approximately the same magnitude but of opposite signs. Thus, terms 

 involving the products [1] [2] and {2] {3] tend to cancel. Letting 

 ^1 ~ "^2 — ^ ^ - ^ ' 



b^j sin kQ,j sin 2tt6 - 2 cos k^j sin^ irS 

 a^j ~ cos k^j sin 2Tr6 + 2 sin kfi^- sin2 irS * 



Using the trigonometric identities for the double arc, this expression 

 reduces to : 



— ^ = tan (_ka^- - T\&) . (C-19) 



^' '^ 



Phase differences between locations will be approximately correct. 



53 



