Dr. Chao Wang Profile

Dr. Chao Wang

at Tongji Univ

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Proceedings Article | 27 June 2023 Paper

A comparative study on continuum removal for Chang’E-4 VNIS hyperspectral data and its impact on elements retrieval

Chao Wang, Xiangsui Zeng, Jia Li, Liyan Shang, Jiong Feng

Proceedings Volume 12705, 127052Y (2023) https://doi.org/10.1117/12.2680038

KEYWORDS: Absorption, Minerals, Short wave infrared radiation, Reflectivity, Visible radiation, Near infrared, Spectroscopy, Light absorption

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Spectral absorption features are important parameters for lunar mineral identification and its abundance retrieval. The spectral absorption features of lunar regolith around 1000 nm (Band I) and 2000 nm (Band II) are significant weakened due to long-history space weathering. Continuum removal can effectively enhance the features of spectral absorption for lunar surface materials, which is particularly applicable for processing the in-situ hyperspectral data that obtained by the Visible and Near Infrared Spectrometer (VNIS) onboard Chang’E-4 Yutu-2 Rover that landed in Von Kármán crater. In this paper, three types of functions, i.e., linear, the second-order parabola polynomial and the piecewise polynomial functions, are used to fit the continuum of VNIS spectra, and further accessing their influences on calculating the parameters of spectral absorption features. The study shows that the piecewise polynomial continuum performs the best in enhancing the spectral absorption features of VNIS data in Bands I and II. Both endpoints of the continuum can be found. The derived absorption features, such as band depth and centers are highly consistent with those obtained with ENVI software, who uses the full convex hull to determine spectral continuum. The difference between the piecewise polynomial method and full convex hull method in absorption band center and band area ratio is less than 1%. In addition, we tested the retrieval of Wo and Fs with the spectral feature parameters from different continuums and find that continuum composed by piecewise linear equation is appropriate.

Proceedings Article | 27 January 2021 Paper

A novel method for inversing FeO content from spectral absorption characteristics and maturity index using LSCC data

Liyan Shang, Chao Wang, Shijie Liu

Proceedings Volume 11720, 117202D (2021) https://doi.org/10.1117/12.2589329

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Iron is one of the major elements on the Moon. In general, it exists in two forms, i.e. FeO and submicroscopic metallic iron (SMFe). The presence of FeO on the Moon is of great significance in studying the history of lunar lava differentiation and its evolution. However, it has been difficult to inverse the abundance of FeO from the spectral data of the Moon, since the two forms of iron have opposite optical effects on the spectral absorption characteristics of the lunar surface. The spectral absorption depth will be strengthened by FeO, while weakened by SMFe that is produced by space weathering. The FeO of the Moon is inversed either directly from reflectance spectra or spectral absorption characteristics of satellite, telescope and in-situ obtained spectra, both without taking into account the effect of space weathering, which may induce bias on the FeO inverse. The degree of space weathering can be expressed by various maturity indexes, such as magnetic maturity (e.g. Is and Is/FeO) and optical maturity (e.g. OMAT and continuum slope). To better quantitate the content of FeO from the lunar spectra, in this study, we first investigate the variations of spectral absorption depth and maturity indexes due to different degrees of space weathering using Hapke radiative transfer model. Then the correlation of different maturity indexes is analyzed. Based on these, to consider the optical effects of FeO and SMFe, a novel method to inverse the FeO from lunar spectra are established. By comparing the FeO derived with the new method with four methods proposed by others, the FeO derived in this study yields a better correlation with laboratory measured FeO contents using LSCC data.

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