Mineralogical mapping of selected areas of the lunar surface using Moon Mineralogy Mapper data.
von Yehor Surkov
Datum der mündl. Prüfung:2022-12-01
Betreuer:Prof. Dr. Martin Kappas
Gutachter:Dr. Urs Mall
Gutachter:Dr. Vadym Kaydash
EnglischThe dissertation is concerned with spectrophotometric studies of selected areas of the lunar surface using the data generated by the mapping spectrometer Moon Mineralogy Mapper (M3), onboard the Chandrayaan-1 spacecraft. Spectrophotometry is one tool to investigate planetary surfaces by remote sensing. This technique is based on the measurement and further interpretation of diffuse reflection spectra, which contain information about the chemical and mineralogical composition, as well as the structure of the regolith of the surfaces studied. The M3 spectrometer provided hyperspectral images covering 95 % of the lunar surface in the visible and near-infrared wavelengths range (from 540 to 3000 nm) with a spatial resolution of about 140 m/pixel. Unfortunately, due to the thermal issues during the flight, the Chandrayaan-1 spacecraft was not able to provide the M3 instrument the required stable environmental conditions for acquiring its data. This circumstance led to a deterioration of the data quality of the M3 instrument manifesting itself in various artifacts most visible in a random system of long, narrow vertical stripes which can be found on nearly all its hyperspectral images. This thesis proposes a new method to reduce the above-mentioned artifacts leading to a significant recovery of the original data quality. The new method consists of two stages: (1) a Gaussian convolution of the spectra recorded by an individual pixel of the image, and (2) a Fourier filtration of each spectral channel of the M3 image. These corrections are applied in an additional data processing step to the fully calibrated data which are publicly available through the Planetary Data System https://pds-imaging.jpl.nasa.gov/volumes/m3.html. With the help of the new approach it now becomes possible to clearly identify the spectral parameters which are needed to analyze the M3 reflectance spectra. The power of the new approach is demonstrated in this thesis by investigating the areas of the northwest portion of Aristarchus Plateau, Montes Agricola and contiguous maria. In particular, maps of the 1 and 2 μm absorption band positions were used to build Adam’s diagrams for the investigated regions. A cluster analysis of the diagram shows that the investigated area is composed of five spectral provinces which reveal significantly different mineralogic compositions mostly represented by pyroxenes of different types and lunar glasses. This approach has proved to be particularly useful for identifying and mapping the volcanic and pyroclastic glass deposits. It has been further applied to the investigation of pyroclastic glass on the southern part of Mare Vaporum. We could show that dark smooth deposits around a Hyginus crater contains pyroclastic material. They are the satellite pyroclastic deposits on this region rather than the outcrop of mare basalts, as they originally had been considered. In another application of our new method we demonstrate how the new processing technique of the M3 data allowed us to investigate the irregular mare patches (IMP) inside the Hyginus crater, where we are now able to map spectral parameters on the spatial scales of original resolution (140 m/pixel). The IMP formations on the lunar surface were first discovered several decades ago during the Apollo-15 mission. Since that time, about one hundred of them have been identified using the high-resolution LRO NAC images. However, their spectral properties still have not been characterized satisfactorily due to their small sizes (less than few kilometers). The M3 spectra of the IMPs inside the Hyginus crater have two peculiarities: (1) the higher spectral slope and more proliferate absorption bands that are the spectral signatures of surface immaturity, and (2) the broad absorption band near 2 μm which extends beyond 2.7 μm. The second peculiarity was interpreted as the unique mineralogic composition of IMPs’ regolith that includes spinel, a rare oxide mineral on the lunar surface. These findings are consistent with the hypothesis that these formations are the result of young (less than 1,000,000 y.o) lunar volcanic activity. The quantitative assessment of the ilmenite (FeTiO3) abundance in the lunar regolith is an important research topic in lunar surface science. Based on the fact that the distribution of the band depth near 1.5 μm in lunar reflectance spectra shows a strong correlation with ilmenite, a new quantitative assessment of the ilmenite abundance in the lunar regolith has been undertaken using the M3 data which cover the region between the Mare Tranquilities and Serenitatis. This studied region also included the Apollo-17 landing site. A comparison of the remotely and laboratory estimated ilmenite abundances indicates the correctness of the proposed method for estimating ilemenite abundances. The distribution of ilmenite reveals significant variations of this mineral content in mare basalts from 0 up to 20 weight per cent. Ti in the lunar regolith is believed to be distributed between several mineralogical components (e.g. ilmenite, ulvospinel, agglutinic and pyroclastic glasses). Sato et al., (2017) developed the approach to retrieve only the amount of total TiO2. With our new method developed in the framework of this thesis we are now able to estimate the amount of TiO2 that is a component only of ilmenite. Comparisons of the total amount of TiO2 with the ilmenite-bearing TiO2 shows that the ilmenite is the main TiO2-containing mineral of the lunar basalts. We can state that all of our results are compatible with the generally accepted modern views of the mineralogical composition of the lunar surface. They form a number of new clarifying provisions for the spectral and optical characteristics and mineralogical composition of the regolith, which is important for further studies of the formation of the Hyginus crater and rimae complex, the origin of IMPs, the flow processes, the solidification and further evolution of the basalts of Mare Tranquilitatis. The newly developed remote sensing methods, which are presented in this thesis, can be applied to the spectral data of other lunar locations, in order to estimate or refine their mineralogical composition. Further on, the generation of global spectral and optical parameters maps and a mapping of the mineralogical diversity for scientific purposes will enable the planning of future space missions and a better assessment of the Moon’s resource potential.
Keywords: Remote sensing; hyperspectral images; Fourier transform, convergence factor; the Moon's regolith