The researchers made geometric corrections for the illumination of Yutu-2’s spectrum

Reflectance spectroscopy is the most important means to obtain the composition of the lunar surface, but there are many factors that affect the spectrum. In addition to the material composition, physical properties and degree of space weathering of the lunar surface, it is also affected by geometric factors during detection, including incident angle, emission angle and phase angle. Therefore, studying the influence of the geometric factors of illumination and correcting it is the premise to accurately invert the composition of the lunar surface material and the degree of space weathering. The study of the effect of different geometrical lighting conditions on the spectrum is usually carried out in the laboratory using simulated lunar soil or Apollo lunar samples. However, even if the real Apollo lunar soil sample is used, its surface is not in the original state when it was on the lunar surface, so the results measured under simulated conditions may be quite different from the real lunar surface. After the Apollo program, only Chang’e 3 and Chang’e 4 successfully landed on the lunar surface, and carried lunar rovers (Yutu 1 and 2) respectively to conduct in-situ measurements of the lunar soil with a visible-near-infrared imaging spectrometer. On January 3, 2019, Chang’e-4 landed on the Von Karman crater in the South Pole-Aiken Basin on the far side of the moon, and carried out a survey exploration (Fig. 1a), expecting to obtain the deep material composition of the moon. On the fourth lunar day after the landing of Chang’e-4, Yutu-2 conducted the first in-situ spectral measurement experiment on the lunar surface under different lighting geometric conditions (Fig. 1b).

The team of Lin Yangting, a researcher at the Institute of Geology and Geophysics, Chinese Academy of Sciences, used the spectrum measured by Yutu-2 on the fourth month day to deduce the lunar surface in-situ luminosity covering the visible-near-infrared band (470-945 nm, 5nm interval) for the first time. function, and using the photometric function to correct the spectrum to the standard observation angle (i.e. photometric correction), more accurate FeO content and maturity of the lunar soil were obtained.

Due to the exposure of the regolith in the landing zone for 3.6 billion years, the lunar soil has been uniformly mixed, which is consistent with the panorama taken by Yutu-2 (Figure 2). good place. The experiment was carried out by rotating the lunar rover at a certain angle in the center and performing spectral measurements on the surrounding lunar soil. The actual measured area diameter is less than 5 m, which can be considered as a homogeneous surface with a phase angle coverage of 39.6°–97.1° (Fig. 1b). Through data analysis, it is found that there is a good correlation between the phase function and the phase angle (Fig. 3a), and it varies with wavelength (Fig. 3b); the correction coefficient from a specific phase angle to a phase angle of 30 degrees decreases with increasing wavelength small (Fig. 3c); for each wavelength of reflectivity, the larger the phase angle, the larger the correction factor corrected to a phase angle of 30 degrees.

The spectra were corrected to standard geometric angles (incidence angle 30°, exit angle 0°, phase angle 3°) using the derived photometric function, and the FeO content and optical maturity (OMAT) of the lunar soil were calculated using the corrected spectra. ). The reflectance spectrum without photometric function correction shows significant dispersion for the inversion of FeO content and OMAT in lunar soil in a small area (diameter

The research results were published in JGR-Planets.

The researchers made geometric corrections for the illumination of Yutu-2’s spectrum

Figure 1 (a) The driving route of the Yutu-2 lunar rover in the first April day; (b) The schematic diagram of the spectral measurement experiment with different lighting geometric conditions

Figure 2 Panoramic photo of the experimental area

Fig. 3 Lunar phase function of Chang’e-4 landing site. (a) Fitting of the phase function at 500 nm and 750 nm, f(α) is the phase function; (b) the phase function at 470-945 nm; (c) the comparison of the phase function between different wavelengths; (d) normalization Phase function to 750 nm

Reflectance spectroscopy is the most important means to obtain the composition of the lunar surface, but there are many factors that affect the spectrum. In addition to the material composition, physical properties and degree of space weathering of the lunar surface, it is also affected by geometric factors during detection, including incident angle, emission angle and phase angle. Therefore, studying the influence of the geometric factors of illumination and correcting it is the premise to accurately invert the composition of the lunar surface material and the degree of space weathering. The study of the effect of different geometrical lighting conditions on the spectrum is usually carried out in the laboratory using simulated lunar soil or Apollo lunar samples. However, even if the real Apollo lunar soil sample is used, its surface is not in the original state when it was on the lunar surface, so the results measured under simulated conditions may be quite different from the real lunar surface. After the Apollo program, only Chang’e 3 and Chang’e 4 successfully landed on the lunar surface, and carried lunar rovers (Yutu 1 and 2) respectively to conduct in-situ measurements of the lunar soil with a visible-near-infrared imaging spectrometer. On January 3, 2019, Chang’e-4 landed on the Von Karman crater in the South Pole-Aiken Basin on the far side of the moon, and carried out a survey exploration (Fig. 1a), expecting to obtain the deep material composition of the moon. On the fourth lunar day after the landing of Chang’e-4, Yutu-2 conducted the first in-situ spectral measurement experiment on the lunar surface under different lighting geometric conditions (Fig. 1b).

The team of Lin Yangting, a researcher at the Institute of Geology and Geophysics, Chinese Academy of Sciences, used the spectrum measured by Yutu-2 on the fourth month day to deduce the lunar surface in-situ luminosity covering the visible-near-infrared band (470-945 nm, 5nm interval) for the first time. function, and using the photometric function to correct the spectrum to the standard observation angle (i.e. photometric correction), more accurate FeO content and maturity of the lunar soil were obtained.

Due to the exposure of the regolith in the landing zone for 3.6 billion years, the lunar soil has been uniformly mixed, which is consistent with the panorama taken by Yutu-2 (Figure 2). good place. The experiment was carried out by rotating the lunar rover at a certain angle in the center and performing spectral measurements on the surrounding lunar soil. The actual measured area diameter is less than 5 m, which can be considered as a homogeneous surface with a phase angle coverage of 39.6°–97.1° (Fig. 1b). Through data analysis, it is found that there is a good correlation between the phase function and the phase angle (Fig. 3a), and it varies with wavelength (Fig. 3b); the correction coefficient from a specific phase angle to a phase angle of 30 degrees decreases with increasing wavelength small (Fig. 3c); for each wavelength of reflectivity, the larger the phase angle, the larger the correction factor corrected to a phase angle of 30 degrees.

The spectra were corrected to standard geometric angles (incidence angle 30°, exit angle 0°, phase angle 3°) using the derived photometric function, and the FeO content and optical maturity (OMAT) of the lunar soil were calculated using the corrected spectra. ). The reflectance spectrum without photometric function correction shows significant dispersion for the inversion of FeO content and OMAT in lunar soil in a small area (diameter

The research results were published in JGR-Planets.

Figure 1 (a) The driving route of the Yutu-2 lunar rover in the first April day; (b) The schematic diagram of the spectral measurement experiment with different lighting geometric conditions

Figure 2 Panoramic photo of the experimental area

Fig. 3 Lunar phase function of Chang’e-4 landing site. (a) Fitting of the phase function at 500 nm and 750 nm, f(α) is the phase function; (b) the phase function at 470-945 nm; (c) the comparison of the phase function between different wavelengths; (d) normalization Phase function to 750 nm

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