The subsurface structure and stratigraphy of the Chang’E-4 landing site:orbital evidence from small craters on the Von Kármán crater floor

Chang’E-4(CE-4)successfully landed on the floor of the Von Kármán crater within the South Pole-Aitken basin(SPA).One of its scientific objectives is to determine the subsurface structure and the thickness of lunar regolith at the landing site and along the traverse route of the Yutu-2 rover.Using orbital data,we employed small craters(diameters<1 km)on the floor of the Von Kármán crater as probes to investigate the subsurface structure and stratigraphy of the CE-4 landing site.In this study,40 dark-haloed craters that penetrate through the surface Finsen ejecta and excavate underlying mare deposits were identified,and 77 bright ray craters that expose only the underlying fresh materials but do not penetrate through the surface Finsen ejecta were found.The excavation depths of these craters and their distances from the Finsen crater center were calculated,and the thickness distribution of Finsen ejecta on the Von Kármán floor was systematically investigated.The boundary between Finsen ejecta and underlying mare basalt at the CE-4 landing site is constrained to a depth of 18 m.We have proposed the stratigraphy for the CE-4 site and interpreted the origins of different layers and the geological history of the Von Kármán crater.These results provide valuable geological background for interpreting data from the Lunar Penetrating Radar(LPR)and Visible and Near-infrared Imaging Spectrometer(VNIS)on the Yutu-2 rover.The CE-4 landing site could provide a reference point for crater ejecta distribution and mixing with local materials,to test and improve ejecta thickness models according to the in situ measurements of the CE-4 LPR.

Latest Scientific Results of China's Lunar and Deep Space Exploration(2022–2024)

China has successfully launched six lunar probes so far.From Chang'E-1 to Chang'E-4,they completed the circling,landing and roving exploration,of which Chang'E-4 was the first landing on the far side of the Moon in human history.Chang'E-5 was launched in December 2020,bringing back 1731 g of lunar soil samples.Through the detailed analysis of the samples,the scientists understand the history of late lunar volcanism,specifically extending lunar volcanism by about 800 million to 1 billion years,and proposed possible mechanisms.In addition,there are many new understandings of space weathering such as meteorite impacts and solar wind radiation on the Moon.China's first Mars exploration mission Tianwen-1 was successfully launched in July 2021.Through the study of scientific data,a number of important scientific achievements have been made in the topography,water environment and shallow surface structure of Mars.This paper introduces the main scientific achievements of Chang'E-4,Chang'E-5 and Tianwen-1 in the past two years,excluding technical and engineering contents.Due to the large number of articles involved,this paper only introduces part of the results.

Overview of the Latest Scientific Achievements of Chang'E-4 Mission of China's Lunar Exploration Project

On 3 January 2019,the Chang’E-4 probe successfully landed in the Von Kármán crater in the South Pole-Aitken Basin on the far side of the Moon.On 4 January,the Yutu-2 rover was successfully separated from the lander and the scientific payloads were powered on to conduct scientific exploration.It was the first time that manmade probe achieved soft landing and roving on the far side of the Moon.Based on the data obtained by scientific payloads on the Chang’E-4,the research team obtained geological information such as landing area topography,structure and composition;demonstrated the existence of deep materials—mainly olivine and low-calcium pyroxene in the South Pole-Aitken Basin;achieved high-precision imaging of the layered structure of lunar subsurface in the roving area;discovered carbonaceous spheroidal meteorite residues and impact glass;preliminarily revealed the geological evolutionary history of the South Pole-Aitken Basin;for the first time,obtained information of the radiation dose of energetic particles at the lunar surface and the structure of the lunar neutral atomic energy spectrum;discovered the lunar mini-magnetosphere and contributed new knowledge of the radiation hazards at the lunar surface.This article summarizes the latest scientific achievement from the Chang’E-4 mission over the past three years.

Enhancing the vertical resolution of lunar penetrating radar data using predictive deconvolution

The Yutu-2 rover onboard the Chang’E-4 mission performed the first lunar penetrating radar detection on the farside of the Moon.The high-frequency channel presented us with many unprecedented details of the subsurface structures within a depth of approximately 50 m.However,it was still difficult to identify finer layers from the cluttered reflections and scattering waves.We applied deconvolution to improve the vertical resolution of the radar profile by extending the limited bandwidth associated with the emissive radar pulse.To overcome the challenges arising from the mixed-phase wavelets and the problematic amplification of noise,we performed predictive deconvolution to remove the minimum-phase components from the Chang’E-4 dataset,followed by a comprehensive phase rotation to rectify phase anomalies in the radar image.Subsequently,we implemented irreversible migration filtering to mitigate the noise and diminutive clutter echoes amplified by deconvolution.The processed data showed evident enhancement of the vertical resolution with a widened bandwidth in the frequency domain and better signal clarity in the time domain,providing us with more undisputed details of subsurface structures near the Chang’E-4 landing site.

Auto-compensation of velocity-height ratio for Chang’E-2 satellite CCD stereo camera

The TDI-CCD imaging method using auto-compensation of velocity-height ratio (VHR) was applied to Chang’E-2 satellite CCD stereo camera.Factors that influence the image quality of the camera were discussed,among which the mismatch error in VHR was found to be the main cause.An auto-compensation scheme for VHR was developed.The validity and effectiveness were proved by the on-orbit high quality images.

