Abstract: An open resonator comprises two concave spherical reflectors or one spherical and one plane reflectors positioned so as to form a resonant structure and each being provided at an electromagnetic coupling region thereof with a large number of conductor stripes disposed in parallel at a spacing sufficiently small in comparison with the wavelength of an incident electromagnetic wave. The diameter of the circular coupling region can be made very large in comparison with the wavelength. An ultra-high Q value can be obtained with the open resonator with very high excitation efficiency to a resonator mode. The Q value of the open resonator can be varied with the angle between the directions of the conductor stripes of the two reflecting mirrors.

Abstract: The probability of a volcanic eruption is predicted by simultaneously receiving long-wave radiation signals from magma at at least four points in the vicinity of the magma, cross-correlating the received signals to detect time lags among the signals, calculating the site, magnitude and shape of the magma from the time lags, and judging the likelihood, time, scale and site of a volcanic eruption from time-course changes in the calculated site, magnitude and shape of the magma.

Abstract: A method for detecting earthquakes comprises the steps of picking up pre-earthquake long waves or earth currents at four or more observation points located underground or at the sea bottom, carrying out a computation based on the interrelation among the so-obtained= signals to obtain the three-dimensional distribution of the sources and intensities of the long waves or earth currents, and predicting the focal region, scale and time of occurrence of earthquakes from the time-course variation in the so-obtained three-dimensional image of the wave source.

Abstract: A multi-level quadrature amplitude modulator system that can be used in communication channels in which there is intense fluctuation has a transmitter section that is provided with a frame synchronizer that inserts a reference symbol into each group of message symbols, and a receiving section that is provided with an estimator for the transmission path distortion in the message symbols on the basis of distortion found in the reference symbols. The receiving section is also provided with a compensator for the distortion thus described.

Abstract: A system for measuring height distributions of atmospheric temperature and wind velocity (wind direction and wind speed) utilizes the facts that a sound wavefront in the atmosphere constitutes part of an ellipsoidal surface and that there always exists a normal which passes through an interior point of the ellipsoid. The Doppler radar is capable of measuring a height distribution of wind velocity on the basis of Doppler frequencies of scattered waves produced by the atmospheric turbulence. The radar and generator are arranged on a straight line in the wind direction so that a radio wave from the radar is directed to the wavefront of a sound wave from the generator. The radar antenna beam is scanned so that it perpendicularly intersects the sound wavefront. The speed of the sound wavefront is measured from the Doppler frequencies of reflected waves. The sound speed is obtained by removing the wind speed component from the measured speed of the sound wavefront.