Lunar topographic model CLTM-s01 from Chang’E-1 laser altimeter

More than 3 million range measurements from the Chang’E-1 Laser Altimeter have been used to produce a global topographic model of the Moon with improved accuracy. Our topographic model, a 360th degree and order spherical harmonic expansion of the lunar radii, is designated as Chang’E-1 Lunar Topography Model s01 (CLTM-s01). This topographic field, referenced to a mean radius of 1738 km, has an absolute vertical accuracy of approximately 31 m and a spatial resolution of 0.25° (～7.5 km). This new lunar topographic model has greatly improved previous models in spatial coverage, accuracy and spatial resolution, and also shows the polar regions with the altimeter results for the first time. From CLTM-s01, the mean, equatorial, and polar radii of the Moon are 1737103, 1737646, and 1735843 m, respectively. In the lunar-fixed coordinate system, this model shows a COM/COF offset to be (?1.777, ?0.730, 0.237) km along the x, y, and z directions, respectively. All the basic lunar shape parameters derived from CLTM-s01 are in agreement with the results of Clementine GLTM2, but CLTM-s01 offers higher accuracy and reliability due to its better global samplings.

Geologic investigation and mapping of the Sinus Iridum quadrangle from Clementine, SELENE, and Chang’e-1 data

The objectives of lunar satellite remote sensing are to study lunar surface characteristics, inner structure, and its evolution history. The contents of TiO 2 and FeO are assessed from Clementine UV/VIS data for Sinus Iridum. The geologic stratigraphic units and crates are interpreted visually based on SELENE Terrain Camera (TC) images and the spatial resolution of which is up to 10 m. And the geologic ages of different stratigraphic units are calculated by the crater size-frequency distributions measurements. The gravity anomaly is generated from SELENE gravity model (SGM90d) to show its difference from Mare Imbrium. Furthermore, the thickness of lunar regolith is also derived from microwave radiometer data of Chang’e-1 satellite. Integrating these results, it shows that the Sinus Iridum is different from the Mare Imbrium in inner structure and surface sedimentation. And its history of subsidence, deposition, volcanism, and impact is described. It makes sense to the future soft-landing and sampling at potential Sinus Iridum by remote sensing geologic analysis.

Estimation of lunar titanium content: Based on absorption features of Chang’E-1 interference imaging spectrometer (ⅡM)

Two linear regression models based on absorption features extracted from CE-1 IIM image data are presented to discuss the relationship between absorption features and titanium content. We computed five absorption parameters (Full Wave at Half Maximum (FWHM), absorption position, absorption area, absorption depth and absorption asymmetry) of the spectra collected at Apollo 17 landing sites to build two regression models, one with FWHM and the other without FWHM due to the low relation coefficient between FWHM and Ti content. Finally Ti content measured from Apollo 17 samples and Apollo 16 samples was used to test the accuracy. The results show that the predicted values of the model with FWHM have many singular values and the result of model without FWHM is more stable. The two models are relatively accurate for high-Ti districts, while seem inexact and disable for low-Ti districts.

The Chang’E-1 orbiter plays a distinctive role in China’s first successful selenodetic lunar mission

The first Chinese lunar orbiter Chang'E-1 is a successful mission with many fruitful results obtained in various disciplines. The scientific data acquired by the Chang'E-1 payloads can benefit studies of the lunar origin and evolution, as well as other relevant research areas, after careful validation of the data. Among the new results, the Chang'E-1 selenodetic products are continually uncovering characteristics of the lunar surface, undersurface and inner structure. Successful lunar orbiters such as the Clementine, Lunar Prospector, KAGUYA/SELENE, Chang'E-1, Lunar Reconnaissance Orbiter and GRAIL have been revealing, with increasing clarity, global selenodetic characteristics with state-of-the-art fine resolution and high precision. In particular, the Chang'E-1 plays an important distinctive role in selenodetic exploration through enhancing lunar topography and gravity models. The gravity model has been successfully improved with a factor of two after applying the Chang'E-1 long-wavelength tracking data. Using the new models, some medium-scale lunar surface characteristics such as basins and volcanoes have been identified. Furthermore, the old mascon basins of Bouguer, gravity anomaly and craters have been discovered with the Chang'E-1 selenodetic data.

