一种基于自动特征学习的陨石坑区域检测算法

基于陨石坑的视觉导航技术成为一种新颖的高精度空间探测自主导航方式,如何从导航图像中精确地提取陨石坑区域是实现基于陨石坑视觉导航的首要条件。针对这一问题,根据陨石坑导航图像特点,提出了一种基于自动特征学习的陨石坑区域检测算法。首先,基于最大稳定极值区域检测算法提取陨石坑候选区域;其次,利用卷积神经网络（CNN）自动学习提取候选区域的特征;最后,通过支持向量机（SVM）实现候选区域的精确分类,得到真实的陨石坑区域。大量的仿真实验表明:与传统的基于人工特征的陨石坑区域检测算法相比,提出的基于自动特征学习的陨石坑区域检测算法具有更高的检测精度和更好的鲁棒性,在通用火星表面陨石坑数据集上,所提算法的F₁度量指标较于传统算法高出8%,可以广泛地应用于基于陨石坑的视觉导航算法中的陨石坑区域提取,为基于陨石坑视觉导航算法提供精确的导航路标输入。      

一种基于多尺度边缘提取的陨石坑检测算法

针对星体表面的陨石坑可用于探测器的自主导航、障碍识别等任务,提出一种基于多尺度边缘提取的陨石坑检测算法。该算法首先利用高斯金字塔得到不同尺度的陨石坑图像;其次,针对不同尺度的陨石坑图像,利用EDPF边缘提取算法对陨石坑进行边缘提取,并连接关键边缘像素点为直线段来近似表示图像边缘;然后将具有相同偏转方向的边缘直线段连接成圆弧,并将有相似半径和中心的圆弧拟合成候选圆和椭圆;最后对候选圆、椭圆进行验证。该算法的优点在于,能够准确地检测出陨石坑,有较高的检测率,且对存在较多陨石坑的图像有较好的检测结果。     

火星沟壑地形的最清晰照片

火星全球勘测者(MGS)探测器携带的火星轨道站照相机(MOC)近日拍摄到一张极其清晰的火星沟壑照片,如右图所示。位置在火星南半球牛顿陨石坑东脊梁     

来自航天器的重大发现

<正>月球和火星上存在水2009年9月和11月,美国科学家两次发布月球上确实存在水并在火星赤道附近的陨石坑内也存在水冰的重大发现,对人类探索和登陆月球、远征火星增添新的希望与动力。     

地基行星大气掩星观测资料流程和数据整理

在中国火星探测萤火一号(YH-1)计划中, 包括了地基掩星观测反演火星大气的科研任务. 观测资料整理是反演流程的第一步. 本文描述了地基火星大气掩星观测处理软件系统的观测数据流程和观测资料整理模块,并详细介绍了观测资料整理模块的结构和功能, 其中包括时间系统转换、历表插值、坐标系变换、信号时延改正以及掩星平面建立. 利用行星数据系统公布的火星快车无线电科学数据和由SPICE得到的地球、火星历表以及火星快车的轨道数据, 结合本文的算法, 得到了一些实验结果.      

每月小抄

[天文]美国航空航天局科学家近日在由火星勘测轨道器上的高分辨率成像科学实验相机拍摄的一张火星照片上发现了一个罕见的洞穴。照片显示。在火星帕蒙尼斯火山的斜坡上，出现一个明显的陨石坑状洞口。陨石坑似乎通向一个地下洞穴，洞口的右侧被部分照亮。这个洞口直径大约为35米，深度大约为20米。     

开启火星的航空时代:十问机智号火星直升机

美国毅力号火星车于美国东部时间2021 年 2 月 18 日 3 时 43 分,在火星赤道以北的杰泽罗陨石坑成功着陆,并传回火星图片.它将至少花费一个火星年(约687地球日)对着陆区域进行探索. "毅力号"是继好奇号火星车之后,美国宇航局(NASA)造访火星表面的第九个探测器,第五辆漫游车."毅力号"任务的目标包括寻找...     

