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。     

月球撞击闪光观测研究进展

月球撞击闪光是流星体撞击月球表面产生的闪光现象,回顾了20年来月球撞击闪光观测的研究进展,介绍了美国航空航天局(NASA)、欧洲航天局(ESA)和西班牙的团队开展的监测计划,说明各计划对观测技术、数据处理和分析技术的贡献,并总结了主要的观测和研究成果。利用长期积累的观测数据已经能够对撞击体的大小分布和流量提供一定的限制,但由于存在观测数据有限和撞击模型粗糙等问题,因此必须对它们进行改进。中国在月球撞击闪光观测方面的研究还是空白,建议开展地基和针对月球背面的监测计划,为中国的探月工程和载人登月计划提供相关设施防护的设计依据。     

地基雷达技术及其在太阳系天体探测中的应用

人类利用雷达波进行天文研究距今已有40多年历史了.它是一种发射雷达波到目标天体,通过分析其回波特性来进行天文探测的技术.该文从地基雷达在太阳系天体探测中的应用出发,分析了地基雷达相比其他探测手段的优点;介绍了地基雷达的基本工作原理;给出了近年来地基雷达的发展情况和探测成果;最后从现有条件出发,探讨了我国开展地基雷达探测的设想.     

1998—1999年国际狮子座流星雨观测研究评述

1998－1999年的狮子座流星雨观测研究取得了十分丰富的成果，概要介绍了在此期间目视观测，雷达观测，航空观测，气球观测，卫星安全检测星撞击月球和月球钠尾观测方面取得的成果和进展。     

雷达探测技术在探月中的应用

人类运用雷达探测技术对月球探测取得了丰硕的科学成果,开展了对月球地形地貌探测、月壤厚度反演、月球次表层结构探测、月球水冰探测等研究。以不同的探测方式和科学目的综述了国内外运用雷达探测技术对月球探测所取得的一系列科学成果,以及我国成功发射"嫦娥三号"卫星,其巡视器"玉兔号"上搭载的测月雷达(Lunar Penetration Radar)将用于探测月球次表层结构和月壤厚度与结构,同时也介绍了测月雷达的基本原理与一些基本指标参数。     

表层穿透雷达在月球和深空探测中的应用

对月球以及更远天体或者空间环境的探测是人类航天活动的重要方向。开展月球和深空探测有利于研究太阳系起源、演化与现状,以及生命起源与演变等重大科学问题,有利于催生基础性、前瞻性的学科与技术。相比光学探测方法,雷达具有强穿透性、极化特性以及不受光照限制等优势,是探测天体特性的有效手段之一,在月球和深空探测中发挥了重要作用。电磁波能够穿透几米到几千米的次表层,可用于探测月球和深空目标的表层介电常数、次表层结构、电离层及水冰等。按照探测方式的不同,表层穿透雷达探测主要包括地基雷达、环绕器雷达及巡视器雷达3种方式。针对不同的科学目标,不同的探测方式具有各自的优势和不足。回顾了表层穿透雷达在月球、火星以及小行星等探测中的科学应用,总结了已经投入使用以及计划中的各种雷达科学载荷的探测任务、参数设计、工作原理和探测结果,展望了在未来利用表层穿透雷达进行月球和深空探测的发展趋势。     

潜在的500MHz雷达网及其应用

随着曲靖500 MHz非相干散射雷达的初步建成并投入使用,利用其开展雷达天文学的研究成为可能。基于雷达方程,假定曲靖雷达发射信号,分析了现有昆明40 m天线、密云50 m天线和贵州500 m射电望远镜作为接收器接收回波信号,构建潜在雷达网进行天文测量的能力,报道了探测空间碎片的初步成果,探讨了我国开展地基雷达观测近地小行星的设想。最后呼吁我国开展地基雷达和VLBI联合进行太阳系天体探测,开拓深空领域。     

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。     

空间目标的地基红外观测研究进展

作为一个新兴的研究方向,空间目标的地基红外观测能够与传统雷达和光学观测形成互补,完善空间监测机制。红外具有宽阔的波段范围和特有的热辐射波段,在光谱分析和白天观测方面蕴藏着更大的发展潜力。近年来美国开始征用大型的红外望远镜,或者通过改造光学望远镜,研究空间目标在红外波段的特性。综述了参与空间目标地基红外观测的望远镜工作状况,以及近10年来空间目标监测在红外巡天、白天观测、测光和光谱分析方面的研究进展,最后对空间目标的地基红外观测研究进行总结与展望。     

