HEAD WAVES IN TWO-DIMENSIONAL SEISMIC MODELS*

Studies made on head waves in a large number of two-dimensional horizontal and inclined layer seismic models are described. The assumption that the amplitude of head wave decreases exponentially with distance is found to be valid in horizontal layers. For the correct estimation of the head wave decay coefficient, the decrease of amplitude due to the divergence of wave energy should always be considered. The variations of head wave amplitude at large distances from the source appear to follow the theory of Heelan (1953). It is, however, concluded that the theory can only be verified from the measurements in models which have large velocity contrast and thick layer at the top. A prominent interference phenomenon between the direct and head wave has been observed near the critical distance. This is more marked for up-dip profile in the case of inclined layer models. The rate of head wave amplitude decrease with distance beyond the zone of interference is found to depend on dip angle, direction of the dip, and velocity contrast.     

Study of spectral reflectance characteristics of an urban environment — Case study of Kanpur city

Spectral reflectance Studies have been carried out on various features (man-made as well as natural) with reference to urban environment using a portable spectro-radiometer in wavelength regions ranging from 0.45 to 1.0 μm of Kanpur city and its surrounding areas. The signature values, thus collected, were used to draw spectral reflectance curves of each feature separately and to determine/select the optimum wavelength regions suitable for urban area studies. It has been observed that the best band width suitable for urban feature discrimination are between 0.45 to 0.55 μm (blue region) & 0.69 to 0.80 μm (near-infrared region) of the spectrum.