Applications of AOTF Spectrometers in In Situ Lunar Measurements

Spectrometers based on acousto-optic tunable filters (AOTFs) have several advantages, such as stable temperature adaptability, no moving parts, and wavelength selection through electrical modulation, compared with the traditional grating and Fourier transform spectrometers. Therefore, AOTF spectrometers can realize stable in situ measurement on the lunar surface under wide temperature ranges and low light environments. AOTF imaging spectrometers were first employed for in situ measurement of the lunar surface in the Chinese Chang’e project. The visible and near-infrared imaging spectrometer and the lunar mineralogical spectrometer have been successfully deployed on board the Chang’e-3/4 and Chang’e-5 missions. In this review, we investigate the performance indicators, structural design, selected AOTF performance parameters, data acquisition of the three lunar in situ spectral instruments used in the Chang’e missions. In addition, we also show the scientific achievement of lunar technology based on in situ spectral data.

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Effect of Lunar Complex Illumination on In Situ Measurements Obtained Using Visible and Near-Infrared Imaging Spectrometer of Chang’E-4

Remote Sensing ◽

10.3390/rs13122359 ◽

2021 ◽

Vol 13 (12) ◽

pp. 2359

Author(s):

Jiafei Xu ◽

Meizhu Wang ◽

Rong Wang ◽

Qi Feng ◽

Honglei Lin ◽

...

Keyword(s):

Lunar Surface ◽

Near Infrared ◽

Infrared Imaging ◽

Specular Reflection ◽

In Situ Measurements ◽

The Moon ◽

Spectral Measurements ◽

Near Infrared Imaging ◽

Imaging Spectrometer

In-situ measurements of the spectral information on the lunar surface are of significance to study the geological evolution of the Moon. China’s Chang’E-4 (CE-4) Yutu-2 rover has conducted several in-situ spectral explorations on the Moon. The visible and near-infrared imaging spectrometer (VNIS) onboard the rover has acquired a series of in-situ spectra of the regolith at the landing site. In general, the mineralogical research of the lunar surface relies on the accuracy of the in-situ data. However, the spectral measurements of the Yutu-2 rover may be affected by shadows and stray illumination. In this study, we analyzed 106 CE-4 VNIS spectra acquired in the first 24 lunar days of the mission and noted that six of these spectra were affected by the shadows of the rover. Therefore, a method was established to correct the effects of the rover shadow on the spectral measurements. After shadow correction, the FeO content in the affected area is corrected to 14.46 wt.%, which was similar to the result calculated in the normal regolith. Furthermore, according to the visible images, certain areas of the explored sites were noted to be unusually bright. Considering the reflectance, geometric information, and shining patterns of the multi-layer insulation (MLI), we examined the influence of the specular reflection of the MLI on the bright spot regionsd , and found that the five sets of data were likely not affected by the specular reflection of the MLI. The results indicated that the complex illumination considerably influences the in situ spectral data. This study can provide a basis to analyze the VNIS scientific data and help enhance the accuracy of interpretation of the composition at CE-4 landing sites.

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Visible and near-infrared imaging spectrometer (VNIS) for in-situ lunar surface measurements

10.1117/12.2194526 ◽

2015 ◽

Cited By ~ 5

Author(s):

Zhiping He ◽

Rui Xu ◽

Chunlai Li ◽

Gang Lv ◽

Liyin Yuan ◽

...

Keyword(s):

Lunar Surface ◽

Near Infrared ◽

Infrared Imaging ◽

Near Infrared Imaging ◽

Imaging Spectrometer ◽

Surface Measurements

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Photometric Normalization of Chang’e-4 Visible and Near-Infrared Imaging Spectrometer Datasets: A Combined Study of In-Situ and Laboratory Spectral Measurements

Remote Sensing ◽

10.3390/rs12193211 ◽

2020 ◽

Vol 12 (19) ◽

pp. 3211

Author(s):

Xiaobin Qi ◽

Zongcheng Ling ◽

Jiang Zhang ◽

Jian Chen ◽

Haijun Cao ◽

...

