considered to be of the form 



<11-1) "ifk = ■njk(true) +^jk 



where t]^ is the tabulated value; ""li^/true) ^^ ^^ true value and e jj^ is 



a random error picked according to sorae probability scheme to be discussed in 



detail later« 



The values of e jj^ will turn out to be appreciable, and they have the effect 

 of making the pattern shown fuzzy in detail. Due to the size of e ., , statistical 

 evaluations of the patterns shown should be interpreted with considerable caution. 



There are other errors of a more serious nature in the data as shown in 

 figures 11.4 and 11„5. These errors will be analyzed in the following para- 

 graphs of this part of the report. 



The covariance surfaces 



The covariances were computed according to the equations given in Part 8 

 and plotted on a square grid of points 41 points on a side. The covariance sur- 

 face for Data Set 2 is shown in figure 11.6, the surface for Data Set 3 is shown 

 in figure 11.7, and the average of the two is shown in figure 11.8. The units of 

 the contours are (mm)^ x 100. Shaded areas are negative. The figures show 

 an estimate of the correlation (when each value is divided by the value at the 

 center) of the sea surface with itself over distances of the order of 600 feet 

 in any direction. Roughly the correlation is less than ±0.10 in any direction at 

 a distance of 600 feet. Again the effects of errors in the data have distorted 

 the pattern. The covariances would have the dimensions of (ft) , if each 



number shown were divided by (10016)"^^ 



157 



