ATS-6 Radio Beacon Experiment: The First Year

The Radio Beacon Experiment is designed to measure the total electron content and ionospheric content between the satellite and any observer within its field of view. Since Applications Technology Satellite-6 (ATS-6) is visible from about 43 percent of the Earth's surface, an international community of observers have made measurements using it. The radio parameters have to be measured to an accuracy of a few percent, which requires good system calibration and stability. The spaceborne beacon transmits signals on frequencies of 40, 140, and 360 MHz with amplitude modulations of 1 MHz and/or 0.1 MHz for the measurement of modulation phase, Faraday rotation, and amplitude. The overall system objectives and requirements are discussed along with the design of the ATS-6 transmitter and the receiver in Boulder, Colo. The role of the principal investigator in the context of the international program is considered with particular reference to the joint National Oceanic and Atmospheric Administration (NOAA)/Max Planck Institute (MPI) observation program. Monthly median hourly values of total content, plasmaspheric content, and shape factor show distinct diurnal and seasonal variations. A specific event is described to illustrate the use of a spaced receiver network.     

Orbit Determination Accuracies Using Satellite-to-Satellite Tracking

The results are reported of the ATS-6/GEOS-3 and the ATS-6 NIMBUS-6 satellite-to-satellite orbit determination experiments. NASA intends to use the tracking data relay satellite system for operational orbit determination of NASA satellites. Hence, in the near future, satellite-to-satellite tracking data will be routinely processed to obtain orbits. The satellite-to-satellite tracking system used in the ATS-6/NIMBUS-6 and ATS-6/GEOS-3 experiments performed with a resolution of 1 to 2 m in range and less than 1 mm/s in range rate for a 10-s averaging. A Bayesian least squares estimation technique utilizing independent ranging to the synchronous relay satellite was determined to be the most effective procedure for estimating orbits from satellite-to-satellite tracking data. The use of this technique yields estimates of user satellite orbits which are comparable in accuracy to what is usually obtained from ground based systems.     

Substorm-associated injections of energetic ions observed by GEOS-1 and ATS-6 in and near synchronous altitude

Energetic ion measurements of GEOS-1 and ATS-6 are analysed for the period of geomagnetic activity following the arrival of a solar wind shock at 0027 UT on July 29, 1977. GEOS crossed the magnetopause at 6.9 R _E and 0027 UT (1312 LT). Although the difference in local time to ATS at 6.6 R _E is only 2 h ATS seems to remain well inside the magnetopause. During the second orbital pass on this day GEOS crossed the geostationary orbit at the onset time of a major substorm developing at 1120 UT. At this time the local time difference of GEOS and ATS was 12 h. The considerably different energy dispersions are discussed. An azimuthal anisotropy of approximately 20% observed in the GEOS data is interpreted to be the result of a particle density gradient.NOAA-SEL, Boulder, Colo., U.S.A.     

Hectometric and kilometric solar radio emission observed from satellites in August 1972

Type II, III, and continuum solar radio events, as well as intense terrestrial magnetospheric radio emissions, were observed at low frequencies (10 MHz to 30 kHz) by the IMP-6 satellite during the period of high solar activity in August 1972. This review covers briefly the unique direction finding capability of the experiment, as well as a detailed chronology of the low frequency radio events, and, where possible, their association with both groundbased radio observations and solar flares. The attempted observation of solar bursts in the presence of intense magnetospheric noise may, as illustrated, lead to erroneous results in the absence of directional information. The problem of assigning an electron density scale and its influence on determining burst trajectories is reviewed. However, for the disturbed conditions existing during the period in question, we feel that such trajectories cannot be determined accurately by this method. In conclusion, the capabilities, limitations, and observing programs of present and future satellite experiments are briefly discussed.     