Positioning reduction in the real-time phase of Chang'E-2 satellite

The precision of VLBI tracking delays and the positioning reduction results during the real-time tracking phase of the Chang'E-2 satellite are statistically analyzed.The application of the positioning reduction to the real-time monitoring of pivotal arcs of the Chang'E-2 satellite is discussed.The technical specifications of the tests of tracking and control systems in X-band are estimated and evaluated via the positioning reduction method.Useful methodology and software are prepared and practical experience in engineering and technology is accumulated for the follow-up lunar and deep space explorations of China.

Overview of the Latest Scientific Results of China’s Lunar Exploration Program

China’s Chang’E-4 probe successfully landed on 3 January 2019 in Von Kármán crater within the South Pole-Aitken(SPA)basin on the lunar far side.Based on the data acquired by the scientific payloads onboard the lander and the rover,the researchers obtained the related information such as the geologic and tectonic setting of the landing area,compositional characteristics of the landing surface materials,dielectric permittivity and density of the lunar soil.The experiments confirmed the existence of materials dominated by olivine and low-calcium pyroxene in the SPA basin on the lunar far side,which preliminary revealed the geological evolution history of the SPA basin and even that of the early time lunar crust,as well as the tectonic setting and formation mechanism of the materials in the lunar interior.The researchers also investigated the particle radiation,Linear Energy Transaction(LET)spectrum,and so forth on the lunar surface.The low-frequency radio observations were carried out on the lunar far side for the first time as well.This article summarizes the latest scientific results in the past years,focusing on the Chang’E-4 mission.

高分四号卫星在洪泽湖汛期水体范围变化监测中的应用

洪泽湖是淮河中下游的分界线,对其汛期水体范围变化进行监测具有重要意义。文章发挥高分四号卫星数据高时间分辨率的特点,依据水体指数模型自动化提取水体范围,通过基于相关分析的变化检测算法快速提取洪泽湖水体范围变化,开展洪泽湖汛期水体范围变化的监测。结果表明:在同一汛期范围内,水体面积与周长在一定范围内呈反比;在汛期不同月份内,水体面积有显著的变化,增减同时存在。监测结果可为区域灾害风险评估和损失评估提供决策支持。

基于“高分四号”卫星数据的水体提取效果评价

"高分四号"卫星具有静止轨道卫星高时间分辨率和中高空间分辨率的特点,可以实现对水体面积及变化的大范围实时监测,有效支撑洪涝灾害应急救助工作。为了验证其对水体面积及其变化的监测能力,文章分别利用区域生长法和水体指数法,在开展全国水体面积变化监测基础上,针对与同期"高分一号"卫星16m分辨率多光谱相机及美国Terra卫星的中分辨率成像光谱仪数据等卫星的监测结果展开对比,结果显示,与其他极轨卫星监测结果相比,"高分四号"卫星可以有效开展水体面积及变化监测。但是,鉴于"高分四号"卫星50m像元分辨率,相比更高分辨率遥感影像的水体提取结果,"高分四号"卫星数据提取的水体外部轮廓较为粗糙。在针对规模较小洪涝灾害监测方面可能存在一定误差,仍然需要再进一步开展评价。

嫦娥四号任务月球中继链路飞控工作模式设计

介绍了嫦娥四号任务月球背面中继链路飞控工作模式设计方案。针对月球背面探测需要克服地面测控网与月球背面探测器之间存在地基测控盲区的需求,嫦娥四号任务在工程设计上采用在月球背面地月连线上的L2点布设中继星的方式,在世界上首次采用地月L2点中继星实现对地对月中继通信。从嫦娥四号月球背面探测任务飞控需求出发,分析将中继星引入深空探测任务天地测控大回路对飞控实施的主要影响,设计了基于月球中继星的深空探测任务飞控模式,嫦娥四号任务飞控工作取得圆满成功,验证了该模式的正确性和有效性。

基于单景高分四号卫星多光谱影像的舰船运动特征检测

高分辨率地球同步轨道(GEO)遥感卫星技术能够在短时间内对大范围海域进行高频重复监测,有望近实时地获取海上舰船运动特征。以广东省珠江伶仃洋的南部海域为研究区,基于单景高分四号卫星多光谱影像,使用梯度阈值方法对海上运动舰船进行检测,结果表明:①利用单波段高分四号多光谱影像能够检测出船位与航向,船位平均误差为80.46 m(相当于1.61个图像分辨单元),航向检出率为74.36%,航向绝对误差为8.65°。②利用单景高分四号影像能够检测出航向与船速,航向精度为98.96%,平均绝对误差为8.78°,船速精度为83.0%,平均绝对误差为1.41 m/s。研究表明高分四号卫星能够用于海上舰船近实时遥感监测,在海上舰船运动特征检测方面具有独特优势和巨大的应用潜力。

Construction of a virtual lunar environment platform

Many of the world’s powerful and wealthy nations,including China,have devoted both large amounts of funding and considerable promotion to lunar research and exploration.The launch of Chinese Chang’e-1 satellite and the construction of the scientific observation data platform created a favourable opportunity for research into the lunar geometrical,physical and chemical environment.Based on this background,a Wide Area Network(WAN)based virtual lunar environment was constructed for observation data sharing and further exploration.The systematic architecture and framework were introduced and then strategies of mass data(e.g.lunar digital elevation model,lunar digital orthophoto map and typical thematic lunar data)organisation,integration,management and scheduling were then set up to achieve the 3D visualisation of typical lunar geomorphic features.Furthermore,the integration method of 3D lunar data and the process model of impact craters were studied;thus,the whole lunar and celestial collision process could be dynamically simulated.The results indicate that the WAN-based virtual lunar platform can be used effectively for public information sharing,scientific exploration and further to promote the development of deep space exploration in China.