Keyword(s):

Near Infrared ◽

Infrared Imaging ◽

Landing Site ◽

Near Infrared Imaging ◽

Imaging Spectrometer ◽

Quantitative Mineralogy ◽

Infrared Spectral ◽

Phase Functions ◽

Phase Angles

Until 29 May 2020, the Visible and Near-Infrared Imaging Spectrometer (VNIS) onboard the Yutu-2 Rover of the Chang’e-4 (CE-4) has acquired 96 high-resolution surface in-situ imaging spectra. These spectra were acquired under different illumination conditions, thus photometric normalization should be conducted to correct the introduced albedo differences before deriving the quantitative mineralogy for accurate geologic interpretations. In this study, a Lommel–Seeliger (LS) model and Hapke radiative transfer (Hapke) model were used and empirical phase functions of the LS model were derived. The values of these derived phase functions exhibit declining trends with the increase in phase angles and the opposition effect and phase reddening effect were observed. Then, we discovered from in-situ and laboratory measurements that the shadows caused by surface roughness have significant impacts on reflectance spectra and proper corrections were introduced. The validations of different phase functions showed that the maximum discrepancy at 1500 nm of spectra corrected by the LS model was less (~3.7%) than that by the Hapke model (~7.4%). This is the first time that empirical phase functions have been derived for a wavelength from 450 to 2395 nm using in-situ visible and near-infrared spectral datasets. Generally, photometrically normalized spectra exhibit smaller spectral slopes, lower FeO contents and larger optical maturity parameter (OMAT) than spectra without correction. In addition, the band centers of the 1 and 2 μm absorption features of spectra after photometric normalization exhibit a more concentrated distribution, indicating the compositional homogeneity of soils at the CE-4 landing site.

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Control and on-Board Calibration Method for in-Situ Detection Using the Visible and Near-Infrared Imaging Spectrometer on the Yutu-2 Rover

Image and Graphics Technologies and Applications - Communications in Computer and Information Science ◽

10.1007/978-981-33-6033-4_20 ◽

2020 ◽

pp. 267-281

Author(s):

Jia Wang ◽

Tianyi Yu ◽

Kaichang Di ◽

Sheng Gou ◽

Man Peng ◽

...

Keyword(s):

Near Infrared ◽

Infrared Imaging ◽

Calibration Method ◽

Near Infrared Imaging ◽

Imaging Spectrometer ◽

In Situ Detection

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In-Situ Calibration of Relative Reflectance for Visible/Near-Infrared Imaging Spectrometer

Sensor Letters ◽

10.1166/sl.2012.1845 ◽

2012 ◽

Vol 10 (1) ◽

pp. 198-204

Author(s):

Dongyan Zhang ◽

Guijun Yang ◽

Xiaoyu Song ◽

Zhijie Wang ◽

Dacheng Wang ◽

...

Keyword(s):

Near Infrared ◽

Infrared Imaging ◽

Near Infrared Imaging ◽

Imaging Spectrometer ◽

In Situ Calibration

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Estimation of Noise in the In Situ Hyperspectral Data Acquired by Chang’E-4 and Its Effects on Spectral Analysis of Regolith

Remote Sensing ◽

10.3390/rs12101603 ◽

2020 ◽

Vol 12 (10) ◽

pp. 1603

Author(s):

Honglei Lin ◽

Yangting Lin ◽

Yong Wei ◽

Rui Xu ◽

Yang Liu ◽

...

Keyword(s):

Spectral Analysis ◽

Lunar Surface ◽

Near Infrared ◽

Infrared Imaging ◽

Hyperspectral Data ◽

Repeated Measurements ◽

Imaging Spectrometer ◽

Low Snr ◽

Spectral Interpretation ◽

Geologic Interpretation

The Chang’E-4 (CE-4) spacecraft landed successfully on the far side of the Moon on 3 January 2019, and the rover Yutu-2 has explored the lunar surface since then. The visible and near-infrared imaging spectrometer (VNIS) onboard the rover has acquired numerous spectra, providing unprecedented insight into the composition of the lunar surface. However, the noise in these spectral data and its effects on spectral interpretation are not yet assessed. Here we analyzed repeated measurements over the same area at the lunar surface to estimate the signal–noise ratio (SNR) of the VNIS spectra. Using the results, we assessed the effects of noise on the estimation of band centers, band depths, FeO content, optical maturity (OMAT), mineral abundances, and submicroscopic metallic iron (SMFe). The data observed at solar altitudes <20° exhibit low SNR (25 dB), whereas the data acquired at 20°–35° exhibit higher SNR (35–37 dB). We found differences in band centers due to noise to be ~6.2 and up to 28.6 nm for 1 and 2 μm absorption, respectively. We also found that mineral abundances derived using the Hapke model are affected by noise, with maximum standard deviations of 6.3%, 2.4%, and 7.0% for plagioclase, pyroxene, and olivine, respectively. Our results suggest that noise has significant impacts on the CE-4 spectra, which should be considered in the spectral analysis and geologic interpretation of lunar exploration data.

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