Improvements in target ranging by HF radar using the European ionospheric model PRIME

Target ranging by HF radar can be done by correcting the group path of target echoes for the delay due to the propagation through the ionosphere. One possibility is to simulate the propagation by ray-tracing but in this case the final accuracy obtained in target registration depends mainly on the quality of the ionospheric model used to raytrace. In this study, the PRIME ionospheric model has been used to perform ray-tracing on a 950 km path, between Toulon and Lannion, for which oblique soundings data from the SCIPION sounder are available for December 1991. The ray-tracings were performed by using the vertical electron density profiles at five points along the path calculated by PRIME for monthly median and/or instantaneous conditions. Vertical electron density profiles from the IRI model have also been considered for comparison. The results of this investigation are presented and the accuracy in target ranging is discussed as obtained for the conditions of the simulations.     

The Study on the Group Delay Jumping of CE-4 VLBI System

The phase delay software is a key component of VLBI (Very Long Baseline Interferometry) orbit determination system in CE-4 mission, which is critical to deep space exploration. When processing X-band DOR (Differential One-way Ranging) signals of probes in the past, the group delay jumping occasionally occurred in the observed scan. This paper consists of two parts. First, according to the VLBI station signal reception and VLBI center data processing steps, we analyzed the frequency, phase, power, and self-correlation spectrum of the signal, and located the influencing factor at the abnormal analog signal of Kunming (KM) station. Second, the group delay jumping was revised by the post-correction method, which was based on the analysis of the abnormal unwrap phase. We used the corrected phase to get the new group delay, and used orbit determination software to verify the effectiveness of the post-correction method, which upgraded the phase delay processing software.     

嫦娥四号VLBI群时延跳变研究

相时延处理软件是嫦娥四号(CE-4)任务甚长基线干涉测量(Very Long Baseline Interferometry,VLBI)测轨分系统软件配置项之一,利用其处理着陆巡视器X波段DOR(Differential One-way Ranging)信号时,观测弧段(scan)内偶尔存在残余群时延跳变问题.论文主要分为两部分:一是根据VLBI信号接收和数据处理流程,从相关相位、频率、幅度和功率方面进行分析,最终将影响因素定位在昆明测站模拟信号异常;二是以scan内时延跳变影响因素分析为基础,通过修正异常基线相关相位,研究残余群时延跳变事后改正方法,并利用定轨软件验证其有效性,升级了相时延处理软件.     

Radio Wave Propagation in the Corona and the Interplanetary Medium

Radio wave propagation through an inhomogeneous, random plasma produces a variety of observable phenomena – group delay, Faraday rotation, refraction, angular broadening, spectral broadening, and scintillations in phase, amplitude, and frequency. These may be exploited to constrain the mean and fluctuating properties of the medium through a variety of remote sensing techniques. In the case of the solar corona and the solar wind, the mean density, magnetic field, solar wind speed, and the spatial spectrum of the density fluctuation scan all be constrained in regions that are inaccessible to in situmeasurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Theory of decametric radio emissions from Jupiter

It is suggested that the Jovian decametric emissions (DAM) originate in a cyclotron instability of weakly relativistic electrons trapped in the Jovian magnetic field. The resulting radiation has a group velocity in the magnetosphheric plasma which may be of order 10²km/sec, and thus takes much more time to escape the magnetosphere than if the group velocity were at or near the speed of light. Therefore, the asymmetry of the Io phase with respect to sources east and west of the Earth-Jupiter line does not imply an asymmetric beaming of DAM; it is caused by the delay the waves experience in traversing the magnetosphere. The frequency drifts of milli- and decasecond bursts are also explained. It is found that the rotation of the magnetosphere can play an important role, since the observer views the propagation velocity of the waves as the sum of their group velocity and the velocity of the medium itself. The rotation velocity is in opposite directions, relative to the observer, for sources east and west of the Earth-Jupiter line; the resultant vector addition gives positive frequency drifts for decasecond bursts from the early and fourth sources, and negative drifts for bursts from the main and third sources. The negative drifts of millisecond bursts may be the result of large density gradients of plasma in a temporarily compressed magnetosphere.     