Super-resolution reconstruction and higher-degree function deformation model based matching for Chang’E-1 lunar images

This article intends to solve the matching problem of 2C level lunar images by Chang’E-1(CE-1)lunar probe satellite.A line-scanner image matching method is proposed which represents deformation by the quadric function along the camera motion direction and bases on the deformation model for a relief terrain’s imaging on sensors of the satellite borne three-line scanner camera.A precise matching is carried out for the normal view,the frontward view,and the backward view images of the CE-1 by combining the proposed method with the standard correlation method.A super-resolution(SR)reconstruction algorithm based on the wavelet interpolation of non-uniformly sampled data is also adopted to realize SR reconstruction of CE-1 lunar images,which adds the recognizable targets and explores CE-1 lunar images to the full.

Lunar digital elevation model and elevation distribution model based on Chang’E-1 LAM data

More than 8.2 million effective data samples were obtained by the Chang’E-1 Laser Altimeter (LAM).In order to produce a global topographic model of the moon with improved accuracy,a hierarchical many-knot spline method was proposed in this paper.This algorithm makes use of a hierarchy of control lattices to approximate or interpolate the LAM data.Based on the proposed algorithm,a 0.0625°×0.0625° grid of global lunar DEM was obtained and it was compared with ULCN2005,CLTMs01 and Kaguya models,respectively.At the same time,this paper explored the elevation distribution law and established the elevation distribution model.It is shown that the global lunar and nearside elevation distribution is positively skewed and leptokurtic normal distribution,and the farside elevation distribution is a positively skewed and platykurtic normal distribution.

Mapping of the lunar surface by average atomic number based on positron annihilation radiation from Chang'e-1

A map of the average atomic number of lunar rock and soil can be used to differentiate lithology and soil type on the lunar surface.This paper establishes a linear relationship between the average atomic number of lunar rock or soil and the flux of position annihilation radiation(0.512-Me V gamma-ray) from the lunar surface.The relationship is confirmed by Monte Carlo simulation with data from lunar rock or soil samples collected by Luna(Russia) and Apollo(USA) missions.A map of the average atomic number of the lunar rock and soil on the lunar surface has been derived from the Gamma-Ray Spectrometer data collected by Chang'e-1,an unmanned Chinese lunar-orbiting spacecraft.In the map,the higher average atomic numbers(ZA > 12.5),which are related to different types of basalt,are in the maria region;the highest ZA(13.2) readings are associated with Sinus Aestuum.The middle ZA(~12.1) regions,in the shape of irregular oval rings,are in West Oceanus Procellarum and Mare Frigoris,which seems to be consistent with the distribution of potassium,rare earth elements,and phosphorus as a unique feature on the lunar surface.The lower average atomic numbers(ZA < 11.5)are found to be correlated with the anorthosite on the far side of the Moon.

SPACE PROBE Chang’e-1 Withstands Test

China’s pioneering lunar probe Chang’e-1 made it through its first lunar eclipse on February