揭秘“好奇”号制动伞

如果一切顺利的话,美国航空航天局的"好奇"号火星车将于2012年8月5日在太空起重机的帮助下在火星表面着陆。在太空起重机利用绳索和制动火箭让"好奇"号慢慢降落盖尔陨石坑之前,制动降落伞将首先打开,使"好奇"号以及太空起重机的速度降     

基于光谱知识的高光谱图像自动识别方法

针对传统高光谱图像矿物识别方法未能充分利用矿物光谱诊断吸收特征与矿物光谱知识、识别过程人为干预多等问题,提出了一种基于光谱知识的高光谱图像自动识别方法.该方法引入了基于光谱吸收特征与波形特征的光谱知识作为自动识别的标准,利用连续统去除操作增强光谱吸收特征,采取基于光谱主次吸收特征的识别决策策略,建立多级约束准则以提高识别精度及避免误识别,通过利用模拟数据进行算法精度评价并应用航空高光谱成像仪AVIRIS(Airborne Visible/Infrared Imaging Spectrometer)数据进行应用分析与验证.结果表明:当图像信噪比大于200时,识别准确率可以达到80.3%,能够得到良好的识别结果以及较高的精度,并实现了基于高光谱图像的矿物自动识别.     

机遇号仍然很健康

火星探测器机遇号目前仍然很健康。在1016个火星日,机遇号到达维多利亚陨石坑的BottomlessBay并且开始科学考察。它的里程计统计总共已行走了9584.69米。在第1018个     

利用CRISM数据探测火星表面含水矿物及其演化

火星表层矿物识别是了解火星大气环境变化、表层地质环境的关键因素。通过确定火星表层矿物,分析矿物特性,了解火星的环境状态、地质演化以及火星的未来适居性。火星勘测轨道器(Mars reconnaissance orbiter,MRO)上搭载的紧凑型侦察成像仪(compact reconnaissance imaging spectrometer for Mars,CRISM)是针对火星矿物探测的最新的高光谱成像仪,以很高的光谱分辨率覆盖可见光至近红外波段,为火星表面的矿物分布及区域填图提供了可能。通过光谱匹配及计算CRISM光谱参数综合产品,分析了火星Jezero以及Holden撞击坑内的矿物成分及其演化。Jezero与Holden因其复杂而关键的地质特征,被列为火星2020登陆任务的备选登陆点。对这两个地点的矿物探测与填图分析不仅可进一步分析火星典型地质特征以及演化,而且还可以为未来的火星登陆点分析提供现实意义。在研究区域已检测到与水成蚀变相关的含水硅酸盐类以及碳酸盐类与含水硫酸盐类。水合矿物增加了这些区域曾经含水的可能性,且矿物的多样性表明研究区地质环境经历了不同的变化,其中Jezero地区不同于火星的绝大多数地区从中性环境到酸性环境的演化,有可能经历了从中性环境到碱性环境的演化。     

A machine learning approach to crater detection from topographic data

Craters are distinctive features on the surfaces of most terrestrial planets. Craters reveal the relative ages of surface units and provide information on surface geology. Extracting craters is one of the fundamental tasks in planetary research. Although many automated crater detection algorithms have been developed to exact craters from image or topographic data, most of them are applicable only in particular regions, and only a few can be widely used, especially in complex surface settings. In this study, we present a machine learning approach to crater detection from topographic data. This approach includes two steps: detecting square regions which contain one crater with the use of a boosting algorithm and delineating the rims of the crater in each square region by local terrain analysis and circular Hough transform. A new variant of Haar-like features (scaled Haar-like features) is proposed and combined with traditional Haar-like features and local binary pattern features to enhance the performance of the classifier. Experimental results with the use of Mars topographic data demonstrate that the developed approach can significantly decrease the false positive detection rate while maintaining a relatively high true positive detection rate even in challenging sites.     

Detection of sub-kilometer craters in high resolution planetary images using shape and texture features

Counting craters is a paramount tool of planetary analysis because it provides relative dating of planetary surfaces. Dating surfaces with high spatial resolution requires counting a very large number of small, sub-kilometer size craters. Exhaustive manual surveys of such craters over extensive regions are impractical, sparking interest in designing crater detection algorithms (CDAs). As a part of our effort to design a CDA, which is robust and practical for planetary research analysis, we propose a crater detection approach that utilizes both shape and texture features to identify efficiently sub-kilometer craters in high resolution panchromatic images. First, a mathematical morphology-based shape analysis is used to identify regions in an image that may contain craters; only those regions - crater candidates - are the subject of further processing. Second, image texture features in combination with the boosting ensemble supervised learning algorithm are used to accurately classify previously identified candidates into craters and non-craters. The design of the proposed CDA is described and its performance is evaluated using a high resolution image of Mars for which sub-kilometer craters have been manually identified. The overall detection rate of the proposed CDA is 81%, the branching factor is 0.14, and the overall quality factor is 72%. This performance is a significant improvement over the previous CDA based exclusively on the shape features. The combination of performance level and computational efficiency offered by this CDA makes it attractive for practical application.     

