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We provide a brief overview of photometric and polarimetric data of planetary regoliths obtained through telescopic and spacecraft
observations. We apply imaging photometry to study brightness opposition spikes of the Moon and Jupiter satellite Europa.
We also show that the opposition phase curves of lunar sites are almost independent of wavelength...
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... surges also may be present over terrestrial landscapes. Figure 4 shows a photograph taken by one of the authors (YGS) while traveling via airplane over Arizona. To retrieve the phase dependence of brightness from lunar images, we make phase ratio images using data obtained at small and comparatively large phase angles for the same sites [6]. ...
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We present reflectance and polarization phase curve measurements of highly reflective planetary regolith analogues having physical characteristics expected on atmosphereless solar system bodies (ASSBs) such as a eucritic asteroids or icy satellites. We used a goniometric photopolarimeter (GPP) of novel design to study thirteen well-sorted particle...
We present new, detailed polarimetric measurements of the Galilean satellites of Jupiter with U, B, V, and R filters at phase angles ranging from 12° to nearly 0°. The polarization phase curves of Io, Europa, and Ganymede in the B, V, and R filters clearly show the presence of the polarization opposition effect in the form of a sharp peak of negati...
Citations
... Solar light scattered from such objects carries information and physical properties of the upper layer of their surfaces. Measuring intensity and linear polarization as functions of the scattering θ or phase angle α (α = π − θ) one can characterize them and extract the information about the complex refractive index of the material, particles size, packing density and the surface microrelief (e.g., Shkuratov et al. 2002;Videen et al. 2004;Shkuratov et al. 2004;Ovcharenko et al. 2006;Shkuratov et al. 2007a, b;Mishchenko et al. 2010;Kolokolova et al. 2015;Levasseur-Regourd et al. 2015;Nelson et al. 2018;Poch et al. 2018;Muinonen et al. 2015a, b). This method potentially can be applied for characterization of the surfaces of solid exoplanets with no substantial atmospheres if such polarimetric observations are realized (Wiktorowicz and Stam 2015). ...
We review our results of numerical simulations of light scattering from different systems of densely packed irregular particles. We consider spherical clusters, thick layers and monolayers with realistic topologies and dimensions much larger than the wavelength of light. The maximum bulk packing density of clusters is 0.5. A numerically exact solution of the electromagnetic problem is obtained using the Discontinuous Galerkin Time Domain method and with application of high- performance computing. We show that high packing density causes light localization in such structures which makes an impact on the opposition phenomena: backscattering intensity surge and negative linear polarization feature. Diffuse multiple scattering is significantly reduced in the case of non-absorbing particles and near-field interaction results in a percolation-like light transport determined by the topology of the medium. With this the negative polarization feature caused by single scattering gets enhanced if compared to lower density samples. We also confirm coherent double scattering mechanism of negative polarization for light scattered from dense absorbing slabs. In this case convergent result for the scattering angle polarization dependency at backscattering can be obtained for a layer of just a few tens of particles if they are larger than the wavelength.
... This is a debris material represented by dust, broken rocks, and glasses, which is a result of long-time meteoroid bombardment. Solar light scattered from such a surface carries information about the structure and composition of the upper layer, which can be extracted from the corresponding Stokes parameters (e.g., Shkuratov et al., 2002;Videen et al., 2004;Shkuratov et al., 2004;Ovcharenko et al., 2006;Shkuratov et al., 2007a;Mishchenko et al., 2010;Kolokolova et al., 2015;Levasseur-Regourd et al., 2015;Nelson et al., 2018;Poch et al., 2018;Muinonen et al., 2015). Potentially, this technique can be used for detection of details on the surfaces of atmosphereless exoplanets as one can assume that similar weathering processes take place in other planetary systems (Wiktorowicz and Stam, 2015). ...
... Photopolarimetric observations of the objects in the Solar System are usually carried at small phase angles, where backscattering optical phenomena, such as the intensity surge (IS) (Shkuratov et al., 2002;Levasseur-Regourd et al., 2015;Ovcharenko et al., 2006;Nelson et al., 2018;) and the negative polarization (NP) branch, are revealed. These phenomena are quite common for fine-grained surfaces (Lyot, 1929;Shkuratov et al., 1992Shkuratov et al., , 1994Shkuratov et al., 2002;Shkuratov et al., 2004;Levasseur-Regourd et al., 2015;Ovcharenko et al., 2006;Muinonen et al., 2015). The IS is caused by the shadowing effect, if constituent particles or their aggregates are absorbing, and, partially, by coherent backscattering enhancement (e.g., Shkuratov et al., 2011;Hapke, 2012). ...
We model negative polarization, which is observed for planetary regoliths at backscattering, solving a full wave problem of light scattering with a numerically exact Discontinuous Galerkin Time Domain (DGTD) method. Pieces of layers with the bulk packing density of particles close to 0.5 are used. The model particles are highly absorbing and have irregular shapes and sizes larger than the wavelength of light. This represents a realistic analog of low-albedo planetary regoliths. Our simulations confirm coherent backscattering mechanism of the origin of negative polarization. We show that angular profiles of polarization are stabilized if the number of particles in a layer piece becomes larger than ten. This allows application of our approach to the negative polarization modeling for planetary regoliths.
