宽带频谱序列干扰信号识别与统计方法

随着科学技术的不断进步,射电天文台站趋于自动化,各类电子设备的广泛使用使得射电天文台站的电磁环境变得尤为复杂,如何有效识别和统计复杂频谱中的干扰信号是当前射电天文台站亟需解决的问题,故提出一种宽带频谱序列干扰信号识别与统计方法.首先,对每组宽带频谱进行信噪分离、识别频谱中的干扰信号;然后,对第1组宽带频谱信号识别结果及信号特征建立模板库,后续每组频谱的信号识别结果与模板库中对应频率的信号进行相似性分析,根据相似性分析结果,统计信号次数,更新模板库;实现宽带频谱序列干扰信号的识别与统计.针对QTT (QiTai Radio Telescope)台站实测频谱,运用该方法进行干扰信号识别与统计,能够有效识别并标记频谱中的干扰信号,并统计干扰信号随时间、方向的变化趋势.     

太阳米波和分米波Ⅱ型、Ⅲ型射电暴及其精细结构观测研究进展

太阳米波和分米波的射电观测是对太阳爆发过程中耀斑和日冕物质抛射现象研究的重要观测手段。米波和分米波的太阳射电暴以相干等离子体辐射为主导,表现出在时域和频域的多样性和复杂性。其中Ⅱ型射电暴是激波在日冕中运动引起电磁波辐射的结果。在Ⅱ型射电暴方面,首先对米波Ⅱ型射电暴的激波起源问题和米波Ⅱ型射电暴与行星际Ⅱ型射电暴的关系问题进行了讨论;其次,结合Lin-Forbes太阳爆发理论模型对Ⅱ型射电暴的开始时间和起始频率进行讨论:最后,对Ⅱ型射电暴信号中包含的两种射电精细结构,Herringbone结构(即鱼骨结构)和与激波相关的Ⅲ型射电暴也分别进行了讨论。Ⅲ型射电暴是高能电子束在日冕中运动产生电磁波辐射的结果。在Ⅲ型射电暴方面,首先介绍了利用Ⅲ型射电暴对日冕磁场位形和等离子体密度进行研究的具体方法;其次,对利用Ⅲ型射电暴测量日冕温度的最新理论进行介绍;最后,对Ⅲ型射电暴和Ⅱ型射电暴的时间关系、Ⅲ型射电暴和粒子加速以及Ⅲ型射电暴信号中包含的射电精细结构(例如斑马纹、纤维爆发及尖峰辐射)等问题进行讨论并介绍有关的最新研究进展。     

太阳射电高时间分辨率观测中的抗干扰措施

本文针对太阳射电高时间分辨率观测研究中普遍关心的事件证认问题，分析了精细结构事件与干扰信号在“空域”和“频域”上的特征差异，在“１０ｃｍ波段高时间分辨率太阳强度纹”上，采取了抗干扰和识别干扰的技术措施，极大的抑制了雷达干扰，提高了事件的置信度。在缺乏不同地域精细结构同时性事件情况下，本文介绍的措施，对事件的自证认不失为一种有效的手段。     

Unusual Solar Radio Burst Observed at Decameter Wavelengths

An unusual solar burst was observed simultaneously by two decameter radio telescopes UTR-2 (Kharkov, Ukraine) and URAN-2 (Poltava, Ukraine) on 3 June 2011 in the frequency range of 16?–?28 MHz. The observed radio burst had some unusual properties, which are not typical for the other types of solar radio bursts. Its frequency drift rate was positive (about 500 kHz?s^?1) at frequencies higher than 22 MHz and negative (100 kHz?s^?1) at lower frequencies. The full duration of this event varied from 50 s up to 80 s, depending on the frequency. The maximum radio flux of the unusual burst reached ≈10³ s.f.u. and its polarization did not exceed 10 %. This burst had a fine frequency-time structure of unusual appearance. It consisted of stripes with the frequency bandwidth 300?–?400 kHz. We consider that several accompanied radio and optical events observed by SOHO and STEREO spacecraft were possibly associated with the reported radio burst. A model that may interpret the observed unusual solar radio burst is proposed.     

