Physics – Optics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p11f1635s&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P11F-1635
Physics
Optics
[0305] Atmospheric Composition And Structure / Aerosols And Particles, [0343] Atmospheric Composition And Structure / Planetary Atmospheres, [3311] Atmospheric Processes / Clouds And Aerosols, [6297] Planetary Sciences: Solar System Objects / Instruments And Techniques
Scientific paper
We present SPEX, the Spectropolarimeter for Planetary Exploration, which is a compact, robust and low-mass multi-viewing angle spectropolarimeter designed to operate from an orbiting satellite platform. Its purpose is to simultaneously measure, with high accuracy, the radiance and the state (degree and angle) of linear polarization of sunlight that has been scattered in a planetary atmosphere or reflected by a planetary surface. The degree of linear polarization is extremely sensitive to the microphysical properties of atmospheric or surface particles (such as size, shape, and composition), and to the vertical distribution of atmospheric particles, such as cloud top altitudes. Measurements as those performed by SPEX are therefore crucial and often the only tool for disentangling the many parameters that describe planetary atmospheres and surfaces. SPEX uses a novel, passive method for its radiance and polarization observations that is based on a carefully selected combination of polarization optics. This results in a modulation of the radiance spectrum in both amplitude and phase by the degree and angle of the linear polarization spectrum, respectively. The polarization optics consists of an achromatic quarter-wave retarder, an a-thermal multiple-order retarder, and a polarizing beam splitter. Such a configuration is implemented for a range of viewin directions, which allows sampling the full scattering phase function of each ground pixel under investigation, while orbiting the planetary body. The present design of SPEX is tuned to a Mars mission, as a payload on a satellite in a low orbit. However, the concept is perfectly applicable for Earth remote sensing from an orbiting platform like ISS or a dedicated mission, for which we are developing a breadboard. A similar concepts is under study for a mission to the Jovian system including the Galilean Moons. We will show first test results obtained with recently developed prototype of the SPEX instrument, demonstrating excellent performance and overall behavior as compared with design parameters and SPEX instrument simulator. In addition, we present results of multi-angle spectropolarimetric measurements of the Earth's atmosphere from the ground in conjunction with one of AERONET's sun photometers.
Hasekamp O. P.
Moon Sungwook
Rietjens J.
Smit Martijn J.
Snik Frans
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