Figure 4-1 Schematic niustration of the scale dependence of station- 

 arlty. All traces are derived from the same function (B), 

 however the inferred stationarity of the mean would be dif- 

 ferent depending upon the scale of observation. Observed 

 at the scale of frame A, the mean is obviously non-station- 

 ary. However, the mean appears stationary at the larger 

 scale of B or the smaller scale of C. In most natural sys- 

 tems, the non-stationary components occur in the partially 

 resolved low spatial frequencies. This difficulty can be 

 handled analytically by defining homogeneous provinces on 

 the basis of stationarity and prewhitening of the spectra. 



18 