Laser altimetry data of Chang'E-1 and the global lunar DEM model

The Laser AltiMeter (LAM), as one of the main payloads of Chang'E-1 probe, is used to measure the topography of the lunar surface. It performed the first measurement at 02:22 on November 28th, 2007. Up to December 4th 2008, the total number of measurements was approximately 9.12 million, covering the whole surface of the Moon. Using the LAM data, we constructed a global lunar Digtal Elevation Model (DEM) with 3 km spatial resolution. The model shows pronounced morphological characteristics, legible and vivid details of the lunar surface. The plane positioning accuracy of the DEM is 445 m (1σ), and the vertical accuracy is 60 m (1σ). From this DEM model, we measured the full range of the altitude difference on the lunar sur-face, which is about 19.807 km. The highest point is 10.629 km high, on a peak between crater Korolev and crater Dirichlet-Jackson at (158.656°W, 5.441°N) and the lowest point is -9.178 km in height, inside crater Antoniadi (172.413°W, 70.368°S) in the South Pole-Aitken Basin. By comparison, the DEM model of Chang'E-1 is better than the USA ULCN2005 in accuracy and resolution and is probably identical to the DEM of Japan SELENE, but the DEM of Chang'E-1 reveals a new lowest point, clearly lower than that of SELENE.

The global image of the Moon obtained by the Chang'E-1:Data processing and lunar cartography

The global lunar image of the first phase of Chinese Lunar Exploration Program is the first image that covered all over the surface of the Moon. It will serve as a critical foundation for succeeding exploration and scientific research. In this paper, the acquisition, characteristics, and data quality of Chang'E-1 CCD image data are described in detail. Also described are the methodology and procedure of data processing. According to rule of planetary cartography, the image data have been processed, geometrically corrected, and then mosaicked and merged in a scale of 1:2.5 million. The results of data processing and charting show that the image data of Chang'E-1 CCD and their geometric precision meet the demand of charting a map in the scale of 1:2.5 million. The relative geometric positioning precision of the global image is better than 240 m, and the absolute geometric positioning precision is slightly better than that of the ULCN2005 and Clementine lunar basemap (V2.0). The plane positioning precision is approximately 100-1500 m. This global image proves to be the best global image of the Moon so far in terms of space coverage, image quality, and positioning precision.

Primary scientific results of Chang'E-1 lunar mission

The strategic plan for the development of the unmanned Chinese Lunar Exploration Program is characterized by three distinct stages: "orbiting around", "landing on" and "returning from" the Moon. The first Chinese lunar probe, Chang'E-1, which was successfully launched on October 24th, 2007 at Xichang Satellite Launch Center, and guided to crash on the Moon on March 1st, 2009, at 52.36°E, 1.50°S, in the north of Mare Fecunditatis, is the first step towards the "orbiting around" stage. The Chang'E-1 mission lasted 495 days, exceeding the expected life-span by about four months. A total of 1.37 TB raw data was received from Chang'E-1. It was then processed into 4 TB scientific data products at various levels. Many scientific results have been obtained by analyzing these data, including especially the "global lunar image from the first Chinese lunar explora- tion mission". All scientific goals of Chang'E-1 have been achieved. It provides much useful materials for further advances of lunar sciences and planetary chemistry. Meanwhile, these results will serve as a firm basis for future Chinese lunar missions.

Absolute calibration of the Chang'E-1 IIM camera and its preliminary application

The interference imaging spectroradiometer (IIM) onboard the first lunar satellite of China "Chang'E-1" can now provide approximately global high spectral and spatial resolution reflectance spectra of the Moon. It is the essential instrument with which to accomplish one of the four missions of the first lunar satellite of China. As the current data provided by the Lunar Exploration Program Center and National Astronomical Observatories (NAOC) are not reflectance and the sensor response is inhomogeneous in the line direction,users can not use the current data directly. Moreover,due to the narrow band range,IIM data cannot cover the absorption peak of the mafic minerals of the Moon completely,which limits its ability for identifying minerals. The main objective of this study is to describe the methods for absolute calibration,correction and acquiring the absorption center of minerals for IIM data. The results from our study show that in the space domain the sensor response decreases toward the left,and in the spectral domain the response of the longer bands is more inhomogeneous than that of the shorter bands. After the calibration and correction,the reflectance of IIM matches the earth-based telescopic spectra well,which suggests the possible use of the processed data in the geological research. A high correlation was found between the absorption center and the wavelength at which the first derivative equals 0,i.e.,the so-called Stagnation Point in the mathematical sense. In the end,we show a preliminary applied study of the two craters with diameter larger than 35 km using the calibrated data. The spectra of IIM data show that the lunar crust has compositional diversity within the km scale. Pure anorthosite may be found on the wall and floor of the Aristarchus crater with the map of absorption center,which indicates that anorthosite is ubiquitously present within the lunar crust. IIM,with its capacity to acquire lunar composition at the regional and global scale,will contribute to the research of lunar origin and evolution.