关于太阳射电快速活动真伪信号识别问题

本文列举了云南天文台四波段太阳射电实测中得到的几种干扰实例及确认的太阳快速信号，在认识到太阳射电和干扰信号十分相似的基础上，探讨如何识别真伪信号问题。     

A Highly Circularly Polarized Solar Radio Emission Component Observed at Hectometric Wavelengths

We report here the observation of a rare solar radio event at hectometric wavelengths that was characterized by essentially 100% circularly polarized radiation and that was observed continuously for about six days, from May 17 to 23, 2002. This was the first time that a solar source with significantly polarized radiation was detected by the WAVES experiment on the Wind spacecraft. From May 19 to 22, the intense polarized radio emissions were characterized by quasi-periodic intensity variations with periods from one to two hours and with superposed drifting, narrowband, fine structures. The bandwidth of this radiation extended from about 400 kHz to 7 MHz, and the peak frequency of the frequency spectrum slowly decreased from 2 MHz to about 0.8 MHz over the course of four days. The radio source, at each frequency, was observed to slowly drift from east to west about the Sun, as viewed from the Earth and was estimated to lie between 26 and 82R_⊙ (R_⊙ = 696 000 km). We speculate that this unusual event may represent an interplanetary manifestation of a moving type IV burst and discuss possible radio emission mechanisms. The ISEE-3 spacecraft may possibly have detected a similar event some 26 years ago.     

Formation of zebra patterns of solar microwave bursts as a result of propagation of radio waves through the inhomogeneous corona

The geoefficiency of solar bursts is diagnosed using the dynamic radio emission spectrum. At certain time intervals, the spectrum exhibits nearly parallel narrow-band emission strips termed the zebra pattern. Although there are many hypotheses of its origin, all of them do not take into account changes in the signal parameters upon signal propagation through the solar corona. Our analysis shows that the propagation effects form a dynamic spectrum that contains a zebra pattern. The properties of the modeled spectrum are shown to coincide with the basic properties of the observed spectrum. It is clarified that the spike structure of strips is a natural consequence of the interference of radio waves, and the occurrence of this structure is considered to be evidence in favor of the interference nature of the zebra pattern formation. Consequently, the zebra pattern can be formed not in the radiation source itself, but rather can arise as a result of propagation of radio waves through an inhomogeneous refracting medium of the solar corona.     

Scaling-laws of Radio Spike Bursts and Their Constraints on New Solar Radio Telescopestwo

Radio observation is one of important methods in solar physics and space science. Sometimes, it is almost the sole approach to observe the physical processes such as the acceleration, emission, and propagation of non-thermal energetic particles, etc. So far, more than 100 solar radio telescopes have been built in the world, including solar radiometers, dynamic spectrometers, and radioheliographs. Some of them have been closed after the fulfillment of their primary scientific objectives, or for their malfunctions, and thus replaced by other advanced instruments. At the same time, based on some new technologies and scientific ideas, various kinds of new and much more complicated solar radio telescopes are being constructed by solar radio astronomers and space scientists, such as the American E-OVSA and the solar radio observing system under the framework of Chinese Meridian Project II, etc. When we plan to develop a new solar radio telescope, it is crucial to design the most suitable technical parameters, e.g., the observing frequency range and bandwidth, temporal resolution, frequency resolution, spatial resolution, polarization degree, and dynamic range. Then, how do we select a rational set of these parameters? The long-term observation and study revealed that a large strong solar radio burst is frequently composed of a series of small bursts with different time scales. Among them, the radio spike burst is the smallest one with the shortest lifetime, the narrowest bandwidth, and the smallest source region. Solar radio spikes are considered to be related to a single magnetic energy release process, and can be regarded as an elementary burst in solar flares. It is a basic requirement for the new solar radio telescope to observe and discriminate these solar radio spike bursts, even though the temporal and spatial scales of radio spike bursts actually vary with the observing frequency. This paper presents the scaling laws of the lifetime and bandwidth of solar radio spike bursts with respect to the observing frequency, which provide some constraints for the new solar radio telescopes, and help us to select the rational telescope parameters. Besides, we propose a spectrum-image combination mode as the best observation mode for the next-generation solar radio telescopes with high temporal, spectral, and spatial resolutions, which may have an important significance for revealing the physical essence of the various non-thermal processes in violent solar eruptions.     

Determination of the coronal magnetic field and the radio-emitting electron energy from a Type IV solar radio burst

The intensity and frequency spectrum of gyro-synchrotron emission from energetic solar electrons radiating in coronal magnetic fields are calculated. These calculations, based on a recent study of the generation of gyro-synchrotron emission in a magnetoactive plasma, are applied to a Type IV radio burst originating at a high altitude in the solar corona. It is shown that the observed frequency spectrum of the burst, which exhibits very sharp low and high frequency cutoffs, can be best understood in terms of gyro-synchrotron emission in an ionized medium and that from the observed frequency spectrum and the ambient coronal density it is possible to deduce both the magnetic field at the site of the emission and the range of electron energies responsible for the burst.NAS-NASA Post-Doctoral Resident Research Associate.Research supported by the National Research Foundation under grant GP-849.     

