(1969) is followed for this operation. The steps in this technique are as 

 follows: 



1 . Taking the data from one track at a time, the position of the data 

 points are converted into x, y coordinates and a least-squares straight line is 

 fitted to these locations. Since there is no statistical significance attached 

 to this operation, either x or y may be considered the independent variable. 

 The computer program listed in the appendix considers x, or equivalently 

 longitude, as the independent variable. If the survey tracks happen to run 

 exactly north-south, the program should be modified to consider y as the 

 independent variable. With the coordinates of the data points given as 

 (x., y., i = 1 ,N), the least squares line is f(x) = a_+ a x where 



a 



and 



°1 = 



(? "l) - N °Q 



(13) 



(14) 



2. The perpendicular distance between the straight line and each data 

 point is determined and utilized to project the points orthogonally onto the 

 line with an adjusted data value determined by applying an estimate of the 

 local gradient, assumed to be a function of distance only. If (x ,y, ) are the 

 coordinates, and V, the value of the Kth data point, then the perpendicular 

 distance between this point and the least squares line is given by 



B _ yk-°i\- q o (15) 



B k " I ,2 . J/2 > ' (15) 



(a 1 + 1) 



