are sampled while flying over it. We describe the optical and mechanical design of SPEX, and present performance simulations and initial breadboard measurements. Several flight opportunities exist for SPEX throughout the solar system: in orbit around Mars, Jupiter and its moons, Saturn and Titan, and the Earth. © 2010 SPIE.