The zeroth order operator

The zeroth order operator has the form

$$\left[ \begin{array} {ccccc} \cos(\phi)/2 & & \sin(\phi)/2 ... ...phi)/2 & & 0 \\ & & & & \\ 0 & & 0 & & 1/2\end{array}\right].$$

This is the familiar source and receiver rotation operator described by Alford(1986).