空间碎片地基雷达探测综述

分析了空间碎片地基雷达探测的必要性和现实意义,介绍了国外有代表性的地基雷达工作概况,在此基础上,给出了描述空间碎片的轨道参量和物理参量,并对空间碎片地基雷达探测所需的关键技术进行了探讨。     

Determination of spacecraft and phobos parameters of motion in the Phobos-Grunt project

For the needs of the upcoming flight to Phobos within the framework of the project Phobos-Grunt, a dynamical numerical theory of the motion of Phobos is developed on the basis of Earth-based and spacecraft (SC) optical measurements and Earth-based radio observations of the SC motion. The theory uses the most reliable astronomical constants. Within the framework of a unified dynamical model, an algorithm is proposed for the joint correction of Phobos and the spacecraft parameters of motion, among which are the secular acceleration of Phobos and its gravitational constant. The accuracy of the obtained ephemeris is estimated for the time of the SC arrival to Phobos.     

Space-based aperture array for ultra-long wavelength radio astronomy

The past decade has seen the advent of various radio astronomy arrays, particularly for low-frequency observations below 100 MHz. These developments have been primarily driven by interesting and fundamental scientific questions, such as studying the dark ages and epoch of re-ionization, by detecting the highly red-shifted 21 cm line emission. However, Earth-based radio astronomy observations at frequencies below 30 MHz are severely restricted due to man-made interference, ionospheric distortion and almost complete non-transparency of the ionosphere below 10 MHz. Therefore, this narrow spectral band remains possibly the last unexplored frequency range in radio astronomy. A straightforward solution to study the universe at these frequencies is to deploy a space-based antenna array far away from Earths’ ionosphere. In the past, such space-based radio astronomy studies were principally limited by technology and computing resources, however current processing and communication trends indicate otherwise. Furthermore, successful space-based missions which mapped the sky in this frequency regime, such as the lunar orbiter RAE-2, were restricted by very poor spatial resolution. Recently concluded studies, such as DARIS (Disturbuted Aperture Array for Radio Astronomy In Space) have shown the ready feasibility of a 9 satellite constellation using off the shelf components. The aim of this article is to discuss the current trends and technologies towards the feasibility of a space-based aperture array for astronomical observations in the Ultra-Long Wavelength (ULW) regime of greater than 10 m i.e., below 30 MHz. We briefly present the achievable science cases, and discuss the system design for selected scenarios such as extra-galactic surveys. An extensive discussion is presented on various sub-systems of the potential satellite array, such as radio astronomical antenna design, the on-board signal processing, communication architectures and joint space-time estimation of the satellite network. In light of a scalable array and to avert single point of failure, we propose both centralized and distributed solutions for the ULW space-based array. We highlight the benefits of various deployment locations and summarize the technological challenges for future space-based radio arrays.     

Radar observations of the asteroid 2011 UW158

In July 2015 intercontinental bistatic radar observations of the potentially dangerous asteroid 2011 UW158 during its close approach to the Earth were carried out. The asteroid was illuminated at a frequency of 8.4 GHz with the 70-m DSS-14 antenna of the Goldstone Deep Space Communications Complex, while the signal reflected from the asteroid was received with the 32-m radio telescopes of the Quasar VLBI network at the Zelenchukskaya and Badary Observatories. The spectra of the reflected radio signals were obtained. The sizes and rotation period of the asteroid consistent with photometric observations and the ratio of the powers of the reflected signals with left- and right-hand circular polarizations were determined. The derived values suggest that the asteroid has an inhomogeneous surface and a prolate shape. The observations of the Doppler shift of the reflected signal frequency were obtained, which allowed the orbital parameters of the asteroid to be improved.     

