DESCRIPTION OF TERMS 



This informal glossary is included to aid readers who represent 

 diverse backgrounds in geology, geophysics, acoustics, statistics, and 

 other fields. The descriptions of terms, phrases, and acronyms included 

 are intended to reflect their use within this report, rather than a 

 general or rigorous definition. 



Amplitude 



The departure of a periodic function from its mean. 



Anisotropy 



Condition of having different properties in different directions. 



Band-limited 



Condition in which a signal contains a finite range of frequency. 

 With reference to Fourier analysis, this band ranges from the fun- 

 damental frequency to the Nyquist frequency. 



Boxcar function 



A function which equals unity over some finite length and zero 

 everywhere else. The multiplication of this function with an infi- 

 nite series represents mathematically the sampling of a finite 

 series from an infinite process. Sometimes called a rectangle 

 function. 



Ch1-square distribution 



The probability distribution for the estimation '^rror of the 

 power spectrum. Due to the form of the distribution, the errors 

 associated with the amplitude spectrum appear constant when plotted 

 on log-transformed axes. 



Coherent signal 



A signal in which the phase relationship of the various frequency 

 components is retained. 



Convolution 



A mathematical operation which is equivalent to multiplication in 

 the opposite transform domain. 



Deterministic model 



A numerical model in which the mathematical parameters represent 

 specific measurable quantities of the process under study. 



Ensemble average 



The mean value of a group of repetitive samplings for a given sta- 

 tistical measure. 



FFT 



Fast Fourier Transform. A numerical algorithm for estimating the 

 Fourier transform with a greatly reduced number of operations. 



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