It is immediately apparent that the reflectivity of icebergs is indeed poor 

 as the same ratio for a flat metal plate is equal to 1,200. 



The reflection coefficient (ratio of reflected energy to incident energy) 

 can be computed as follows. The effective echo area is proportional to the 

 power ratio as seen from equation (7). But the power ratio is proportional 

 to the square of the field intensity; therefore, we can write: 



Ai I Ri 



ft, 



(9) 



A, 



where R, and R m are the reflection coefficients of the real and idealized 

 icebergs, respectively. Taking into account the average aspect reflection 

 for the model conducting iceberg ami the Grand Banks icebergs, and 

 substituting 1.0 for R,„, equation (9) becomes 



72 = 0.33 



where R is the average reflection coefficient of Grand Banks and North 

 Atlantic Ocean iceberg ice. Confidence in the arguments used to arrive 

 at this coefficient is given by its close agreement with the theoretical 

 values of 0.25 for a dry iceberg and 0.32 for a melting iceberg derived 

 below. 



Theoretical Reflection Coefficient 



As has been shown the computed reflection coefficient from various 

 arguments based on field observations is 0.33. It remains to compute the 

 reflection coefficient based on theoretical considerations. Either by con- 

 sideration of Fresnel's equations or the intrinsic impedance derived 

 therefrom, the reflection coefficient at normal incidence becomes 



/~r y /- =R= y^y ( 10 



where e is the dielectric constant, Z the intrinsic impedance, and A' the 

 reflection coefficient modulus. The electromagnetic properties of a 

 medium are completely described by the complex dielectric constant: 



e c = e r -je;= e r -2j- = (n-jt) 2 (11) 



where 



e,. = the complex dielectric constant or complex relative permittivity 

 K = conductivity in electrostatic units 

 /= frequency in cycles per second 

 n — refractive index 

 f = absorption coefficient 



63 



