1(R) The ratio of the amplitude of a reflected ray (A1) to that of the incoming ray (A0), such that R = A1A0. In the case of a normally incident ray, R can be expressed in terms of the acoustic impedances of the two media above and below the reflector, Z1 and Z2, so that R = (Z2 – Z1)/(Z2 + Z1). The range of values for R lie between -1 and +1. If R is negative a phase reversal (π) in the wave occurs at the reflector. For water/air R has a typical value of -1; for rocks R has an average value of 0.2 or less. See also transmission coefficient. The reflection coefficient can also be expressed in terms of energy (R΄), when R΄ = R2.
2 (k) A ratio of true resistivities, such that k = (ρ2 – ρ1)/(ρ2 + ρ1), where ρ1 and ρ2 are the true resistivities above and below an interface.
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