Edited by Masashi Hayakawa

E1. Natural Radio Noise Sources

E1.1. Lightning

Studies concerning the summer and winter lightning have been ongoing.

Observation of electric and magnetic field waveforms associated with lightning discharges was carried out in Indonesia, and its comparison with Japanese lightning suggests that the waveform parameters of return strokes in summer are nearly the same in both countries (Ishii et al., 1990a). Ishii and Hojo (1991) have observed the cloud-to-ground lightning discharges in Niigata area to find their seasonal variation and the occurrence probability of high return stroke current. Characteristics of winter thunderstorms have been investigated by Kitagawa (1992) and Goto and Narita (1991a,b). Kitagawa (1992) has studied the mechanism of charge separation in winter thunderclouds in which the separation takes place most effectively around the temperature level of -10C. Goto and Narita (1991b) have studied the meteorological conditions for the occurrence of winter thunderstorms. Based on the study of em pulses of lightning return strokes Yamamoto et al.(1991) have found anomalous features of return strokes of winter thunderstorms. Characteristics of lightning flashes with multiple strikes to the ground within one second are studied (Takagi et al., 1991b). Miyazaki et al.(1991b) have proposed a lightning strength parameter. The Fourier spectra of the electric and magnetic fields of lightning discharges have been estimated by Kawasaki et al.(1991c), and VHF/UHF radiation characteristics in lightning return stroke processes are reviewed by Nakano (1992) and Nakano et al.(1991b).

The observation of winter lightning strikes to an isolated tower has been continued using magnetic links, digital recording system, field mills, still camera and video camera systems, and it is found that winter lightning strokes often have a very long duration or continuing current and sometimes have a very large amplitude over 200 kA in positive flashes (Goto et al., 1990, 1991). Rocket-triggered lightning experiments have been continued. The electric and magnetic field changes and UHF radiation are observed during the rocket-triggering experiments in winter and a remarkable discrepancy is noticed between electromagnetic field changes of flashes triggered with a rocket and isolated wire that struck a power tower and flashes with a rocket and a ground wire (Kawasaki et al., 1991a; Kanao et al., 1991). Nakano et al.(1991a) have measured the electromagnetic fields at the distance of 3.6 km from lightning and compared them with those of lightning current waveforms. Nakamura and Horii(1991) have summarized the experiments of artificially triggered lightning in Japan based on eighty four strikes since 1977, and Kawasaki and Mazur (1992) have studied the common physical processes in natural and triggered lightning in winter storms in Japan.

A theoretical model for the calculation of lightning return stroke electric fields above a finite conductive earth is presented by Kawasaki et al.(1990). A stepped leader near the ground surface has been numerically simulated by means of the leader progression model based on the fractal concept (Kawasaki et al., 1989). Takagi et al.(1991a) have represented the leader and return stroke channels in terms of coaxial cylindrical electrodes with a short circuit, and their measured corona sheath currents are compared with those calculations.

Simultaneous observation of lightning current to a tower, induced voltages on a test distribution line and vertical electric field waveforms have been carried out by Ishii et al.(1990b). The simultaneous measurement of vertical and horizontal electric fields associated with return strokes has been done and it is found that the horizontal electric field is related to the vertical electric field by the wavetilt formula (Michishita et a., 1990a,b, 1992).

E1.2. Atmospheric Radio Noise

A comprehensive review is given on the Earth's electric fields, covering the atmospheric electric field, atmospherics, the ionospheric and magnetospheric electric fields, the auroral electric field, and the electric field in the Earth's crust in the frequency range from DC to VLF (Ogawa, 1989). Fraser-Smith et al.(1991) have studied the characteristics of radio noises observed at Kochi, and reported that the noise statistics tend to be more typical of lightning-generated ELF/VLF noise than those of higher latitude stations where magnetospheric noises are predominant. The waveforms of tweek atmospherics are analyzed theoretically by the theory of mode currents (Yano et al., 1989b,1991a). Baba et al.(1991) have elucidated the wave characteristics of tweek atmospherics (incident and azimuthal angles, and the wave polarization and their frequency depencdences) by using the field analysis direction finding, and Baba et al. (1993) have tried to interpret these experimental results in terms of the modal equations for realistic ionospheric density profiles.

