David T. Blewett1,+, Goran Basic2,3, Andrew A. Knuth1, Jordan R. Wiker1, Janine Newhook3, Brett W. Denevi1, Parvathy Prem1, and Hiroyuki Sato41Planetary Exploration Group, Johns Hopkins University Applied Physics Laboratory, USA. 2RobotWorks Corp., Canada. 3Canadensys Aerospace Corp., Canada. 4Japan Aerospace Exploration Agency (JAXA), Japan.(+david.blewett@jhuapl.edu)

Selected ReferencesPhase-ratio Analysis:Blewett et al. (2014), Phase-ratio images of the surface of Mercury: Evidence for differences in sub-resolution texture, Icarus 242,

142.Clegg-Watkins et al. (2016), Photometric characterization of the Chang'E-3 landing site using LROC NAC images, Icarus 273, 84.Kaydash et al. (2012), Phase-ratio imagery as a planetary remote-sensing tool, J. Quant. Spec. Rad. Transfer 113, 2601.Kaydash et al. (2014), Dark halos and rays of young lunar craters: A new insight into interpretation, Icarus 231, 22.Shkuratov et al. (2013), Lunar surface traces of engine jets of Soviet sample-return probes: The enigma of the Luna-23 and Luna-

24 landing sites, Planet. Space Sci. 75, 28.Lunar Polarimetry:Dollfus (1998), Lunar surface imaging polarimetry: I. Roughness and grain size, Icarus 136, 69.Jeong et al. (2017), Preliminary design of wide-angle polarimetric camera for the first Korean lunar mission, 3rd Planetary Data

Workshop, LPI Contrib. no. 1986, abstr. 7035.Jeong et al. (2018), Multi-band polarimetry of the lunar surface. II. Grain size evolutionary pathway, Astrophys. J. 869, 67.Kim et al. (2017), Laboratory measurements of light polarization on samples targeted for the lunar regolith, Adv. Space Res. 59,

1629.Shkuratov et al. (2017), Interpreting lunar polarimetric anomalies at large phase angles, Icarus 296, 117.

LPSC 51st - Abstract no. 1322

Imaging the reflectance and polarization behavior of granular materials

Construction of a Goniometer Instrument for Imaging Polarization and Photometric Studiesof Planetary Regolith Analogs

Introduction• Phase-ratio analysis is a

technique to obtain sub-resolution information about the texture and scattering behavior of planetary surfaces.

• There is also growing interest in imaging polarimetry as a planetary remote-sensing technique. The Korea Pathfinder Lunar Orbiter(KPLO) will collect global multispectral/multi-polarization images of the Moon.

• More laboratory work is needed to help link photometric and polarization parameters to the physical properties of planetary regoliths.

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A New Lab Facility• The Planetary Surface Texture Lab (PSTL) is

based on a imaging polarimeter, going beyond the spot measurements of most current facilities.

• A goniometer will move the polarimeter and a light source through a range of illumination (i), viewing (e), and phase (g) angles.

• Regolith analog materials will be characterized in terms of particle size-frequency distribution and shape.

• The comprehensive data in (i, e, g) space will be used for photometric modeling, e.g., fitting of Hapke parameters that can be linked to the known particle properties such as albedo, size, and shape. We also plan to test empirical relations that connect particle size to polarization, and to develop radiative-transfer code that includes the four Stokes polarization parameters and allows for incorporation of particle size, packing, and shape.

• PSTL is expected to take first light in May 2020.

Schematic of the goniometer operation, not to scale.

Phase-ratio image (76o/36o) of the Apollo 11 site. The high ratios around the lander indicate modification of the

regolith by rocket exhaust, interpreted as a decrease in small-scale roughness. Data from PSTL

will help to quantify this interpretation.

Test data collected with the polarimeter and light source mounted on tripods.

A. Image of sample trays in 45o light. i= 43o, e = 70.6o, g = 114o.

B: Polarization ratio 45o/90o. JSC-1A is a lunar mare soil simulant. Trays are 18 cm wide.

Shkuratov et al. (2013)

CAD rendering of the PSTL goniometer. The arc radius is 1.5 m.

Motorized caddies carry the polarimeter and light source. Samples are placed on the the central stage.

The imaging polarimeter simultaneously captures co-registered images in three polarization states.

The goniometer is being designed and built by Canadensys Aerospace under license from RobotWorks.