... Optical opposition phenomena like intensity surge (IS), i.e. nonlinear enhancement of intensity, and negative polarization (NP) (e.g., [11][12][13] ) of light scattered at large scattering angles are often ob- * Corresponding author. ...
We numerically simulate multiple light scattering in discrete disordered media represented by large clusters of irregular non-absorbing particles. The packing density of clusters is 0.5. With such conditions diffuse scattering is significantly reduced and light transport follows propagation channels that are determined by the particle size and topology of the medium. This kind of localization produces coherent backscattering intensity surge and enhanced negative polarization branch if compared to lower density samples.
... It should be emphasized that the albedo map inFig. 1 does present real brightness distribution at a¼0, as it ignores variations of opposition-effect amplitudes that are not described by formula (7). The opposition spike has components of shadow-hiding and coherent backscattering effects (e.g., Hapke, 1993; Shkuratov et al., 2004). To include these in the analysis, a more complicated approximation of the phase function is needed (Velikodsky et al., 2010).Fig. 2 shows a distribution of the longitudinal component r l of the topographic slope calculated on a 3.2 km base. ...
Lunar images acquired at non-zero phase angles show brightness variations caused by both albedo heterogeneities and local topographic slopes of the surface. To distinguish between these two factors, altimetry measurements or photoclinometry data can be used. The distinction is especially important for imagery of phase-function parameters of the Moon. The imagery is a new tool that can be used to study structural anomalies of the lunar surface. To illustrate the removal of the topographic effects from photometric images, we used Earth-based telescopic observations, altimetry measurements carried out with the Kaguya (JAXA) LALT instrument, and a new photoclinometry technique that includes analysis of several images of the same scenes acquired at different phase angles. Using this technique we have mapped the longitudinal component of lunar topography slopes (the component measured along the lines of constant latitude). We have found good correlations when comparing our map with the corresponding data from Kaguya altimetry. The removal of the topographic surface properties allows for the study of the phase-function parameters of the lunar surface, not only for flat mare regions, but for highlands as well.
... For atmosphereless bodies in the solar system, two light-scattering phenomena are observed near the opposition: the opposition effect and the negative polarization extending to some 201 from the exact backscattering direction, e.g. [1][2][3][4][5][6][7]. There have been many attempts to explain the negative polarization from the day it was discovered for the Moon by Lyot [8]. ...
We investigate the single-scattering interference mechanism related to the negative polarization branch (NPB) and intensity enhancement branch (IEB) near the backscattering direction for wavelength-scale Gaussian-random-sphere particles. Previously, we showed that for wavelength-scale spherical particles there is a two-part mechanism related to the longitudinal and the transverse components of the internal electric fields that are responsible for producing both the NPB and IEB near the backscattering direction. For comparison with the previous study, we have chosen the ensemble-averaged parameters of the Gaussian-random-sphere particles to be equivalent to those for spherical particles. We conclude that the same mechanism also can explain the NPB and IEB for non-spherical particles and that the mechanism seems to be stronger inside spherical particles, mainly because of stronger interference, and becomes weaker as the particle becomes more non-spherical.
... This note is motivated in response to the paper by Petrova et al. (2007) which considered different physical mechanisms of negative polarization of light scattered by aggregated aerosol particles. Studies of such mechanisms are important for developing remote sensing polarimetric techniques (e.g., Shkuratov et al., 2004). One of them considers a so-called "near-field effect" and potentially can explain the wide-phase-angle branch of negative polarization observed for cometary comas and planetary regoliths (Tishkovets, 1998;Petrova et al., 2007). ...
We show that the mechanism called “near-field effect” [e.g., Petrova, E.V., Tishkovets, V.P., Jockers, K., 2007. Icarus 188, 233–245], which is used to explain wide-phase-angle negative polarization branch observed for planetary regoliths and cometary comas, is not realistic as it contradicts laboratory experiments and results of modeling with discrete dipole approximation calculations.
... Enceladus' brightness surge confirms the measurements reported by Verbiscer et al. (2005) Smaller values of Enceladus' phase coefficients in comparison with those of Tethys and Rhea are somewhat surprising. Coherent backscattering models predict an increase of a phase curve slope with albedo growth (Shkuratov et al., 2004). Although the constructive wave interference is thought to be the main contributor to the backscattering peak of intensity of high albedo surfaces, the opposition spike of Enceladus is not as steep as might be expected considering the moon's high albedo. ...
