Tomohiro Oguchi

Measurements of Dielectric Constant of Volcanic Ash Erupted From Five Volcanoes in Japan

The dielectric properties of volcanic ash from five volcanoes in Japan were measured by using the transmission/reflection coaxial line method of a network analyzer, in a frequency range from 3 to 13 GHz. The measured permittivity of powdered ash was then converted to that of solid ash (dense rock equivalent) with the aid of effective medium theory. The values of solid-ash relative permittivities for the five volcanoes revealed that they were in a relatively narrow range. Their real part was generally in a range from five to six in magnitude, while their imaginary part was in a range from 0.08 to 0.18.

Electromagnetic wave propagation in rain and polarization effects

This paper summarizes our study on microwave and millimeter-wave propagation in rain with special emphasis on the effects of polarization. Starting from a recount of our past findings, we will discuss developments with these and how they are connected with subsequent research.

Laboratory measurements of radar depolarization signatures in microwave pulse transmission through randomly distributed spherical scatterers

Laboratory measurements of a backscattered signal for large spherical scatterers are performed to investigate the range of applicability of approximate theory, which the authors used in interpreting the measured depolarization signatures of rain. The measured linear depolarization ratios (LDRs) are in remarkably good agreement with theoretical calculations.

Attenuation and depolarization of millimeter waves due to incoherent scattering in tropical rainfall

Abstract The radiative transfer equation has been applied to investigate the effects of multiple scattering on communication at the millimeter wavelength in tropical rain. Horizontal linearly polarized incident waves are assumed. The scattering characteristics are calculated using the Mie theory at frequencies of 16, 34.8, 82, 140 and 245.5 GHz and at rainfall rates of 12.5, 50 and 150 mm / h . Some results of the directional patterns of the incoherent intensities at various points in the rain medium are presented. The frequency dependence of the propagation distance, attenuation coefficient and the variation of incoherent specific intensities in tropical rainfall are investigated. The incoherent power at the receiver relative to the coherent power, which is important in assessing the quality of signal in the receiver, is also investigated. It is observed that the maximum incoherent copolarized received power is about −28.5 dB in tropical rainfall at 150 mm / h rainfall rate. Also the difference between the copolarized incoherent power in tropical and temperate rainfall is about −3 dB at frequencies higher than 100 GHz , and about −4 dB for the cross-polarized incoherent power components. It may therefore be safely said that multiple scattering may not result in serious degradation of the coherent wave component even in the most intense tropical precipitation. It also appears that it is independent of regional rainfall climatology.

Backscattering enhancement for Marshall-Palmer distributed rains for a W-band nadir-pointing radar with a finite beam width

In this paper, we expand the previous theory to be applied to a generic drop size distribution with spheroidal raindrops including spherical raindrops. Results will be used to discuss the multiple scattering effects on the backscatter measurements acquired by a W-band nadir-pointing radar.