Possible use of the LOCAPI ionospheric prediction software to digital communications

The LOCAPI ionospheric propagation software, developed by the University of Rennes 1, uses the multiquasi-parabolic expression for the electron density profile. Its inputs are : date, frequency, transmitting and receiving locations. An original fast and accurate algorithm determines the output parameters : MUF, occultation LUF, elevation angles, group delays, pathlosses for an important range of possible O and X propagation modes. The accuracy of the simulated results permits the use of LOCAPI software to determine the slope of the group time delay as a function of frequency of HF radio links, for each propagation mode, and to evaluate the coherent bandwidth for a digital communication channel. In addition, improved results can be obtained if the polarization and antennas effects are taken into account.     

Method of locating the Pc 1 source and hot plasma parameters in the generation region

A method of estimating hot and cold plasma parameters using ground Pc 1 observations is proposed. The values of both hot and cold plasma concentrations, proton energy and temperature anisotropy in the Pc 1 generation region are calculated. It is shown that the most appropriate (effective) indicator of the L-shell, where Pc 1 are generated, is the group delay of wave packets.     

On the effects of the interaction of relativistic jets with interstellar gas

We investigated the observed effects of the interaction of a fast-growing spiral bunch of quantum, jet-composing vortices with interstellar gas of varying density. The problem was studied within the framework of the earlier-developed quantum-vortex model of relativistic jets in quasars, radiogalaxies, and active galactic nuclei. The formula describing the gas density effect on the jet growth delay was derived.     

The secular modulation of solar rotation from 1943 to 1992 and its time-delayed correlation with the 55-year grand cycle of the 11-year solar cycle

We devised a new method, which we call the running-segment method, to achieve high-resolution time series of indices of solar rotation for determining the latitude dependence of the differential rotation by a least-squares fitting of the daily translation of positions of sunspot groups during a fixed time segment of 11 years. The segment is moved by an amount of one year to determine the differential profile of the next point of time. Time of the determined rotation data is defined by an arithmetic mean of the beginning and ending years of the segment. The rotation underwent an acceleration from 1948 to 1974 and a deceleration from 1974 to 1987. We found that the time profile of the indexM, the angular momentum surface layer density defined by integration of the angular momentum volume density over the whole surface, follows almost exactly the time profile of the 11-year running mean of the yearly mean of the sunspot relative number with a delay time of about 20 years. The acceleration (deceleration) phase corresponds to the ascending (descending) phase of amplitude of the 11-year solar cycle of cycle 16 (19) to cycle 19 (20) with a delay time of about 20 years. The cycles 15–20 correspond to the 55-year grand cycle V of the 11-year cycle. The delay time of about 20 years agrees well with the delay time predicted by a nonlinear dynamo theory of the solar cycle for driving the 55-year modulation of the 11-year solar cycle. The agreement suggests that the Lorentz force of the magnetic field of the solar cycle during grand cycle V drives the solar rotation modulation from 1948 to 1987 and that the force needed about 20 years to modify the rotation during 1943–1992.     

TheHI content of the Eridanus group of galaxies

The HI content of galaxies in the Eridanus group is studied using the GMRT observations and the HIPASS data. A significant HI deficiency up to a factor of 2–3 is observed in galaxies in the high galaxy density regions. The HI deficiency in galaxies is observed to be directly correlated to the local projected galaxy density, and inversely correlated to the line-of-sight radial velocity. Furthermore, galaxies with larger optical diameters are predominantly in the lower galaxy density regions. It is suggested that the HI deficiency in Eridanus is due to tidal interactions. In some galaxies, evidences of tidal interactions are seen. An important implication is that significant evolution of galaxies can take place in the group environment. In the hierarchical way of formation of clusters via mergers of groups, a fraction of the observed HI deficiency in clusters could have originated in groups. The co-existence of S0s and severely HI deficient galaxies in the Eridanus group suggests that tidal interaction is likely to be an effective mechanism for transforming spirals to S0s.     