Guided propagation of HF radio waves in the ionosphere

A review is given of the work done in the field of ionospheric guided propagation of HF radio signals from artificial satellites. The possible theoretical approaches to the problem are summarized with more details on the analysis in terms of ray-tracing based on a geometric-optics treatment.A survey is done of the experimental observations performed through satellite transmissions, with particular emphasis on the results obtained through three ad hoc developed experiments: Orbis, S. Marco and OV 4.     

Interplanetary type III radio bursts observed from high southern heliographic latitudes

Type III radio bursts observed from high southern latitudes are analyzed for the first time. The continual observation of these radio bursts by Ulysses from after the Jupiter swing-by to 50°S latitude argues for a wide latitudinal directivity of type III radiation. From this high latitude perspective, type III radio sources that lie in the far hemisphere of the Sun with respect to Ulysses are unambiguously resolved for the first time. Using the Ulysses direction-finding capabilities, the radio source locations in the 3-D heliosphere are derived for a radio event on 31 January 1994 when Ulysses was 45°S latitude. The source locations describe a spiral-like trajectory originating from the far side of the Sun. The angular radii of these radio sources are compared to angular radii that were previously derived from in-ecliptic observations.     

弓网电弧辐射特性及对机场下滑信标的影响

为获得弓网电弧辐射特性及从理论上分析其对机场下滑信标的影响。选择典型电气化动车线路,首先基于CISPR16-1标准,利用电磁干扰接收机对电分相和普通点处的弓网电弧电磁辐射进行点频测试,获得了其在下滑信标台频谱内的辐射特性,然后基于电波传播理论,以电气化轨道平行跑道为例,分析了弓网电弧电磁辐射对飞机导航的影响。结果表明：电弧电磁辐射具有一定的随机特性,普通点处产生的电磁辐射场强小于电分相处;普通点的电磁辐射不会对飞机的导航产生干扰;当轨道距跑道中心的距离分别为700、120和60 m时,电分相拉弧点距下滑信标台天线的距离应分别小于3 291、546和249 m时才不会对飞机的导航产生干扰。本结果能够为轨道电气化和民用航空这两大工业体系在机场区域的电磁兼容性设计提供依据。     

Electron precipitations and polar auroras

In the first part (Sections I–III) a brief historical review of the progress of our knowledge of the precipitation of auroral electrons is given. Observations by different techniques, in terms of detectors aboard balloons, sounding rockets, and polar-orbiting satellites, are reviewed (Sections I). The precipitation morphology is examined in terms of synoptic statistical results (Section II) and of latitudinal survey along individual satellite passes (Section III). In the second part (Section IV), a large number of simultaneous observations of auroras and precipitating auroral electrons by DMSP satellites are examined in detail, and it is shown that precipitation characteristics of auroral electrons are distinctly different for the discrete aurora and the diffuse aurora. In the third part (Section V), the source region of auroral electrons is discussed by comparing the auroral electron precipitation at low altitudes observed by DMSP satellites with the simultaneous ATS-6 observations near the magnetospheric equatorial plane approximately along the same geomagnetic field line. It is shown that the diffuse aurora is caused by direct dumping of the plasma sheet electrons from the equatorial region, whereas discrete auroras require acceleration of electrons between the plasma sheet and the polar atmosphere. The parallel electric field along the geomagnetic field line above the ionosphere is a likely candidate for the acceleration mechanism.Applied Physics Laboratory, The Johns Hopkins University, Laurel, Maryland 20810, U.S.A.     

Tracking of DABS-Equipped Aircraft

The Discrete Address Beacon System (DABS) is scheduled to replace the Air Traffic Control Beacon System (ATCRBS) as the prime sensing tool for air traffic control in the 1980's. The design of DABS requires knowledge of the tracking accuracy obtainable as a function of various system parameters. In particular, the potential value of air-to-ground telemetry of turn-rate data and its effect on intermittent positive control (IPC) must be assessed. The design of DABS tracking algorithms is discussed, and the results obtained with a Kalman tracker simulation are given. The major finding is that turn-rate telemetry of moderate accuracy can improve tracking by a factor of 6 to 10.     

