DETERMINATION OF THE CHARACTERISTICS OF INVERSION REFLECTING LAYERS IN THE TROPOSPHERE ON CHANGES IN THE SIGNAL INTENSITY ON THE NEAR-EARTH OVER-THE-HORIZON ROUTES IN THE MIDDLE LATITUDES

The methodology for determining changes of altitude, elevation velocity, and reflection coefficient of the elevated inversion layer in the troposphere is examined based on the results of observation of VHF signals on over-the-horizon (OTH) routes. Estimations of the elevation velocity and reflection coefficient of the elevated inversion layers on the results of measuring of the levels of VHF signals in the zone of the near geometric shadow in the middle latitudes and the meteorological sounding data using balloons are obtained.

High-frequency attenuation by a thin high-velocity layer

The Cagniard-de Hoop method is used to investigate elastic-wave tunneling through a thin high-velocity layer. The results indicate high-frequency attenuation in the geometric shadow zone. Attenuation is roughly proportional to layer thickness. Comparison of results obtained by omitting the high-velocity layer but using an average Q operator shows that effects of the high-velocity layer are similar to Q effects, with the equivalent Q for a given layer thickness varying as a function of source-receiver distance. These attenuation effects are explained in terms of deformation of the de Hoop contour.

Numerical Seismograms for Wave Trapping Structures near the Core Boundary

Theoretical amplitudes of diffracted PcP pulses near the geometric edge of the core shadow are important in the determination of earth structure near the core–mantle interface. Frequency domain wave solutions are difficult to apply to earth models with wave-trapping structure near the core. Time domain ray solutions have previously been applied in the illuminated region, and deep in the shadow. A new time domain procedure, including an earth flattening transformation and a ray expansion with the Cagniard–de Hoop ray method, has made it possible to construct numerical seismograms near the geometric shadow edge for a model with a wave-guide structure suggested by seismic array observations at VASA in Alberta.