is Indeed limited only to the pulse onset (and the second 

 corner terminating the linear ramp in the square-pulse 

 case) or whether the entire pulse is affected. If the 

 wave signature is restricted to the pulse corners, it can 

 be largely eliminated from the mean surface measurement 

 by extrapolation of the linear regime; if not, a correction 

 must be applied to the entire pulse^and its magnitude can 

 be computed only if the wave field is known. 



According to the specular reflexion model, the mean CW 

 power reflected vertically from an infinitesimal area dA 

 is given by 



dl = 6 P (n) ^dA 



2 



5^n=0"^ (4) 



where 6 is a geometrical constant and P (n) the 

 probability distribution of facet slopes n = f ^-— i 53^) 



In the case of a step-function pulse, power is received 

 at the delay time t, only if the reflecting facet lies 

 within a sphere of radius R = ct,/2 . from the source, or 



in terms of the penetration time tp and footprint dia- 



1 

 meter r = (2hctp) ^ , if the surface displacement 



C > C(r', tp) = (r' -r2)/2h 



where r' is the radial distance of the element dA from 

 the foot of the surface normal passing through the source. 

 Thus the expression (4) must be replaced in this case by 



i 



dl = 6 I P (?,n)dCdA 



25-46 