The influence of the surroundings on the morphology of galaxies

The characteristics of galaxies within galaxy groups are investigated as a function of the surroundings. It is shown that the relative number of the galaxies with different morphological type is correlated with the number of members within the group, but the fraction of E+S0 galaxies does not depend on the mean-pairwise distance between the galaxies, the density of the luminous matter as well as the velocity dispersion in the group.     

Thermal history of inter-cluster relativistic electron gas heated by quasars

The thermal evolution of an inter-cluster gas of relativistic electrons heated by quasars with redshifts up toz=3 and 4 is studied in the framework of a Friedmann-Robertson-Walker universe. The gas cools by Compton scattering with the microwave backgroud radiation and by adiabatic cooling due to the universe expansion. Power and exponential laws of cosmological evolution of the comoving density of sources are considered. The obtained temperatures are sensitive to the form of these laws and to the heating epochs. Compared to the nonrelativistic models, the results obtained in the case of the power law present strong differences. These differences decrease when the exponential law is considered. Thermalization times are compared to the characteristic time of variation of the universe energy density and to the time-scales of energy loss by bremsstrahlung radiation and by Compton scattering. It is shown that, in some cases, nonequilibrium effects may be important. The time delay effects in the propagation of electromagnetic waves in cosmic plasma are shown to be very important for the analysis of theoretical models.     

Variable radio echoes from a jet in QSO 0957+561

Time delay determinations in astrophysics are used most often to find time delays between flux density variations of different spectral bands and/or spectral lines in AGNs and different images of gravitationally lensed QSOs. Here we consider a new algorithm for a complex case, when the time delay is itself a linear function of time and the intensity of echo response is power function of the delay. We apply this method to investigate optical-to-radio delay in the double quasar 0957+561, which is a generally accepted case of gravitational lensing.Radio-optical correlation in QSO 0957+561 was first reported by Oknyanskij and Beskin (1993, hereafter OB) on the basis of radio observations made in the years 1979 to 1990. OB used an idea to take into account the known gravitational lensing time delay to get combined radio and optical light curves and then to use them for determination of the possible radio-from-optical time delay. It was found this way that radio variations (5 MHz) followed optical ones by about 6.4 years with high level of correlation (0.87). Using new radio data (Haarsmaet al., 1996), for the interval 1979–1994 we find nearly the same value for the optical-to-radio delay as has been found before. Additionally we suspect that the time delay value is linearly increasing at about 110 days per year while the portion of reradiated flux in the radioresponse is decreasing.Obtained results indicate that the optical and radio emitting regions are physically related, but have distinct size scales, locations and possibly radiation mechanisms. We conclude that the results can be explained by simple model were the variable radio source is ejected from the central part of the QSO compact component and that the changing time delay between the optical and radio light curves is consequence of light travel effect.     

一例奇特长延迟硬X射线耀斑的解释

1989年3月6日1354－1624UT的3B级大耀斑硬X射线的峰值延迟长达130秒，而硬X射线的最低能道上升至峰值的时间（上升沿）却只有150秒。在利用电子的捕获沉降模型来解释这一奇特事件，发现当日冕密度取10^9cm^-3且存在双源作用时，捕获沉降模型可以解释观测结果。     

When is star formation episodic? A delay differential equation 'negative feedback' model

We introduce a differential equation for star formation in galaxies that incorporates negative feedback with a delay. When the feedback is instantaneous, solutions approach a self-limiting equilibrium state. When there is a delay, even though the feedback is negative, the solutions can exhibit cyclic and episodic solutions. We find that periodic or episodic star formation only occurs when two conditions are satisfied. First the delay time-scale must exceed a cloud consumption time-scale. Secondly, the feedback must be strong. This statement is quantitatively equivalent to requiring that the time-scale to approach equilibrium be greater than approximately twice the cloud consumption time-scale. The period of oscillations predicted is approximately four times the delay time-scale. The amplitude of the oscillations increases with both feedback strength and delay time.
We discuss applications of the delay differential equation (DDE) model to star formation in galaxies using the cloud density as a variable. The DDE model is most applicable to systems that recycle gas and only slowly remove gas from the system. We propose likely delay mechanisms based on the requirement that the delay time is related to the observationally estimated time between episodic events. The proposed delay time-scale accounting for episodic star formation in galaxy centres on periods similar to   P ∼ 10 Myr  , irregular galaxies with   P ∼ 100 Myr  , and the Milky Way disc with   P ∼ 2  Gyr, could be that for exciting turbulence following creation of massive stars, that for gas pushed into the halo to return and interact with the disc and that for spiral density wave evolution, respectively.     