Sukhorukov et al.(1992b) have made the analytical studies on the propagation in the Earth-ionosphere waveguide for the realistic inhomogeneous and anisotropic ionosphere models, and also Baba and Hayakawa(1993) have utilized the finite element method to solve the influence of localized ionospheric perturbations caused by Trimpi effects on the subionospheric propagation characteristics.

VLF data from the low-altitude Ariel 4 satellite are used to investigate the characteristics of low- and equatorial-latitude VLF radio noises, and it is found that those are originated in lightning discharges (Hayakawa, 1989). Very unusual low-latitude whistlers with the additional traces of the Earth-ionosphere waveguide propagation have been observed by Shimakura et al.(1991a), and their theoretical interpretation is provided by Sukhorukov et al.(1992a). The fading effects observed in whistler spectra are explained in terms of a few wave interference mechanisms (Hagino et al., 1991; Yano et al., 1989a,1991b). Spaced direction finding measurements of very low latitude whistlers are carried out in South China, and it is found that they are attributed to field-aligned propagation (Hayakawa et al., 1991b; Ohta et al.,1990). This field-aligned propagation has been furthermore supported by ray-tracing studies (Ohta et a., 1992). Ohta et al.(1989,1991) have investigated the frequency dependence of arrival direction and wave polarization of low latitude whistlers, which supports their ducted propagation. Shimakura et al. (1991) have studied the formation of whistler ducts based on the analyses of periodicities in whistler occurrence rate. The correlation of occurrence rate of whistlers at Yamaoka with thunderstorm activity near its conjugate region and also with solar activity, has yielded that the ionospheric absorption is of major importance in the long-term variation of whistler occurrence rate, with the duct formation being of secondary effect, while the lightning activity is only a necessary condition (Ohta and Hayakawa, 1990). Hayakawa (1991a) has found from the study of whistler-triggered VLF-emissions observed at Moshiri that triggered emissions take place in two L preferable regions: L=2.1 to 3.4 (electron slot region ) and L=1.6 (inner radiation belt). Whistler diagnostics of magnetospheric parameters have been reviewed by Sazhin et al.(1992).

E1.3. Natural Radio Noises in Space

Direction finding results on board spacecrafts for different magnetospheric VLF/ELF emissions are reviewed and their generation mechanisms are discussed (Hayakawa et al., 1991b). The system of a systematic direction finding for ionospheric ELF waves on board the Aureol-3 satellite has been described, and some results on plasmaspheric ELF hiss has been presented (Hayakawa et al., 1990). Ondoh (1991c) has studied the mid-latitude VLF hiss based on the ISIS VLF satellite data, and has indicated that it is generated in vicinity of the plasmapause by the electron cyclotron instability by energetic electrons. The detailed ray-tracing study of the effect of plasmapause on the VLF/ELF wave propagation has been investigated by Hattori et al.(1991d) and a ray focussing is studied by Ishikawa et al.(1990) in order to indicate its importance in the wave-particle interactions. The statistical properties of VLF/ELF hiss are studied, which indicates that it is considered as a Gaussian stationary random signal, but it includes some kinds of structures such as coherent components (Tsuji et al., 1989). Hayakawa and Sazhin (1992) have published a comprehensive review on mid-latitude and plasmaspheric hiss.

The off-equatorial direction finding is carried out for spontaneous chorus emissions observed by GEOS 1 satellite, and it is found that chorus (rising-tone) is generated near the equator with small q angles (Hayakawa et al., 1991a; Hattori et al., 1990; Hattori and Hayakawa, 1992). Some chorus emissions are found to be triggered by the hiss considered to be incoherent. Hattori et al.(1991a,b) have found based on the detailed spectral analysis and direction finding on GEOS 1 that a wavelet (coherent wave component )near the upper edge of the hiss band is responsible for triggering a chorus. Further studies have indicated an evidence on the threshold of the intensity of hiss wavelet in triggering chorus (Hattori et al., 1991c). A comprehensive review on chorus is published by Sazhin and Hayakawa (1992).

