Abstract: An antenna element such as a monopole, dipole or loop antenna is located in the earth or on the floor of the sea so as to receive pre-earthquake electromagnetic waves generated prior to the occurrence of an earthquake. Unwanted noise waves propagating in the air such as man-made noise are effectively eliminated by a reflector laid on the surface of the earth or by the sea water and only the required pre-earthquake waves are detected by the antenna element, whereby earthquakes can be predicted reliably.

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.