致密射电源短时标变化的相对论效应

本文讨论相对论激波在喷流中传播时,由照明不均匀性所引起的同步加速辐射问题中的某些相对论效应.研究激波的结构和厚度以及不均匀性尺度对于辐射变化的时标和变幅的关系.结果表明,由于激波辐射区的厚度对于光学辐射和射电辐射的不同,可能引起射电变化相对于光学变化的时间迟延,从而对某些观测现象提供了一种解释.     

应用矢量网络分析仪测定变频器的群时延特性

群时延是系统和网络的一项重要传输特性,它表征系统和网络的线性失真。讨论了采用高性能PNA系列矢量网络分析仪测量变频器群时延的方法,并结合实例对实现测试的关键点和技巧进行了阐述,最后给出测试结果及不确定度的分析。     

Fundamental and Harmonic Emission in Type III Solar Radio Bursts – I. Emission at a Single Location or Frequency

A model of type III solar radio bursts is developed that incorporates large-angle scattering and reabsorption of fundamental emission amid ambient density fluctuations in the corona and solar wind. Comparison with observations shows that this model accounts semiquantitatively for anomalous harmonic ratios, the exponential decay constant of bursts, burst rise times, and the directivity of fundamental emission. It is concluded that the long emission tail on interplanetary type III bursts is mostly fundamental emission, while much of the anomalous time delay of fundamental relative to harmonic emission from a given location must be ascribed to other causes.     

Variations in air density at heights near 150 km, from the orbit of the satellite 1966-101G

The satellite 1966-101G was launched on 2 November 1966 into an orbit with an initial perigee height of 140 km. A satellite with such a low perigee usually decays within a few days, but 1966-101G was exceptionally dense and remained in orbit until 6 May 1967. Analysis of the changes in its orbital period provides an unique opportunity for studying continuously for six months the variations in air density at a height near 150 km.

This paper records the results of such an analysis, applicable for the (medium) level of solar activity prevailing early in 1967. It is shown that at a height of 155 km the air density is greater by day than by night, with the maximum daytime density exceeding the minimum night-time density by a factor of 1.7: in contrast the COSPAR International Reference Atmosphere 1965 predicts that the density should be slightly greater by night than by day. It is also found that the night-time density increases as solar activity increases, and that the density scale height given by CIRA 1965 at heights near 150 km is too low, perhaps by about 20%.     

A Possible Means of Improving the Accuracy of Refraction Delay Correction of Neutral Atmosphere

The space geodetic technology requires an accurate model of correction of refraction delay by the neutral atmosphere that varies from one observing station to another, and from one azimuth to the next. It is pointed out that under the present condition the astronomical refraction can not yet be directly determined, any correction model because of its high dependence on the assumed atmospheric distribution, is incapable of achieving the required accuracy or of improving the cut-off altitude. In this paper, based on the special properties of the lower latitude meridian circle at Yunnan Observatory and our experience of determining atmospheric refraction therewith, a new method is proposed for improving the accuracy of refraction delay correction. Namely, the measured data of astronomical refraction of an observing station from near zenith to low altitudes in different azimuths are used to evaluate the refractivities and the parameters of the mapping functions, thereby establishing a model of atmospheric refraction delay correction that varies with the observing station and the azimuth. Since it is unnecessary for the new method to adopt any atmospheric distribution model, application of this new method will improve correction accuracy of refraction delay to better than 1mm at zenith and to centimeters at low altitudes, and improve the cut-off altitude to below 5 degrees.