Ondoh (1990a,b, 1991a,b) has obtained the distribution of broadband auroral hiss in the form of MLT and LAT by using the ISIS observations, and suggested that it is generated by Cerenkov radiation by inverted-V electrons. The electrostatic ion cyclotron emissions have been investigated on the basis of the data observed by ISIS, Kyokko and Akebono satellites, and also their relation to auroral emission is studied (Yoshino, 1991a). Electrostatic impulsive plasma waves (1-9 kHz) are also found in DE-1 wideband electric field data, which are discussed in terms of Landau resonant trapping of magnetospheric electrons by the associated whistler-mode ELF hiss (Ondoh, et al., 1990, 1991).

Hayakawa et al.(1992a) have carried out the extensive study of the polarization of magnetospheric Pc1 pulsations at high latitudes and have discussed the generation mechanism of IPDP pulsations. Further statistical characteristics of the polarization of different kinds of Pc1 pulsations are studied(Hayakawa et al., 1992b).

E1.4. Radio Noise Associated with Earthquakes and Volcanic Eruptions

The observational results of electromagnetic emissions at 82 kHz have been presented as precursors to the volcanic eruptions of Mt.Mihara on November 15 and 21, 1986 (Yoshino and Tomizawa, 1990). During the same volcanic eruptions, Ondoh (1990c) has observed the nighttime intensity enhancements of the atmospheric noise at 160 kHz and 80 kHz, which are interpreted as being due to lightning discharges in eruption smokes. The seismogenic radio emissions at 82 kHz, 1.525 kHz and 36 Hz associated with earthquakes and volcanic eruptions have been reviewed on the basis of the data by using the multistation network, and some generation mechanisms have been suggeste (Yoshino, 1991b). The results of statistical analyses of the seismogenic emission data for 52 earth-quake events in the last decade are presented, together with the numerical estimation of attenuation for the surface mode wave propagation along the boundary surface of the fault (Yoshino et al., 1992). A new system of the direction finding method for precursory emissions associated with earthquakes is proposed, which is based on the simultaneous measurement of the waveforms of multiple electric and magnetic field components at ELF (1.5kHz +- 5Hz) and ULF (0-5Hz)(Hayakawa et al., 1993b). Molchanov et al. (1993) have observed the seismogenic emissions in the frequency range of 8 Hz-20 KHz on the Intercosmos 24 satellite during the period of November 16, 1989 to December 31, 1989, and their generation mechanisms have been indicated. It is shown by the laboratory experiment that the electric field is emitted rather than the magnetic field from rock and wood, while the magnetic field is emitted easily from irons (Ogawa et al., 1991). A possible influence of seismic activity on the low-latitude whistlers is noticed, and it is suggested that whistler with large dispersion may be used as a precursor of earthquakes (Hayakawa et al., 1993a).

E1.5. Instrumentation for Natural Radio Noises

A new transient memory is designed to study the whole process of the lightning discharges, which has 1 Mbytes buffer memories and which can record the electric field changes due to lightning discharges for the time period up to 524 ms (Kawasaki et al., 1991d). Kawamata et al.(1990) have presented an error evaluation in measuring the lightning current by the use of a magnetic link and a current shunt or a passive integrator. Then, Kawamata et al. (1991a,b) have presented a magnetic field shielding practice against the heavy lightning electromagnetics. A pair of doughnut shaped static antennas for measuring the electrostatic component of lightning discharges is proposed by Miyazaki et al.(1991a). Automatically driven video camera systems have been developed for the observation of winter lightning (Goto and Narita, 1989).

Kawasaki et al.(1991b) have presented a localization method for the partial discharge by means of the measurement of time difference of arrival. Ohta and Hayakawa (1992) have described an automatic whistler direction finder based on the field-analysis principle. A wave distribution function method is proposed to estimate the wave energy distribution of magnetospheric VLF waves by means of the three field components observed on the ground (Shimakura and Hayakawa, 1991; Shimakura et al., 1992b), and it is applied to the actual whistlers (Shimakura et al., 1992a). The effect of polarization model in the integration kernels in the reconstruction of wave distribution functions is studied by Shimakura and Hayakawa (1992).