Triaxial ellipsoid models of the Moon based on the laser altimetry data of Chang'E-1

Lunar geodetic parameters, which play an important role in lunar exploration, can be calculated from the gravity and topography data. With the CE-1 altimetry data and LP gravity model, we calculate such geodetic parameters as the principle moment of inertia, the principle inertia axes, equatorial radius, polar radius, mean radius, flattening and offset between center of mass and center of figure (DCOM-COF). According to the CE-1 altimetry data and the above geodetic parameters, a tri-axial ellipsoid (CE-1-LAM-GEO) and a tri-axial level ellipsoid (CE-1-LAM-LEVEL) are calculated individually, providing mass center and figure center offset (DCOM-COF) and parameters more reliable in direction and magnitude.

Registration of Correspondent Points in the Stereo-Pairs of Chang'E-1 Lunar Mission Using SIFT Algorithm

In this article, an appropriate strategy for registration of correspondent points in the stereo-pairs of Chang’E-1 lunar mission has been introduced. It consists of area-based method and feature-based method as two steps. Firstly, one subimage was extracted from nadir image as reference image. Making use of area-based method, another subimage which is called target image can be obtained from backward or forward image overlapping the same region of lunar surface with reference image. Secondly, feature points of each subimage can be extracted by SIFT （scale invariant feature transform） algorithm. Lastly, for each feature point given in reference image, the position of correspondence in target image can be estimated according to the parameters of Chang’E-1 lunar orbiter. In contrast to standard SIFT matching algorithm, the method proposed in this article can narrow the search space and accelerate the speed of computation while achieving reduction of the percentage of false registration.

嫦娥一号卫星太阳风离子探测器离子流量反演太阳风参数与初步结果分析

嫦娥一号卫星（Chang’E．1）上搭载的两台太阳风离子探测器（SWID—A／B）是国际上首次在200km极月轨道观测等离子体环境的探测仪器．SWID—A／B的科学目标是探测月球附近等离子体与月球的相互作用，获得月球附近的太阳风速度、密度和温度．太阳风离子探测器的观测数据是各能量成分离子流量的直接反映，包含了太阳风离子的速度、密度和温度信息．本文设计了一种利用离子流量数据反演太阳风速度、密度和温度的算法，并通过模拟太阳风离子注入探测器的过程，验证了算法的可行性．对月球附近太阳风离子基本特征的分析研究表明，在太阳活动低年，空间环境扰动水平相对较低时，行星际太阳风运动到月球附近后依然保持着相同的变化趋势；太阳风离子的速度和密度与在上游行星际空间时相近；太阳风离子的温度则比在上游行星际空间时高103K．

Global absorption center map of the mafic minerals on the Moon as viewed by CE-1 IIM data

Determining the global distribution of minerals on the Moon has been an important goal of lunar science. Hyperspectral remote sensing is an important approach to acquiring minerals on the Moon on the global scale. The wavelength of the absorption band center is the key parameter for identifying minerals with reflectance spectra as well as remote sensing data. The global absorption center map of the mafic minerals of the Moon was produced for the first time with the Chang’E-1 IIM data. This map shows the global distribution of mafic minerals such as orthopyroxenes, clinopyroxenes, and olivine and even plagioclase feldspar of the Moon. The validation for some representative areas indicates that the global map is reliable and even more detailed than the results derived from Clementine-data. Moreover, our method is insensitive to the topography and viewing and illumination geometries. The global absorption band center map not only contributes to the lunar science research, but also has other implications to be further studied. Moreover, the preprocessing methods such as calibration and correction introduced in this study can be useful in other research with IIM data.

