月球亮温度的射电多波段地基观测

月球是距离地球最近的天体,人类对它的研究探索一直没有停止。月球不仅反射可见光,还在红外和微波频段遵循热辐射机制辐射能量。亮温度是反映微波特性的一个重要指标。由月球亮温度,可以进行月壤特性的研究,从而进一步分析月球表层及近表层结构和物质组成。另外月球亮温度也是影响月球探测器星地链路的一个重要因素。从月球的亮温度出发,阐述了月球射电辐射机制;并对地基射电望远镜的多波段观测进行总结,分别从设备、方法、结果等方面给出月球亮温度观测的发展;最后对我国地基射电望远镜对月球亮温度的观测进行了介绍。     

基于测月雷达机制月壤相对介电常数反演方法模拟研究

嫦娥三号卫星于2013年12月2日发射,并成功着陆月球,其巡视器上搭载的测月雷达实现了首次雷达就位探测月球。基于测月雷达的探测机制,给出了两种计算月壤相对介电常数的方法,标定件标定法和双天线时延法,并通过仿真验证了两种计算方法的有效性,文中同时给出了两种计算方法存在的局限性,为后期基于嫦娥三号雷达数据进行月球次表层的介电特性反演提供了重要依据。     

基于最大熵谱估计的高能电子周期特性研究

利用最大熵谱法研究了风云二号D星≥2.0 MeV的高能电子通量的周期特性,算法以自相关模型为基础,通过对最大熵谱功率谱的分析,推测出风云二号D星高能电子通量存在13.87 d和27.8 d的周期.根据最终预报误差准则(Final Prediction Error,FPE)和赤池信息量准则(Akaike Informat...     

电离层掩星反演的正则最大熵法

电离层掩星数据现已成为电离层观测数据的重要来源,对掩星数据的反演研究一直是掩星研究的热点.传统采用的改正TEC(1btal Electron Content)的Abel变换反演法为线性反演法,它会把测量误差带入反演结果中.为改善反演效果受测量误差的影响,引入两种非线性的反演方法一正则化和正则最大熵反演法.随后设计模拟试验,对3种方法进行验证、比较,得到正则最大熵反演法可以很好地减小测量误差的影响.     

Maximum Entropy Regularization Method of Ionospheric Occultation

With the increasing of applications of Global Positioning System (GPS), the research on the factors affecting the radio signals is becoming more and more important. One of the most significant effects on ionosphere monitoring is the ionospheric radio occultation (IRO), and the IRO data is now serving as one of the most important monitoring sources for the ionospheric measurements. Meanwhile the inversion of the occultation data is a popular topic. The traditional Abel inversion process through compensated total electron content (TEC) is a linear inversion method, thus it would transfer the measurement errors directly to the inversion results. In order to improve the occultation results, we introduce in this paper two nonlinear methods, namely the regularization method and the maximum entropy regularization method. Through designed simulative experiments, we verify and compare these three methods, and conclude that the maximum entropy regularization method can reduce significantly the influence of measurement errors.     

Photometric Stability of the Lunar Surface

The rate at which cratering events currently occur on the Moon is considered in light of their influence on the use of the Moon as a radiometric standard. The radiometric effect of small impact events is determined empirically from the study of Clementine images. Events that would change the integral brightness of the moon by 1% are expected once per 1.4 Gyr. Events that cause a 1% shift in one pixel for low Earth-orbiting instruments with a 1-km nadir field of view are expected approximately once each 43 Myr. Events discernible at 1% radiometric resolution with a 5 arc-sec telescope resolution correspond to crater diameters of approximately 210 m and are expected once every 200 years. These rates are uncertain by a factor of two. For a fixed illumination and observation geometry, the Moon can be considered photometrically stable to 1 × 10⁻⁸per annum for irradiance, and 1 × 10⁻⁷per annum for radiance at a resolution common for spacecraft imaging instruments, exceeding reasonable instrument goals by six orders of magnitude.     

A Study of the Lunar Soil in Regions with Temperature Anomalies

Based on a large body of observational data on radio emission from the Moon, we study the dependence of lunar radio temperature variations on illumination conditions. The data were obtained with the RATAN-600 radio telescope with a high sensitivity and resolution, which has not yet been used to construct radio images of the Moon. The harmonic parameters (amplitudes and phase angles) were determined both for the average Moon and for regions with temperature anomalies revealed by the RATAN-600 observations. These parameters allow the physical properties of the lunar soil to be investigated. The distribution of the loss-angle tangent (tan ), one of the characteristics of the lunar material, over the Moon was determined. The loss-angle tangent is related to the content of ilmenite, a rock containing oxygen, iron, and titanium, in the lunar soil. Studies of the ilmenite distribution on the Moon are particularly important in view of the prospects for building a habitable lunar base that needs oxygen. It is relatively easy and cheap to extract oxygen, iron, and titanium from ilmenite.     

