Title
Prototyping for the Spectropolarimeter for Planetary EXploration (SPEX): calibration and sky measurements
Author
van Harten, G.
Snik, F.
Rietjens, J.H.H.
Smit, J.M.
de Boer, J.
Diamantopoulou, R.
Hasekamp, O.P.
Stam, D.M.
Keller, C.U.
Laan, E.C.
Verlaan, A.L.
Vliegenthart, W.A.
ter Horst, R.
Navarro, R.
Wielinga, K.
Hannemann, S.
Moon, S.G.
Voors, R.
Publication year
2011
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.
Subject
Remote sensing
Spectral modulation
Spectropolarimetry
A-thermal
AERONET
Aerosol monitoring networks
Birefringent crystals
Calibration tests
Degree of linear polarization
End-to-end performance
Field of views
Ground based
High-accuracy
In-orbit
Intensity spectrum
Planetary exploration
Polarization spectra
Polarizing beam splitters
Quarter waves
Retardance
Single scattering
Sun photometers
Vertical distributions
Atmospheric aerosols
Earth (planet)
Modulation
Optimization
High Tech Systems & Materials
Industrial Innovation
Physics & Electronics
SSE - Space Systems Engineering
TS - Technical Sciences
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TNO identifier
443002
ISBN
9780819487704
ISSN
0277-786X
Source
Polarization Science and Remote Sensing V, 21-22 August 2011, San Diego, CA, USA
Series
Proceedings of SPIE - The International Society for Optical Engineering
Document type
conference paper