γ-ray spectroscopy in Mars orbit during solar proton events

Understanding the evolution of Mars requires determining the composition of the surface and atmosphere of the planet. The European Space Agency’s ExoMars rover mission, which is expected to launch in 2016, is part of the Aurora programme. The instruments on the rover will search for evidence of life on Mars and will map a sub-section of the Martian surface, extracting compositional information. Currently our understanding of the bulk composition (and mineralogy) of Mars relies on orbital data from instruments on-board satellites such as 2001 Mars Odyssey, Mars Reconnaissance Orbiter and Mars Express, in addition to in-situ instrumentation on rovers such as Spirit and Opportunity. γ-ray spectroscopy can be used to determine the composition of Mars, but it has yet to be successfully carried out in-situ on Mars. This study describes some of the results obtained from the γ-ray spectrometer on 2001 Mars Odyssey during solar proton events and discusses whether the increased emissions are useful in γ-ray spectroscopy. The study shows that although increased γ-ray emissions were expected from the Martian surface during a solar proton event, they were not detected from orbit probably due to insufficient signal-to-background. However, this does not preclude the possibility of measuring changes in γ-ray flux corresponding to changes in solar activity on the surface of the planet.     

The first new application of the Mathematical Theory of Stochastic Processes to lunar and planetary science: Topography-Profile Diagrams of Mars

The Mathematical Statistics Theory (MST) and the Mathematical Theory of Stochastic Processes (MTSP) are different branches of the more general Mathematical Probability Theory (MPT) that can be used to investigate physical processes through mathematics. Each model of a stochastic process, according to MTSP, can provide one or more interpretations in the MST domain. A large body of work on impact crater statistics according to MST exists, showing cumulative crater frequency (N km⁻²) as a function of age (years) for some particular crater diameter. However, this is only one possible representation in the MST domain of the bombardment of the planetary surface modeled as a stochastic process according to MTSP. The idea that other representations are possible in the MST domain of the same stochastic process from MTSP has been recently presented. The importance of the approach is that each such mathematical-based interpretation can provide a large amount of new information. Coupled with MOLA data, Topography-Profile Diagrams (TPD) are one of the many examples that can provide a large amount of new information regarding the history of Mars. TPD consists of: (1) Topography-Profile Curve (TPC), which is a representation of the planet’s topography, (2) Density-of-Craters Curve (DCC), which represents density of craters, (3) Filtered-DCC (FDCC), which represents DCC filtered by a low-pass filter, included with the purpose of reducing the noise, and (4) Level-of-Substance-Over-Time Curve (LSOTC), which represents interpretation of the influence on the distribution of craters shown by FDCC. TPC uniquely corresponds to the computation of TPD, whereas DCC depends on algorithms for computing the elevation of each crater according to the topography, center coordinates, and radius of impact crater, and FDCC relies on the architecture of the custom designed low-pass filter for filtering DCC. However, all variations of DCC and FDCC, which includes the various impact crater data sets, showed a correlation among the density of craters and elevation over 70–80% of the planet surface. Additionally, if we assume that the ocean primarily caused the noted correlation, LSOTC offers a mathematical approach for estimating topographic change of the ocean’s extent over time. Accordingly, TPD is the first new practical application of MTSP to lunar and planetary sciences, showing correlation of topography to a physical process.     

Bayesian network-based extraction of lunar impact craters from optical images and DEM data

Impact craters are among the most noticeable geomorphological features on the planetary surface and yield significant information about terrain evolution and the history of the solar system. Thus, the recognition of impact craters is an important branch of modern planetary studies. Aiming at addressing problems associated with the insufficient and inaccurate detection of lunar impact craters, a decision fusion method within the Bayesian network (BN) framework is developed in this paper to handle multi-source information from both optical images and associated digital elevation model (DEM) data. First, we implement the edge-based method for efficiently searching crater candidates which are the image patches that can potentially contain impact craters. Secondly, the multi-source representations of an impact crater derived from both optical images and DEM data are proposed and constructed to quantitatively describe the two-dimensional (2D) and three-dimensional (3D) morphology, consisting of Histogram of Oriented Gradient (HOG), Histogram of Multi-scale Slope (HMS) and Histogram of Multi-scale Aspect (HMA). Finally, a BN-based framework integrates the multi-source representations of impact craters, which can provide reductant and complementary information, for distinguishing craters from non-craters. To evaluate the effectiveness and robustness of the proposed method, experiments were conducted on three lunar scenes using both orthoimages from the Lunar Reconnaissance Orbiter (LRO) and DEM data acquired by the Lunar Orbiter Laser Altimeter (LOLA). Experimental results demonstrate that integrating optical images with DEM data significantly decreases the number of false positives compared with using optical images alone, with F₁-score of 84.8% on average. Moreover, compared with other existing fusion methods, our proposed method was quite advantageous especially for the detection of small-scale craters with diameters less than 1000 m.     

