cal description of the backscattered return. According to 

 the Central Limit Theorem, this will approximately apply 

 (Independent of the sea-surface statistics) If the foot- 

 print diameter Is large compared with the correlation scale 

 of the scatterers — a condition which Is often satisfied 

 In satellite applications. However, an Interesting tech- 

 nique exploiting non-Gaussian properties of backscattered 

 modulated microwaves [48] Is mentioned In §8. In this case 

 the non-Gaussian signature, although small, can be readily 

 filtered out of the much larger Gaussian components. Useful 

 sea-state Information can also be obtained from the Initial 

 return characteristics of altimeter pulses, which corre- 

 spond to the non-Gaussian, small footprint limit (§9). 

 The non-Gaussian properties of these signals have not been 

 systematically investigated, but a preliminary inspection 

 indicates that they are related to useful wavelength dis- 

 tributions of the wind-sea not contained in the second 

 moments of the signal. 



A backscattered mlcrowa-<;-e pulse centered at the fre- 

 quency b^Q may be expressed in the form 



v(tiT) = B(tiT)ei^ot 

 where B(tiT) is a random complex modulation factor 

 (complex envelope) depending on the delay time t relative 

 to the time of emission T of the pulse. For fixed T , 

 B(t) defines the shape of the backscattered pulse, the 



25-29 



