Chang'e-1 Gamma Ray Spectra Data Analysis And Processing For Lunar Detection

When the nuclei of Lunar surface material bombarded by cosmic ray particles, it will produce its characteristicγ-ray excitation; besides, a number of natural radioactive elements can also spontaneously produceγ-rays. Different elements can produce gamma-ray spectra with different energy. Therefore, by measuring the energy and flux of these characteristics spectra, we can get the composition and abundance of lunar surface materials.China Lunar Exploration Program was the first step of deep space exploration, its successful implementation was breakthrough of China's aerospace exploration. At present, lunar has become the focus of scientists in many countries, there are a variety of unique mineral and energy resources on the moon for human development, and is an important complement and reserves to the Earth's resources, also it has a profound impact in human society for sustainable development.This paper focused on getting the radioactive composition and abundance of lunar surface materials, analyzed the data of gamma ray spectrometer on the Chang'E-1 during one year scientific exploration. After compared with other analyzing result of lunar detection mission, following conclusions can be drawn.1, After selection and calibration for 5,449,778 spectra of 2C level data, we checked the overall distribution map of elements, and found that there was some abnormally high value band shape distribution. So we extracted the latitude, longitude, measuring status and time parameters of Chang'E-1 satellite from documents, map the latitude and longitude of abnormal 2C-level files, found the possible causes, and removed the abnormal orbit data, then effectively eliminating the abnormal high counts band shape distribution in the results.2, In order to decreasing the statistical fluctuation in radioactive detection, we take Daubechies-4 for wavelet orthogonal decomposition. By its energy conservation characteristic, we can ensure it doesn't increase noise energy in inverse wavelet transform. After setting the unbiased estimation threshold by non-linear threshold function, we reconstructed the smoothing spectrum with stability of count value, which was of great significance for the accuracy of quantitative element analysis.3, Based on analyzing of some background estimation methods, we proposed the Trend line Peak Strengthening for Background Estimation (TPSBE) method, decomposited the spectrum in frequency domain, get the trend line and enhanced the characteristic peaks. Then, we found the position of peaks and valleys by biorthogonal wavelet decomposition. After correction of the result, we estimated the background by interpolation. Using this method, we can well extract the information of elemental characteristic peaks, especially for the low energy band section in which the weak peaks information were submerged in high background counts.4, For the overlapping peaks in the spectra, such as the characteristic peaks of potassium and magnesium, we decomposited them by Gaussian function fitting method according to minimum mean square error principle. The result of lunar radioactive elements distribution was clearly shown by equal-area map, contour map, spherical 3D map.5, According to the distribution map of U, Th, K elements, there was a significant correlation-ship, all of them were mainly distributed in the northern near side of lunar, within an big triangular region constituted by west longitude 70°, north latitude 50°; West longitude 20°, south latitude 30°; east longitude 50°, north latitude 70°north latitude. Particularly in the south of the Mare Nubium, Mare Humorum, the Oceanus procellarum, were significant high-value distribution. Outside the big triangular region the counts were generally low. While in the Antarctic Aiken Basin there was a relatively high value area, but much lower than that in the big triangular region.6, Comparing Chang'E-1 GRS's result with that of Apollo, Lunar Prospector, and Kaguya, although different mission with different detecting devices, in different satellite orbit, during different time, the data processing result for three radioactive elements of Uranium, thorium, potassium presented high consistency in distribution map, which could objectively reflect the main radioactive element composition and distribution on the moon,.