“…A recent analysis considered a crystal wave guide whose conductivity varied with depth according to a simple algebraic relation [Schwering et al, 1968]; this analysis led to a total attenuation rate of 0.256 db/km at 1 kHz, which is consistent with early calculations of Wait for an exponentially varying conductivity. New measurement techniques were reported [Tsao and de Bettencourt, 1967] mann, 1968a, b;Fung, 1967bFung, , c, 1968aFung, , 1969HagIors, 1967;Valenzuela, 1967Valenzuela, , 1968aLong, 1966]. Although multiple scatter is a strong contributor to depolarized backscatter [Valenzuela, 1967], single-scatter models for backscatter from rough dielectric surfaces also can account for some depolarization /Beckmann, 1968b; Fung, 1967c].…”