Measurements of the Quiet-Sun Level Brightness Temperature at 8 mm

Defining the solar brightness temperature accurately at millimeter wavelengths has always been challenging. One of the main reasons has been the lack of a proper calibration source. New Moon was used earlier as a calibration source. We carried out a new extensive set of observations at 8 mm using the New Moon for calibration. The solar and Moon observations were made using the 14-meter radiotelescope operated by the Aalto University Metsähovi Radio Observatory in Finland. In this article, we present our method for defining the brightness temperature of the quiet-Sun level (QSL). Based on these observations, we found \(8100~\mbox{K} \pm 300~\mbox{K}\) to be the mean value for the QSL temperature. This value is between the values that were reported in earlier studies.     

The Area of Cold Traps on the Lunar Surface

We numerically calculate the probability and area of permanent shadowing as a function of the selenographic latitude as well as the total area of the permanently shadowed surface for various hierarchical models of the lunar surface. The permanently shadowed area is shown to rapidly increase with increasing number of hierarchical surface levels. For a two-level model of the lunar relief, where the surface of craters is complicated by a random small-scale relief with a Gaussian distribution of heights and slopes, the area of the doubly shadowed regions of the lunar surface is approximately an order of magnitude smaller than the area of the singly shadowed regions. A comparison of the permanently shadowed area calculated by using averaged statistical relations and data on the actual distribution of craters near the lunar poles shows almost complete agreement.     

Estimation of the Area of the Perpetually Shaded Lunar Surface

We present the results of computer simulation of the shadowing effect for three types of surface: (1) cratered, (2) formed by a random profile with Gaussian statistical height and slope distributions, and (3) a two-scale surface representing a cratered area that is complicated by small-scale random relief. The calculations are based on data on the distribution of lunar craters derived from the diameter/depth ratio and on the assumption of the equilibrium distribution of the crater population in the circumpolar areas of the lunar surface. We determined the characteristics of perpetually shaded areas of the lunar surface: the probability of the constant shadowing of an arbitrary surface point, the fraction of the perpetually shaded area as a function of selenographic latitude, the latitudinal dependence of the perpetually shaded area, and the total area of the perpetually shaded surface. The calculations showed that the presence of structural features of different scale on the lunar surface can considerably increase the estimate of the fraction of the perpetually shaded area compared to existing estimates.     

Integration and Comparison of Clementine and Lunar Prospector Data: Global Scale Multielement Analysis1 (Fe,Ti, and Th) of the Lunar Surface

In this paper, we present (1) a statistical analysis, based on a systematic clustering method, of a dataset integrating the global abundance maps of the three elements iron, titanium, and thorium derived from Clementine and Lunar Prospector and (2) a comparison of iron abundances between Clementine and Lunar Prospector. Homogeneous geologic units are compositionally characterized and spatially defined in relation to the major rock types sampled on the Moon. With the lowest abundances of Fe, Ti, and Th found on the Moon, the lunar highland terrains are quite homogeneous with two major large feldspathic units, one being slightly more mafic than the other. Two distinct regions with unique compositions are unambiguously identified: the Procellarum KREEP Terrane (PKT) and the South Pole–Aitken (SPA). The PKT, which includes all the units with Th abundances higher than 3.5 ppm (KREEP-rich materials), is delimited by an almost continuous ringlike unit. In particular, it includes the western nearside maria, except for Mare Humorum. With concentrations in Fe, Ti, and Th enhanced relative to the surrounding highlands, the South Pole–Aitken basin floor represents a large mafic anomaly on the far side, suggesting wide deposits of lower crust and possible mantle materials. However, due to indirect residual latitude effects in the CSR (Clementine spectral reflectance) measurements, iron abundances might have been overestimated in SPA, thus implying that crustal materials, rather than mantle materials, might represent the dominant contributor to the mafic component exposed on the basin floor.     

The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm

The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the absolute solar brightness temperature. We tune the superconductor–insulator–superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the absolute brightness temperature of the Sun. The derived solar brightness temperature is \(7700 \pm 310~\mbox{K}\) at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the absolute temperature scale that is lacking from interferometer observations.     

天文成像数值仿真的相位屏模拟方法

通过利用Monte—Carlo方法对湍流相位屏模拟进行验证和分析。给出加入次谐低频补偿相位屏与直接谱反演相位屏的对比结果,并分析了在考虑内外尺度时次谐低频补偿方法的有效性。此外,给出了基于天文观测的多相位屏的湍流分层模型。在此基础上对天文成像进行数值仿真,并给出了仿真结果。