Bouguer gravity anomaly of the Moon from CE-1 topography data:Implications for the impact basin evolution

In this study,the terrain correction for lunar free-air gravity anomaly (FAGA) is calculated in spherical coordinates based on the global topography data detected by the laser altimeter on Chang'E-1 (CE-1). The obtained lunar Bouguer gravity anomaly (BGA) reveals density irregularities of the interior mass. BGA is important in characterizing the mascon basins. According to the BGA of the Moon,the South Pole-Aitken (SPA) basin is considered the largest mascon basin on the Moon,and the feature of BGA in the basin implies the impacting direction. Further,the mascon basins seem to be classified into two types,Type Highland and Type Plain. For the mascon basins of Type Highland the dense materials mainly come from the shallow crust,which are associated with the basalt deposits. The other type,Type Plain,includes mascon basins whose major dense materials may be located deep at the litho-sphere,corresponding to the uplifted mantle.

New features of the Moon revealed and identified by CLTM-s01

Previous analyses showed a clear asymmetry in the topography,geological material distribution,and crustal thickness between the nearside and farside of the Moon. Lunar detecting data,such as topography and gravity,have made it possible to interpret this hemisphere dichotomy. The high-resolution lunar topographic model CLTM-s01 has revealed that there still exist four unknown features,namely,quasi-impact basin Sternfeld-Lewis (20°S,232°E),confirmed impact basin Fitzgerald-Jackson (25°N,191°E),crater Wugang (13°N,189°E) and volcanic deposited highland Yutu (14°N,308°E). Furthermore,we analyzed and identified about eleven large-scale impact basins that have been proposed since 1994,and classified them according to their circular characteristics.

Origin of pit chains in the floor of lunar Copernican craters

There are small pit chains in the floor of lunar Copernican craters. They are usually so small in scale that there are few lunar spacecrafts to detect their detailed morphology. Combining camera data from Lunar Orbiter, Lunar Reconnaissance Orbiter (LRO), Kaguya and Chang’e-1 missions, 5 representative large Copernican craters on various terrains of the lunar surface are chosen to study the origin of the pit chains in the crater floor. The morphology and distribution characteristic of the pit chains are referred by the high resolution images in this research. It is suggested that it is the magma activities from the subsurface magma layer combining with the existence of fractures and faults under the crater floor that leaded the formation of the pit chains. The model is further verified and discussed using the regolith thickness data in the crater floor. Our model suggests that the pit chains are still developing in the floor of the Copernican craters and the Moon may not be totally cold. Finally, the model limitation and potential future work are discussed based on available data.

A digital open-loop Doppler processing prototype for deep-space navigation

A prototype based on digital radio technology with associated open-loop Doppler signal processing techniques has been developed to measure a spacecraft's line-of-sight velocity. The prototype was tested in China's Chang'E-1 lunar mission relying on S-band telemetry signals transmitted by the sat-ellite,with results showing that the residuals had a RMS value of ～3 mm/s (1σ ) using 1-sec integration,which is consistent with the Chinese conventional USB (Unified S-Band) tracking system. Such preci-sion is mainly limited by the short-term stability of the atomic (e.g. rubidium) clock at the uplink ground station. It can also be improved with proper calibration to remove some effects of the transmission media (such as solar plasma,troposphere and ionosphere),and a longer integration time (e.g. down to 0.56 mm/s at 34 seconds) allowed by the spacecraft dynamics. The tracking accuracy can also be in-creased with differential methods that may effectively remove most of the long-term drifts and some of the short-term uncertainties of the uplink atomic clock,thereby further reducing the residuals to the 1 mm/s level. Our experimental tracking data have been used in orbit determination for Chang'E-1,while other applications (such as the upcoming YH-1 Mars orbiter) based on open-loop Doppler tracking will be initiated in the future. Successful application of the prototype to the Chang'E-1 mission in 2008 is believed to have great significance for China's future deep space exploration.