Long-gap discharge induction experiments are carried out by using a TEA CO2 laser to investigate the feasibility of laser-induced lightning (Kawasaki et al., 1992).

E2. Man-made Noise

E2.1. Noise Sources

The automobile radio noise has been measured in a frequency band (1-3GHz), and the variation of the impulse height, received in typical traveling conditions, can be expressed as a log-normal distribution and the impulsive emission is Poisson distributed in time (Yamanaka and Sugiura,1990a).

Recent new findings on the relation between arc and erosion in switching contact are summarized with special attention to the role of electrode temperature (Sone et al.,1991). Breaking arc durations and differences between the mass of a contact before and after an experiment are measured in Ag-Pd alloy contacts (Ishida et al.,1990). Microscopical sliding of electric contact due to the spring thermal deformation is measured by a holographic measurement and the relationship between the contact voltage and the deformation of the contact spring due to current flow is made clear (Taniguchi et al.,1990). Sato et al. (1990) have developed an equipment to measure the optical spectrum of contact arcs in real time, and it enables us to study effectively the generation mechanism of electromagnetic noise due to arcs. The frequency spectra of the arc current due to opening electric contacts in air are measured, and it is found that the frequency spectra of the arc current depends on the length and terminal conditions of the line connected with the contacts (Minegishi et al.,1989).

Masugi et al.(1992) have presented the measurement and analytical results of electromagnetic pulses caused by indirect electrostatic discharges, and it is found that the pulses produced by low discharge voltages may introduce strong electromagnetic interferences.

E2.2. Radiation from and Coupling to Lines

The mechanism for radiation phenomenon caused by a finite-length transmission line is reviewed by Kami (1992), who has studied the coupling of an external wave to transmission lines by means of a circuit theory and has applied to the radiation problem. Kami and Sato (1990) have studied the reciprocal relationship between the coupling and radiation for a pair wire line above a conducting ground. Induction of voltages on a signal line of a printed circuit board exposed to an electromagnetic field is investigated by using the microstrip line model and loop model (Yamanaka et al.,1991b). Digital signal fluctuation resulting from voltage or current sources is studied in order to analyze the malfunction of digital IC exposed to electromagnetic fields (Nishikata et al.,1991). Electromagnetic line and field properties, eigen modes, pulse waves, noise characteristics and spectrum spread methods are discussed, and coupling and radiation properties in curvature parts of circuits are also discussed (Miyazaki, 1989).

E2.3. Measuring System and Location of Noise Sources

A new method is proposed to measure the effective radiated power of transmitters, in which the effects of nearby reflecting objects introducing measurement error, are cancelled by the in-phase synthetic method (Yamanaka and Sugiura,1990b). Electric field distribution is measured in the vicinity of a mobile tranceiver and a walkie-talkie, and is compared with the theoretical calculation taking into account the direct wave and the reflected wave from the ground (Yamanaka et al. 1991).

The algorithm of estimating the position and intensity of reflection sources is proposed by Wang et al.(1990), who have applied this algorithm for the analysis of the reflected waves in an ordinary room based on an EM field pattern by a robotic system.

Kawamata et al. (1989) have proposed an observation system by distributed circuit for fast transients due to the discharge in electric contacts. A measurement method for broad-band and long-duration random signals is described using a spectrum analyzer as a receiver, and the amplitude probability distribution and average crossing rate of urban noises and automotive ignition noises are measured by this system (Ohnuma et al.,1990).

E2.4. Electromagnetic Shielding and Absorbers

Tapered multi-layer models are used for accomplishment of broad band and thin radio absorbers and electromagnetic shields (Miyazaki and Tanoue, 1989). Plastic absorption plates are fabricated, for which the characteristics of wave reflection and transmission are investigated in a frequency range from HF to UHF (Miyazaki and Tanoue, 1990).