Nonthermal radio emission from the Galaxy

Synchrotron radio emission from interstellar space has long been recognized as a useful tool to probe into the galactic distribution of high energy electrons and magnetic fields. We first review the results obtained from the local (<2kpc distant) region of the Galaxy and conclude that the observed local synchrotron emissivity is consistently explained by the measured cosmic ray electron spectrum and the interstellar magnetic field if some reasonable assumptions are allowed. The large scale distribution of radio emissivity shows evidence for spiral structure and is likely to originate in two distinct disk systems: a thin disk (thickness 250 pc in the inner Galaxy) formed by population I objects which emits about 10% of the galactic radio luminosity and a thick disk (2.5 kpc thick in the inner Galaxy) which constitutes the truly diffuse emission and produces 90% of the total luminosity.     

The Effects of Defruiting on the ATCRBS

The defruiter that is employed in the Air Traffic Control Radar Beacon System (ATCRBS) to prefilter asynchronous replies has a complex impact on the detection, estimation and validation properties of the detection subsystem. Its positive and negative effects are quantitatively enumerated via a simulation of the beacon processing subsystem of the Automated Radar Terminal System (ARTS III). It is concluded that the disadvantages of using the present-day defruiter in the ARTS III digital processing channel outweigh the advantages when fruit rates are below several thousand per scan. As an alternative to the total elimination of the defruiter a more general class of preprocessors is defined and their input-output relationships are derived using a Markov Chain formulation. These are found to represent an improvement over the current defruiter in that the positive effects of defruiting are retained while some of the negative effects are reduced.     

ATS-6 Technical Aspects of the Health/Education Telecommunications Experiment

The Health/Education Telecommunications (HET) Experiment involved six different experiments conducted under the auspices of the Department of Health, Education, and Welfare (HEW) with technical assistance from NASA. The HET Experiment on ATS-6 was operated and controlled from a network coordination center in Denver, Colo., which included a 4-and 6-GHz Earth station. The HET Experiment used remote Earth terminals with 3-m-diameter dishes having a 35 dB gain at 2.5 GHz. In addition, comprehensive terminals operating at both C-band and S-band were used for communications with Alaska. The total network involved a complex of satellite and land links at C-band, S-band, and very high frequency (VHF), using the ATS-1, ATS-3, and ATS-6 satellites. The network performance exceeded expectations with remote terminal operations exhibiting a peak-to-peak signal to weighted rms noise ratio of 49 dB at least 99 percent of the time. The remote site operators performed well and were well motivated although they had little previous technical experience.     

ATS-6 Preliminary Results from the 13/18-GHz COMSAT Propagation Experiment

The 13/18-GHz COMSAT Propagation Experiment (CPE) is reviewed, the data acquisition and processing are discussed, and samples of preliminary results are presented. The need for measurements of both hydrometeor-induced attenuation statistics and diversity effectiveness is brought out The facilitation of the experiment-CPE dual frequency and diversity site location, the CPE ground transmit terminals, the CPE transponder on Applications Technology Satellite-6 (ATS-6), and the CPE receive and data acquisition system-is briefly examined. The on-line preprocessing of the received signal is reviewed, followed by a discussion of the off-line processing of this database to remove signal fluctuations not due to hydrometeors. Finally, samples of the results of first-level analysis of the resultant data for the 18-GHz diversity site near Boston, Mass., and for the dual frequency 13/18-GHz site near Detroit, Mich., are presented and discussed.     

Pulsar radio emission

25 years after their discovery, pulsars still pose fundamental problems, in particular when the whole range of their periodsP is considered: 1.56 ms P0.09 s. This communication reviews my understanding of the pulsar magnetosphere, windzone, and (coherent) radio emission. New are details of the preferred magnetic structure, wind generation, and amplification of the emitted (pseudo) curvature radiation, the inferred brightness of which exceeds that of all other terrestrial and astrophysical sources by many orders of magnitude.     