Positively Drifting Structures During the 18 March 2003 Solar Flare

We analyze the high-frequency drift radio structures observed by the spectrometer at Purple Mountain Observatory (PMO) over the frequency range of 4.5 – 7.5 GHz during the 18 March 2003 solar flare. The drifting structures take place before the soft X-ray maximum, almost at the maximum of hard X-ray flux at 25 – 50 keV. For the first time, the positive drift in this kind of radio structures is detected in such a high frequency range. Their global drifting rate is roughly estimated as 3.6 GHz s⁻¹. They appear in four groups, lasting in total for less than 6 s, and have a broad bandwidth of more than 2 GHz but a smaller ratio of the bandwidth of the drifting structures to mean frequency than that of the lower frequency range. The lifetime of each individual burst in this event can be derived by using the high temporal resolution of the spectrometer at PMO and has an average value of 36.3 ms. Since the negative drifting structures observed in the 0.6 – 4.5 GHz frequency range were interpreted to be a radio signature of a plasmoid ejected upward (moving out of the Sun), the present observation may imply that it is possible for a plasmoid to move downward during a solar flare. However, for a confirmation of this suggestion direct radio imaging observation would be needed.     

Analysis of spike emission data at 2545/2645 MHz in the peak year of the 22nd solar cycle

We briefly discuss the observed features including the high flux density, short duration, narrow emission band, fast frequency drift, quasi-periodic oscillation and fast variation of polarized components, of 51 spike emission events observed at 2545/2645 MHz in the solar activity peak year, 1991 January–December, and carry out correlation analysis between these events and optical flares, magnetic field intensity and configuration of flare regions, and sunspot evolution types of active regions. In view of the fact that the observed and statistical characteristics of the spike emissions are very different from those of known types of solar radio burst and known solar radio components, we think that the spike emission in the peak years is probably a new type of radio burst excited by electron cyclotron maser instability under wave-particle resonance, or a new solar radio component.     

Radio frequency interference mitigation using pseudoinverse learning autoencoders

Radio frequency interference(RFI) is an important challenge in radio astronomy. RFI comes from various sources and increasingly impacts astronomical observation as telescopes become more sensitive. In this study, we propose a fast and effective method for removing RFI in pulsar data. We use pseudo-inverse learning to train a single hidden layer auto-encoder(AE). We demonstrate that the AE can quickly learn the RFI signatures and then remove them from fast-sampled spectra, leaving real pulsar signals. This method has the advantage over traditional threshold-based filter method in that it does not completely remove contaminated channels, which could also contain useful astronomical information.     

The U-shaped spectrum of radio burusts and the spectrum of proton events

The theoretical explanation of the U-shape spectrum of Type IV solar radio bursts given in /1/ led us to expect certain correlations between this spectrum and that of the associated proton events. These correlations are established using Earth-based and space observations during the last solar cycle. They may be used for real-time prediction of proton events.     

明安图射电频谱日像仪图像的强度定标方法

明安图射电频谱日像仪(Mingantu Spectral Radioheliograph, MUSER)能够在0.4--15GHz超宽频带内实现高时间、高空间、高频率分辨率的太阳射电成像. 而射电亮温度是描述太阳物理过程的一个重要的参数, 在研究不同射电辐射机制、太阳磁场以及太阳爆发过程中非热粒子加速等问题上有着非常重要的作用, 因此必须对MUSER观测的图像进行亮温度定标. 将介绍一种适用于射电日像仪图像强度定标的方法. 太阳射电图像中包含着太阳圆盘的结构信息, 利用射电日像仪短基线的可视度函数拟合第一类贝塞尔函数, 可以得到图像中宁静太阳圆盘的射电半径和强度, 再利用瑞利-金斯定律和每天的太阳射电流量可以计算得到每天图像的定标因子$G_c$, 从而实现对MUSER图像强度的定标. 将该方法应用到MUSER的实际观测数据中, 包括宁静太阳和有太阳射电爆发等不同的情况, $G_c$的误差基本不超过10%, 得到的宁静太阳亮温度与其他宁静太阳的结果具有较高的相关性, 表明了此方法的可行性和有效性.     