E2.5. Electromagnetic Wave Scattering

The scattering characteristics of several basic objects with respect to EM-wave propagation in radio communications have been discussed by Miyazaki and Asano (1991). Miyazaki and Asano (1992) have discussed the electromagnetic scattering characteristics for EMC problems in mobile communication and broadcasting systems in terms of the numerical methods, which are useful for applying to complex shaped objects.

E3. Composite Noise

A random pulse stream generator, together with the composite noise generator makes it possible to generate the Middleton's "Class A" noise (Suzuki et al.,1992). By using this system, any kinds of noises, non-Gaussian and also Gaussian, are simulated and this system is used to test an immunity of information equipments or systems (Takagi, 1991). Electromagnetic environment is measured in the Tokyo metropolis by using the spectrum analyzer (Kitani et al.,1992). A measuring system based on the spectrum analyzer controlled by a personal computer, is used to estimate the electromagnetic environment (Echigo et al.,1992).

E4. Effect of Noise on System Performance

E4.1. Effect of Noise on Communication

Subjective TV image evaluation has been carried out by using the composite noise generator, which indicates that the noise power among the different noise parameters, is the most influential (Tanaka et al.,1991). Tanaka and Takagi (1992) have studied the effects of both continuous Gaussian noise and burst Gaussian noise on TV picuture degradation on the basis of subjective evaluation of the disturbances. An estimation method of non-continuous noise characteristics that are converted into TV picture degradation equivalent, is proposed by Ohnuma and Sato (1992).

A new distributed signal transmission system is proposed by Kang et al. (1992), which has an immunity against the noisy channel, and this transimission line has an ability to suppress an impulsive interference.

E4.2. Effect of Noise on Equipment

Minegishi et al. (1992) have studied the effect of transients of an arc discharge initiation due to interrupting current on the distribution constant system consisted of a coaxial switch and coaxial cables, and it is shown that the current drops stepwise at the moment of an interruption current.

E5. Spectrum Management and Utilization

For the practical use of the allotment plan, especially when accommodating modifications or new requirements,it is necessary to establish a workable algorithm to effectively preserve the margins for the unforeseen use, and Ito and Yamada (1991) have proposed a concept of c/e ratio useful in finding the locations of additional requirements. A new interference cancellation technique named In-Band Power Minimizing Method is proposed, which is found to be effective for small earth stations (Minamisono and Satoh, 1992).

A system is proposed to observe the spectum usage and spectrum pollution, which is a spectrum snalyzer controlled by a personal computer. By modifying the display method of the measured data, the spectrum usage and pollution can be recognized at a glance (Echigo et al.,1992).

E6. Biological Effects of Radio Noise

An interactive inversion procedure is presented for noninvasive measurements of the complex permittivity and SAR distributions of two-dimensional bodies, and it is tested numerically by means of a two-layered circular model (Wang and Takagi, 1990). Biological effects on human body inside MRI systems are described by using the two-dimensional boundary element method, and eddy current, field intensities and power deposition are calculated under the RF fields at 42.6MHz and static field strength of 1T (Hanai et al. 1989).


Commission D ('93)

Commission F ('93)

Commission E ('96)

Commission E ('99)


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Hattori, K., M. Hayakawa, D. Lagoutte, M. Parrot, and F. Lefeuvre, An Experimental Study of the Role of Hiss in the Generation of Chorus in the Outer Magnetosphere, as Based on Spectral Analysis and Direction Finding Measurements onboard GEOS1, Proc. NIPR Symp. on Upper Atmosphere Phys., 4, 20-41 (1991b).

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Hayakawa, M., Direction Finding of Magnetospheric VLF/ELF Emissions and Their Generation Mechanism, in "Environmental and Space Electromagnetics", Ed. H. Kikuchi, Springer-Verlag, 155-167 (1991b).

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Kawasaki, Z., J. M. Li, K. Matsuura, M. Kawasaki, and O. Sugimoto, Localization of Partical Dischages Using Time Difference of Arrival of Radiation Fields, Proc. the 3rd Int'l Conf. on Properties and Application of Dielectric Materials, Tokyo, 910-914 (1991b).

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