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71.
Kohei Kitazato Beth E. Clark Shinsuke Abe Takahiro Hiroi Paul A. Abell Faith Vilas 《Icarus》2008,194(1):137-145
A photometric analysis of the S-type Asteroid 25143 Itokawa is performed over multiple wavelengths ranging from 0.85 to 2.10 μm based on disk-resolved reflectance spectra obtained with the Hayabusa near-infrared spectrometer (NIRS). We derive the global photometric properties of Itokawa in terms of Hapke's photometric model. We find that Itokawa has a single-scatter albedo that is 35-40% less than that of Asteroid 433 Eros. Itokawa also has a single-particle phase function that is more strongly back-scattering than that of Eros. Despite its hummocky surface strewn with large boulders, Itokawa exhibits an opposition effect. However, the total amplitude of the opposition surge for Itokawa was estimated to be less than unity while Eros and other S-type asteroids have been found to have model values exceeding unity. The wavelength dependence of the opposition surge width reveals that coherent backscatter contributes to the opposition effect on Itokawa's surface. The photometric roughness of Itokawa is well constrained to a value of 26° ± 1° which is similar to Eros, suggesting that photometric roughness models the smallest surface roughness scale for which shadows exist. 相似文献
72.
Elvira Bura-Naki Eric Viollier Didier Jzquel Alassane Thiam Irena Ciglene
ki 《Chemical Geology》2009,266(3-4):320-326
The vertical distribution of reduced sulfur species (RSS including H2S/HS−, S0, electroactive FeS) and dissolved Fe(II) was studied in the anoxic water column of meromictic Lake Pavin. Sulfide concentrations were determined by two different analytical techniques, i.e. spectophotometry (methylene blue technique) and voltammetry (HMDE electrode). Total sulfide concentrations determined with methylene blue method (∑H2SMBRS) were in the range from 0.6 µM to 16.7 µM and were substantially higher than total reduced sulfur species (RSSV) concentrations determined by voltammetry, which ranged from 0.1 to 5.6 μM. The observed difference in the sulfide concentrations between the two methods can be assigned to the presence of FeS colloidal species.Dissolved Fe was high (> 1000 µM), whereas dissolved Mn was only 25 µM, in the anoxic water column. This indicates that Fe is the dominant metal involved in sulfur redox cycling and precipitation. Consequently, in the anoxic deep layer of Lake Pavin, “free” sulfide, H2S/HS−, was low; and about 80% of total sulfide detected was in the electroactive FeS colloidal form. IAP calculations showed that the Lake Pavin water column is saturated with respect to FeSam phase. The upper part of monimolimnion layer is characterized by higher concentrations of S(0) (up to 3.4 µM) in comparison to the bottom of the lake. This behavior is probably influenced by sulfide oxidation with Fe(III) oxyhydroxide species. 相似文献
73.
74.
Y. Shkuratov V. Kaydash V. Korokhin Y. Velikodsky N. Opanasenko G. Videen 《Planetary and Space Science》2011,59(13):1326-1371
This survey is a general overview of modern optical studies of the Moon and their diagnostic meaning. It includes three united parts: phase photometry, spectrophotometry, and polarimetry. The first one is devoted to the progress in the photometry of the Moon, which includes absolute albedo determination to refine the albedo scale (e.g., to connect lunar observations and the data of lunar sample measurements) and mapping the parameters of a lunar photometric function (e.g., the phase-angle ratios method) with the aim of making qualitative estimates of regolith structure variations. This part also includes observations of the lunar opposition effect as well as photogrammetry and photoclinometry techniques. In particular, available data show that because of the low albedo of the lunar surface, the coherent backscattering enhancement hardly influences the lunar opposition spike, with the exception of the brightest lunar areas measured in the NIR. The second part is devoted to chemical/mineral mapping of the Moon's surface using spectrophotometric measurements. This section also includes analyses related to the detection of water ice or hydroxyl, prognoses of maturity, and helium-3 abundance mapping. In particular, we examine the relationship between superficial OH/H2O compounds spectrally detected recently and bulk “water ice” found earlier by the Lunar Prospector GRS and LRO LEND, assuming that the compounds are delivered to cold traps (permanently shadowed regions) with electrostatically levitated dust saturated by solar wind hydrogen. Significant problems arise with the determination of TiO2 content, as the correlation between this parameter and the color ratio C(750/415 nm) is very non-linear and not universal for different composition types of the lunar surface; a promising way to resolve this problem is to use color ratios in the UV spectral range. The third part is devoted to mapping of polarization parameters of the lunar surface, which enable estimates of the average size of regolith particles and their optical inhomogeneity. This includes considerations of the Umov effect and results of spectropolarimetry, negative polarization imagery, and measurements of other polarimetric parameters, including the third Stokes parameter. Although these three research divisions have not been developed equally and the numbers of proper references are very different, we try to keep a balance between them, depicting a uniform picture. It should be emphasized that many results presented in this review can be applied to other atmosphereless celestial bodies as well. 相似文献
75.