Photopolarimetric observations of Saturn's satellites Enceladus, Tethys, Dione, and Rhea were obtained with the 2 m RCC telescope at the National Astronomical Observatory, Rozhen, in two different phase-angle regions (from 0.07° to 0.01° and from 5.6° to 5.2°). In this paper we present the first results of disk-integrated satellite photometry including mutually consistent solar and rotational phase curves in the red and near infrared bands (λ=694 and 889 nm). Enceladus, Tethys, Dione, and Rhea demonstrate a sharp brightness increase in the narrow backscattering domain of the phase angles (between 0.7° and 0.01°) revealing presence of a narrow component of the brightness opposition effect. The slopes of the low phase-angle portions of the moons’ phase curves are about 0.2 mag/deg, that is at the level of or even exceeds the slope of Europa's phase curve at opposition. The amplitudes of the moons’ opposition effects, measured by the total increase in the brightness as the phase angle decreased from 5° to 0°, are largely consistent with contribution of the coherent backscattering, which originated from the fraction of scatterers with sizes comparable to the wavelength of incident radiation. At the same time, the dependence of the relative strength of the moons’ brightening on their albedos, which become noticeable at the near infrared, points out that a shadow hiding component can also contribute to the opposition effects of these icy moons. The satellites’ rotation curves confirm that the leading/training albedo asymmetry known from previous visual observations extends into red and near infrared. The amplitudes of hemispherical asymmetries in the red and near infrared are quite similar and amount to 4%, 8%, 38%, and 18% for Enceladus, Tethys, Dione and Rhea, respectively.
... Negative polarization is a peculiar case of partially linearly polarized scattered light where the electric field vector component parallel to the scattering plane predominates over the perpendicular component. Observations of the abovementioned opposition phenomena for various kinds of solar system bodies have a long history, whereas the understanding of their physical nature has progressed considerably only during the last two decades (for reviews, see, e.g., Muinonen et al., 2002;Shkuratov et al., 2004). There are several physical mechanisms that may contribute to the opposition phenomena depending on the properties of the surfaces. ...
Physical properties of Kuiper belt objects (KBOs) can be assessed by studying their photometric and polarimetric phase effects close to opposition, i.e., the brightness opposition effect and the negative polarization branch. The first phase-curve observations and their promising preliminary interpretations are reviewed for KBOs and Centaurs. Despite the limited range of phase angles accessible from groundbased observations, distinct features have been discovered both in brightness and polarization. Recent results of relevant numerical and laboratory simulations of phase-angle effects are reviewed. The possibility of constraining the geometric albedos of the surfaces based on photometric and polarimetric observations is discussed.
... Laboratory measurements of powder samples show that such observable parameters as the half-width of the brightness opposition peak, the inversion angle of polarization α inv and the minimum value of the negative polarization |P min | strongly depend on the physical properties of particles and structure of the surface. A detailed analysis of the observational data near opposition can be found in a recent review [64]. ...
... Integral phase functions of intensity and polarization for the Moon[64]. ...
Measurements of light scattered from particulate surfaces provide information about the composition and structure of the surfaces.
An obvious way to characterize the scattering properties is to consider how the brightness and polarization of scattering
depend on the wavelength λ of incident light and the geometry of observations. The geometry is often characterized by the
phase angle α which is defined as the source-object-detector angle. Instead of α the scattering angle θ = π − α is used also.
The plane defined by the light source, scattering object and detector is called the scattering plane. The method of optical
remote sensing of particulate surfaces is based on the measurements of the characteristics as functions of λ and α. The problem
of theoretical interpretation of this kind of data is not solved at present. Numerical modeling based on the geometric optics
(GO) approximation can be efficient for some practical applications. In chapter we give an introduction to the past and current
status of the theoretical methods and GO simulation results achieved for media consisting of particles large compared to the
wavelength of incident light.
... Upon scattering the radiation becomes polarized and the polarization degree P varies with the phase angle α. In particular at small phase angles the wide negative polarization branch with |P min | ≈ 1 %, α min ≈ 11°, and inversion angle equal 22° is observed [1][2][3] I are intensities measured, respectively, at parallel and perpendicular orientations of the analyzer axis with respect to the scattering plane). The negative polarization is observed for different particulate surfaces, an example of which is the lunar regolith. ...
... we know that the wide negative polarization branch values of |P min | is a function of particulate surface albedo and particle size [3,8,9]. The brighter the particulate surface, the higher, the incoherent multiple scattering, hence, the lower |P min | should be. ...
At small phase angles the Moon reveals a wide negative polarization branch whose inversion angle is 22° and whose average amplitude is 1%. We present results of polarimetric mappings of the Moon in Pmin at a phase angle near 11°. The observations in the red and blue spectral bands were carried out with the Kharkov 50-cm telescope at the Maidanak Observatory (Middle Asia) using a Canon-350D camera and polarizing filter. A thorough calibration of the camera array (flat field and so on) allows for the reliable detection of significant variations of |Pmin| over the lunar surface, from 0.2 to 1.6 %. Smallest |Pmin| are characteristic of young bright craters; the parameter |Pmin| is the highest for the lunar highland and bright mare areas.