A review of earth-based radar mapping of the moon

Lunar radar mappings carried out in the late 1960's and 1970's have provided several valuable insights into lunar surface processes. These radar mappings used the delay-Doppler technique developed by Gordon Pettengill and his colleagues. These radar mappings also needed the narrow antenna beams, now available with large radio telescopes such as those at the Arecibo and Haystack Observatories. Two-element radar interferometers have provided resolution of the delay-Doppler ambiguity at meter wavelengths and provided topographic information at centimeter wavelengths. These techniques have provided high-resolution lunar radar-maps at 3.8-cm, 70-cm, and 7.5-m wavelengths, a set of wavelengths which span the window available for Earth-based radar mapping of the Moon.These radar maps have been used along with other Earth-based and Apollo orbital measurements to define surface units. The radar maps and these other data can describe physical properties such as small-scale (centimeter sized) blockiness and surface chemistry (titanium and iron) content. These estimates of lunar surface properties rely heavily upon extrapolation of surface sampling results.Presented at the IAU-COSPAR Julian Schmidt Symposium on 100 Years of Lunar Mapping held at Lagonissi, Greece, 25–27 May, 1978.     

Investigation of LO-Coupled Noise for a Sideband Separation Superconducting SIS Receiver

The Superconducting Superconductor-Insulator-Superconductor (SIS) receivers have become the preferred method for (sub)millimeter-wave radio astronomical observations due to the extremely low receiver noise temperature. The coupling noise of the local oscillator (LO) system is also a part of the receiver noise. In many years of astronomical observations, it is found that the LO-coupled noise cannot be completely ignored, which has a certain impact on the sensitivity of astronomical observations. The noise temperature of the superconducting SIS receiver was tested using two different kinds of signal generators as the primary signal source of the LO system. It is found that the base noise output by the signal generator can be coupled into the receiver to increase the receiver noise. By adding a narrow band filter to the output of the signal generator, the base noise of the signal generator can be filtered out, and this part noise of the receiver can be eliminated, the overall noise of the receiver is reduced, and the sensitivity of the telescope is improved.     

边带分离型超导SIS接收机本振耦合噪声研究

超导SIS (Superconductor-Insulator-Superconductor)接收机因极低的接收机噪声温度成为毫米波和亚毫米波段射电天文观测的首选.本振系统耦合噪声也是接收机噪声的一部分,在多年的天文观测中,发现本振耦合噪声无法完全忽略,对天文观测的灵敏度有一定影响.采用两个不同种类的信号发生器作为本振系统初级信号源,测试了超导SIS接收机的噪声温度,发现信号发生器输出的基底噪声能够耦合到接收机内部,从而增加接收机噪声强度.分析研究了本振系统热噪声和信号发生器基底噪声对接收机噪声的影响.通过在信号发生器输入端加入窄带滤波器滤除其基底噪声,消除了信号发生器基底噪声引入的接收机噪声,降低了接收机的整体噪声,提高了望远镜的灵敏度.     

Frequency selective surfaces for radio astronomy

Frequency selective surfaces (FSSs) with the Jerusalem-cross array configuration have been developed for simultaneous observations of radio astronomical sources at the 40GHz and 80GHz bands. For supporting material, PET(polyethylene terephthalate: 200×220mm large, 12m thick, permittivity 3.0) was used, and copper was used for the conducting array. The measured characteristics were in good agreement with the calculated ones. The fabricated FSS has low insertion losses of less than 0.2dB and little distortion of polarization for each band. The characteristics of the developed FSS satisfy radio astronomical requirements.     

射电干涉测量对天文脉泽研究的贡献

天文脉泽已成为一个迅速的研究领域，重点评述了射电干涉测量对天文脉泽观测和研究所起的作用。     

The initial train radius of sporadic meteors

The height distributions, velocity distributions and flux measurements of underdense echoes determined from meteor radar observations are significantly affected by the attenuation associated with the initial radius of meteor trains. Dual-frequency radar observations of a very large set of sporadic radar meteors at 29 and 38 MHz yield estimates of the initial train radius and its dependence on height and meteoroid speed as determined by the time-delay method. We provide empirical formulae that can be used to correct meteoroid fluxes for the effect of initial train radius at other radio frequencies.     

云南天文台40米射电望远镜河外射电源观测

为了在云南天文台40 m天线上开展射电天文研究,使用它进行了河外射电源流量试观测。通过对河外致密源进行ON/OFF跟踪观测,得到射电源的流量变化曲线。但数据质量并不理想,说明系统存在一些问题。随后,根据对该望远镜系统的稳定性及其无线电环境干扰现状的考察,以及对现存问题的分析,提出了相应的解决方法。