In conjunction with a companion paper (Shepard, M.K., Helfenstein, P. [2011]. Icarus, submitted for publication), we derive, test, and apply a detailed approach for visualizing the phase angle dependence of light scattering in particulate soils from both whole-disk and disk-resolved observations. To reduce the number of model parameters and provide stronger constraints on model fits, we combine Hapke’s (Hapke, B. [2008]. Icarus 195, 918-926) recent correction for effects of porosity with his (Hapke, B. [1986]. Icarus 67, 264-280) model of the shadow hiding opposition effect. We further develop our method as a tool for least-squares fitting of Hapke’s model to photometric data. Finally, we present an improved method for estimating uncertainties in retrieved values of Hapke model parameters. We perform a preliminary test of the model on spectrogoniometric measurements from three selected laboratory samples from Shepard and Helfenstein (Shepard, M.K., Helfenstein, P. [2007]. J. Geophys. Res. 112 (E03001), 17). Our preliminary suite of test samples is too small and selective to permit the drawing of general conclusions. However, our results suggest that Hapke’s porosity correction improves the fidelity of fits to samples composed of low- and moderate-albedo particles and may allow for more reliable retrieval of porosity estimates in these materials. However, we find preliminary evidence that in high-albedo surfaces, the effects of porosity may be difficult to detect. 相似文献
76.
本文介绍了在阳离子表面活性剂存在下锡[Sn(Ⅳ)]与邻氯苯基荧光酮(O-Cl-PF)胶束增溶显色反应的研究结果,发现在溴化十六烷基三甲基铵(CTMAB)存在下,Sn(Ⅳ)与O-Cl-PF可形成深颜色的络合物,其最大吸收在534nm处,络合物的摩尔吸收系数为1.83×10~5lmol~(-1)·cm~(-1)在0—8μgSn(Ⅳ)/25范围内符合比尔定律,采用等摩尔连续变换法确定了络合物的组成为Sn(Ⅳ):O-Cl-PF=1:4、本文提出了不经分离其伴生元素而快速测定铀矿石中微量Sn(Ⅳ)的新方法,所得结果令人满意。 相似文献
77.
对于总氮和总磷的测定,国家标准HJ636—2012和GB11893—89规定总氮用碱性过硫酸钾消解,紫外分光光度法测定,总磷用中性过硫酸钾消解,分光光度法测定,两种方法分别取样、消解,分析效率低。本文对国家标准方法进行改进,建立了在一份样品中用过硫酸钾作为氧化剂一次消解,分光光度法联合测定树干茎流液中总氮、总磷含量的方法。样品中的含氮化合物在碱性过硫酸钾溶液中,在高温下氧化分解转化为硝酸盐氮(NO-3-N),其吸光度与总氮浓度成正比;含磷化合物在酸性过硫酸钾溶液中,在高温下氧化分解转化成正磷酸盐(PO3-4-P),其吸光度与正磷酸盐浓度成正比。经实际样品验证,方法精密度(RSD,n=5)为总氮2%,总磷4%,加标回收率为98.0%~104.2%(总氮)和94.0%~107.0%(总磷)。本方法将国家标准方法中配制两条标准系列、两次高压消解改进为配制一条标准系列、一次消解,可以节省50%的样品使用量,且提高了分析效率。由于有机质含量较高时,在本法条件下样品不易消解清亮,影响总氮、总磷的测定,该方法适用于有机质含量较低的树干茎流样品分析。 相似文献
78.