Analysis of radio astronomy bands using CALLISTO spectrometer at Malaysia-UKM station

The e-CALLISTO system is a worldwide network that aims to observe solar radio emission for astronomical science. CALLISTO instruments have been deployed worldwide in various locations that together can provide continuous observation of the solar radio spectrum for 24 h per day year-round. Malaysia-UKM is a strategic equatorial location and can observe the Sun 12 h per day. This paper gives an overview of the spectrum allocation for radio astronomy, which falls in the specified operating frequency band of the CALLISTO spectrometer. The radio astronomy bands are analyzed at the Malaysia-UKM station according to the International Telecommunication Union recommendations. Some observational results are also presented in this paper.     

Harmonic structure of type IIIb and III bursts

A decameter solar radio storm of type IIIb and III bursts has been analysed, using single frequency records at frequencies 12.5 and 25.0 MHz.Several kinds of burst associations are classified. As a result it is shown that in double oblique burst-traces of type IIIb + III on the frequency-time plane the type III burst is shifted by an octave above the type IIIb burst at any moment of the IIIb + III pair's lifetime. In particular, the harmonic structure of the spectrum is peculiar to the event of type IIIb + III in the initial and the final stages. This property of the pair is clear if the type IIIb and III radiations occur at the fundamental coronal plasma frequency and its harmonic respectively. On the other hand, if it is assumed that a type IIIb burst is the precursor of a type III one, there is no reason why the two bursts should be harmonically related.     

Fast radio burst search: cross spectrum vs. auto spectrum method

The search for fast radio bursts(FRBs) is a hot topic in current radio astronomy studies. In this work, we carry out a single pulse search with a very long baseline interferometry(VLBI) pulsar observation data set using both auto spectrum and cross spectrum search methods. The cross spectrum method,first proposed in Liu et al., maximizes the signal power by fully utilizing the fringe phase information of the baseline cross spectrum. The auto spectrum search method is based on the popular pulsar software package PRESTO, which extracts single pulses from the auto spectrum of each station. According to our comparison, the cross spectrum method is able to enhance the signal power and therefore extract single pulses from data contaminated by high levels of radio frequency interference(RFI), which makes it possible to carry out a search for FRBs in regular VLBI observations when RFI is present.     

从微波爆发的精细结构谱估算粒子能量及磁场位形

本文采用荷兰Ｄｗｉｎｇｌｏｏ射电天文台的多通道频谱仪（４－８ＧＨｚ）所观测到的一种典型的精细结构事例（ＴｙｐｅＨａｎｄ）来证实源区存在小尺度磁场结构以及电子的短时标加速过程．进一步根据实测和理论分析估算电子的平均速度大约为光速的十分之一，微磁流管直径大约为６００ｋｍ．以及在短时标（０．１ｓ）加速过程中电子能量密度的演化．由此可见，在射电精细结构的动态频谱中含有极其丰富的物理信息，对太阳耀斑机制的理解具有重要意义．     

Spectral characteristics of medium-sized solar radio events

Peak intensities at different frequencies, as reported by several solar radio patrol stations, are used to study the spectrum at the time of maximum intensity of medium-sized solar radio events that cover both the centimetric and metric frequency bands. Two types of spectrum can be distinguished: a V-type of spectrum, where the straight lines, that can be drawn to represent the centimetric and the metric branches, meet each other at a frequency somewhere in the decimetric frequency range and a Jump-type of spectrum, where a discontinuity occurs somewhere in the low-frequency part of the decimetric spectrum. The aspect of the radio response at 600 MHz may have a character which is more centrimetric or more metric. Its character tends to correspond to the spectral branch (metric or centimetric) to which, according to the spectrum, the 600 MHz burst belongs. It is concluded that the centimetric and the metric branch of a cm/m-event are largely independent of each other. It is suggested that a Jump-type of spectrum occurs if some condition relating to the coronal magnetic field is fulfilled.     

A method for arc-second determination of solar burst emission centers with high time resolution and sensitivity at 48 GHz

A 48 GHz five-radiometer front end was installed at the Cassegrain focus of the 13.7-m Itapetinga antenna for the observation of solar bursts. The system works with five beam patterns partly overlapping. The five antenna temperatures are recorded with a temporal resolution of 1 millisecond, including time and antenna position. The ratios of the incoming antenna signals are used to determine the centroid of burst emission. Its coordinates are determined from groups of three receivers by using a least-square fit. In favourable observing conditions we obtain an angular accuracy of about 2 arc sec (r.m.s.), with a time resolution of 1 ms and a sensitivity of 0.05 s.f.u. The accuracy of the antenna tracking, the absolute pointing and the quality of radio seeing at Itapetinga are discussed. A preliminary analysis of an impulsive solar burst event is used to illustrate the capabilities of the method described here.