Photometric properties of lunar terrains derived from Hapke's equation

Hapke's bidirectional reflectance equations provide the most rigorous available description of photometric behavior in terms of physically meaningful parameters. The primary objective of this study was to derive Hapke parameters for the lunar surface from both disk-integrated and disk-resolved photometric data. Hapke's equation was fit to the disk-integrated phase curves and disk-resolved data for dark, average, and bright terrain classes using an iterative, nonlinear least squares algorithm described by Helfenstein. Parameters were initially determined from the disk-integrated data, and the result was applied as a first guess to the iterative solution of parameters for individual terrain classes. Plots are presented of the disk-resolved data normalized to corresponding brightnesses predicted from the disk-integrated solution under the same illumination and viewing geometries. Systematic trends in disk-resolved parameters can be identified. Values for single scattering albedo (w) of the dominantly anorthositic average and bright terrains are significantly larger than the value for the basaltic dark terrains (mare). Values for surge brightness parameters, particle phase function, and average topographic slope angle are also discussed

Study of the Effects of Photometric Geometry on Spectral Reflectance Measurements

The objective of this research is to investigate how the spectrophotometric properties of planetary surface materials depend on photometric geometry by refining and applying radiative transfer theory to data obtained from spacecraft and telescope observations of planetary surfaces, studies of laboratory analogs, and computer simulations. The goal is to perfect the physical interpretation of photometric parameters in the context of planetary surface geological properties and processes. The purpose of this report is to document the research achievements associated with this study

Anomalous scattering of light on Triton

Researchers report here the discovery of an isolated region of anomalously forward scattering materials on the surface of Triton. The researchers' best-fit Hapke parameters indicate that regolith particles in the anomalous scattering region are not only less backward scattering, but also slightly lower in single scattering albedo than average materials on Triton's surface. While it might be possible to account for such differences in terms of differences in particle size and transparency, it is also possible that the anomalous region is compositionally distinct from other terrains. It is noteworthy that, for the anomalous region, there exists a distinctively strong spatial correlation between the photometric ratios at different phase angles, and that, relative to other terrains, the anomalous region reddens at a different rate with increasing phase angle

Enceladus: Evidence for librations forced by Dione

Based on control point calculations it is shown that Enceladus experiences librations forced by Dione

Vis-NIR disk-integrated photometry of asteroid 25143 Itokawa around opposition by AMICA/Hayabusa

We present photometry of the S-type near-Earth asteroid 25143 Itokawa based on both ground-based observations in the UBVRI bands and measurements from the AMICA/Hayabusa spacecraft observations with ul-, b-, v-, w-, x-, and p-filters. Hayabusa observed Itokawa around opposition during the rendezvous, thus providing a unique set of observations of this asteroid. We fit the phase curve measurements with both the Classic Hapke Model (Hapke, 1981, 1984, 1986) and Modern Hapke Model (Hapke, 2002, 2008, 2012a) and thereby extract the physical properties of Itokawa's surface regolith. The single-scattering albedo (0.57 ± 0.05) is larger than that derived for Eros (0.43 ± 0.02), another S-type near-Earth asteroid visited by a spacecraft. Both models indicate a regolith that is forward-scattering in nature. From the hockey stick relationship derived for the single-particle phase function (Hapke, 2012b), both modeling results suggest a regolith comprised of rough surfaced particles with a low density of internal scatterers. Application of the Modern Hapke model derives porosity parameter values from 1 to 1.1, for BVR bands, which corresponds to porosity values between 77–79%. This suggests the surface of Itokawa is very fluffy and the large boulders may be bonded with smaller size particles, typical of the particle sizes observed in Muses Sea. Both models also provide similar geometric albedo values (0.27 ± 0.02) at the V-band wavelength, which are equivalent to Eros’ geometric albedo

The role of oxidative stress and antioxidant supplementation in pregnancy disorders

Oxidative stress is widely implicated in failed reproductive performance including infertility, miscarriage, diabetes-related congenital malformations and preeclampsia. Maternal obesity is a strong risk factor for preeclampsia, and recently, in an animal model of maternal obesity we have reported evidence of oxidative stress in the oocytes of obese animals prior to pregnancy as well as in early stage embryos. This adds to the growing evidence for a greater focus on the pre-conceptual period in prevention of pregnancy disorders including those related to oxidative stress. Our research has also focussed on the role of free radicals and antioxidant capacity in preeclampsia. Assessment by measurement of markers of lipid peroxidation or of antioxidant capacity has provided unequivocal evidence for oxidative stress in this disorder. Partial failure of the process of placentation has been implicated, with recent evidence proposing that ischaemia-reperfusion in the placenta may contribute to oxidative stress in trophoblast. Endoplasmic reticulum stress in the placenta may also play a role. We and others have performed randomised controlled trials to determine whether early supplementation with vitamins C and E in women at risk of preeclampsia may be beneficial but these studies have shown no evidence for prevention of preeclampsia. Whether this represents an inappropriate antioxidant strategy or whether supplementation has been too late in gestation to be beneficial is not known. Other potential approaches to prevention of preeclampsia through amelioration of oxidative stress include provision of supplements in the pre-conceptual period, selenium supplements, anti-peroxynitrite strategies and statins

Phase Curves from the Kuiper Belt: Photometric Properties of Distant Kuiper Belt Objects Observed by New Horizons

n/