Integrated method for crater detection from topography and optical images and the new PH9224GT catalogue of Phobos impact craters

In a large majority of lunar and planetary surface images, impact craters are the most abundant geological features. Therefore, it is not surprising that crater detection algorithms (CDAs) are one of the most studied subjects of image processing and analysis in lunar and planetary science. In this work we are proposing an Integrated CDA, consisting of: (1) utilization of DEM (digital elevation map)-based CDA; (2) utilization of an optical-based CDA; (3) re-projection of used datasets and crater coordinates from normal to rotated view and back; (4) correction of the brightness and contrast of a used optical image; and (5) tile generation for the optical-based CDA and an assembling of results with an elimination of multiple detections, in combination with a pyramid approach down to the resolution of the available DEM image; and (6) a final integration of the results of DEM-based and optical-based CDAs, including a removal of duplicates. The proposed CDA is applied to one specific asteroid-like body, the small Martian moon Phobos. The experimental evaluation of the proposed CDA is done by a manual verification of crater-candidates and a search for uncatalogued craters. The evaluation has shown that the proposed CDA was used successfully for cataloging Phobos craters. The major result of this paper is the PH9224GT – currently the most complete global catalogue of the 9224 Phobos craters. The possible applications of the new catalogue are: (1) age estimations for any selected location; and (2) comparison/evaluation of the different chronology and production functions for Phobos. This confirms the practical applicability of the new Integrated CDA – an additional result of this paper, which can be used in order to considerably extend the current crater catalogues.     

Large-scale impact cratering on the terrestrial planets

Impact cratering as a geologic process on the terrestrial planets is addressed. The crater densities on the Earth and Moon form the basis for a standard flux-time curve, which can be used to date unsampled planetary surfaces and constrain the temporal history of endogenic geologic processes. The attached uncertainties and the shape of the flux curve (a rapid exponential decay for the period 4.6 – 4.0 by, followed by the establishment of a constant fluid by 3.5 – 3.0 by which continues more or less to the present) are such that only very old (3.8 by) and very young ( 1.0 by) surfaces can be dated with some confidence. Dating of intermediate-aged surfaces is more imprecise; a problem which is most significant for the geologic history of Mars.

The cratering mechanics of simple craters are fairly well understood. A transient cavity of roughly parabolic cross-section results from the combined excavation and displacement of the target rocks by the cratering flow-field, which can be approximated by the Z-model derived from shallow-buried explosive events. The walls of the transient crater are unstable and slump inwards, resulting in a final bowl-shaped crater partially filled by breccia. The formation process of larger, shallow complex structures is less well understood. Recent models favor the complete collapse of the initial cavity, with the dynamic uplift of the excavated cavity floor. Regardless of the driving force for uplift, yield strength of the target rocks must be drastically reduced during cavity modification by an, as yet, imprecisely known process.

The formation of large impact basins had a profound effect on planetary evolution. They define the basic tectonic and stratigraphic framework of the Moon and their secondary effects lasted for 10⁸ y. The evidence is less compelling from other planets, but a general feature appears to be the concentration of later endogenic activity in and around basins. On Earth, it is possible that basin-formation contributed to the establishment of the dichotomy between proto-continental and proto-oceanic crusts. The effects of impact continue into recent geologic history and may be linked to major biological changes on Earth, such as at the Cretaceous-Tertiary boundary.     

火星探测直接转移轨道精确求解研究

针对火星探测直接转移轨道精确求解问题, 提出了一种快速微分修正算法. 基于二体模型建立控制参数和目标参数偏差关系的数学模型, 并由此求解系统的偏导数矩阵; 采用B平面参数作为中间变量, 对算法进行两层迭代设计, 有效地减少了求解过程中的积分运算次数. 以2018年火星探测机会为例对算法进行了验证, 仿真结果表明, 利用圆锥曲线拼接法得到的轨道初值, 求解一条标准轨道只需6~9次积分迭代. 通过STK对计算结果进行了对比和验证.