During its first two lunar day measurements, the visible and near‐infrared spectrometer on board the Yutu‐2 Rover of the Chang'E‐4 mission acquired six in situ reflectance spectra from the floor of Von Kármán crater within the South Pole‐Aitken basin. A spectral lookup table search has shown that the regolith at the landing site contains 56–72% plagioclase, 9–28% orthopyroxene, 4–19% clinopyroxene, and 2–12% olivine, in relative abundance, in agreement with the results from Kaguya Multiband Imager mineral mapping. A mineral composition analysis using measurements made by the Moon Mineralogy Mapper and the Multiband Imager has shown that the surface materials of the landing site may have been ejected from the nearby Finsen crater. This result is also supported by principal component analysis which shows a strong correlation between the compositions of the landing area and Finsen crater.
Context. The Yutu-2 rover of the Chang’E-4 (CE-4) mission measured the lunar phase curves in the Von Kármán crater, South Pole-Aitken basin.
Aims. We aim to study the photometric properties of the regolith at CE-4’s landing site and compare them with those of Chang’E-3 (CE-3) in order to understand the regolith physical properties of the two landing sites.
Methods. We extracted the insitu lunar phase curves measured by CE-4 with a very wide phase angle coverage (1°–144°) and performed photometric model inversions using both the Hapke model and the Lumme-Bowell model.
Results. Compared with the CE-3 measurement taken in Mare Imbrium, the CE-4 phase curves show the colorimetric opposition effect and have a steeper and narrower opposition spike. The surface regolith at the CE-4 site is much darker, more porous, more forward scattering, and has a larger slope angle (Hapke model) than that of CE-3.
Conclusions. The CE-4 site may have experienced more space weathering alterations than the CE-3 site, which is consistent with their different surface model ages (~3.6 Ga for CE-4 and ~3 Ga for CE-3).
We present a modulation transfer spectroscopy (MTS) configuration based on an acousto-optic modulator by using a variant of the typical double pass structure. One beam is modulated by using an acousto-optic modulator in opposite diffraction order to cancel the carrier frequency shift and produce a modulated pump beam. The line shape performance is investigated theoretically and experimentally. Laser frequency stabilization of the proposed configuration is demonstrated for the 133 Cs |6 2 S 1/2 , F = 4 → |6 2 P 3/2 , F = 5 transition. The Allan deviations, which are measured by using beat note signals and the three-cornered hat method, are 3.6×10 −11 in an integration time of 100 s and approximately 4×10 −11 in a longer integration time.
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