Medium frequency broadcast of differential GPS data

The broadcast performance of DGPS (differential global positioning systems)/radio beacons is studied. It is found that a combination of receiver limiting and forward error corrections is very effective against the atmospheric noise which characterizes the MF band. This combination significantly reduces the probability of bit error and the average time between differential updates. The authors compute the probability of link outage versus range, and find that forward error correction significantly increases DGPS/radio beacon coverage. It is found that groundwave/skywave interference slightly increases the probability of outage at moderate ranges. An estimate is made of the expected duration of outage for the DGPS/radio beacon signal. All results are based on analytical and experimental results     

水下单信标导航航路规划和最优航路接近方法

相比于传统的长基线和超短基线等导航方式，水下单信标导航具有布放简单的优点，但其导航精度有待进一步提高。为此，提出了单信标导航的航路规划方案，通过泰勒级数展开推导了水平位置精度因子的表达式，并分析了导航点和声信标的相对几何位置关系对导航精度的影响，最终提出了航路规划方案。在此基础上，还提出了自主水下航行器(autonomous underwater vehicle，AUV)从其他位置接近最优航路的方法，包括两部分：一是建立以时延为观测量的滤波模型，利用滤波算法实时获取AUV的位置估计值；二是基于可观测度分析结果对最优航路接近过程的轨迹进行了设计。二者的结合使得AUV高效率且高精度地逼近最优航路。仿真证明了采用所提出的航路规划方案和最优航路接近方法可以提高导航精度，航路规划方案使得AUV位置估计的均方根误差近似为2 m。     

Satellite observations of type III solar radio bursts at low frequencies

Type III solar radio bursts have been observed from 10 MHz to 10 kHz by satellite experiments above the terrestrial plasmasphere. Solar radio emission in this frequency range results from excitation of the interplanetary plasma by energetic particles propagating outward along open field lines over distances from 5 R to at least 1 AU from the Sun. This review summarizes the morphology, characteristics and analysis of individual as well as storms of bursts. Substantial evidence is available to show that the radio emission is observed at the second harmonic instead of the fundamental of the plasma frequency. This brings the density scale derived by radio observations into better agreement with direct solar wind density measurements at 1 AU and relaxes the requirement for type III propagation along large density-enhanced regions. This density scale with the measured direction of arrival of the radio burst allows the trajectory of the exciter path to be determined from 10 R to 1 AU. Thus, for example, the dynamics and gross structure of the interplanetary magnetic field can be investigated by this method. Burst rise times are interpreted in terms of exciter length and dispersion while decay times refer to the radiation damping process. The combination of radio observations at the lower frequencies and in-situ measurements on non-relativistic electrons at 1 AU provide data on the energy range and efficiency of the wave-particle interactions responsible for the radio emission.     

Planetary radio astronomy experiment for Voyager missions

The planetary radio astronomy experiment will measure radio spectra of planetary emissions in the range 1.2 kHz to 40.5 MHz. These emissions result from wave-particle-plasma interactions in the magnetospheres and ionospheres of the planets. At Jupiter, they are strongly modulated by the Galilean satellite Io.As the spacecraft leave the Earth's vicinity, we will observe terrestrial kilometric radiation, and for the first time, determine its polarization (RH and LH power separately). At the giant planets, the source of radio emission at low frequencies is not understood, but will be defined through comparison of the radio emission data with other particles and fields experiments aboard Voyager, as well as with optical data. Since, for Jupiter, as for the Earth, the radio data quite probably relate to particle precipitation, and to magnetic field strength and orientation in the polar ionosphere, we hope to be able to elucidate some characteristics of Jupiter auroras.Together with the plasma wave experiment, and possibly several optical experiments, our data can demonstrate the existence of lightning on the giant planets and on the satellite Titan, should it exist. Finally, the Voyager missions occur near maximum of the sunspot cycle. Solar outburst types can be identified through the radio measurements; when the spacecraft are on the opposite side of the Sun from the Earth we can identify solar flare-related events otherwise invisible on the Earth.