\def\beq{\begin {equation}}
\def\eeq{\end {equation}}
\def\beqa{\begin {eqnarray}}
\def\eeqa{\end {eqnarray}}

\def\data{\bf d}
\def\model{\bf m}
\def\zero{\bf 0}
\def\xvar{\bf x}
\def\pvar{\bf p}
\def\lop{\bf L}
\def\zero{\bf 0}
\def\iop{\bf I}
\def\reg{\bf A}
\def\prec{\bf A^{-1}}
\def\time{\bf t}
\def\tomo#1{\bf T_{#1}}
\def\slow#1{\bf s_{#1}}
\def\ds{\bf \Delta s}
\def\dt{\bf \Delta t}
\def\pox{&\approx&}

\def\vmap{v_{m}}
\def\vfoc{v_{f}}
\def\smap{s_{m}}
\def\sfoc{s_{f}}
\def\part{\partial t}
\def\parx{\partial x}
\def\parxp{\partial x'}
\def\parz{\partial z}
\def\partau{\partial \tau}
\def\ztomo{\left({\bf T_{z,ref}}-{\bf T_{z,ray}}\right)}
\def\sref{s_{\rm ref}}
\def\tautomo{\left({\bf T_{\tau,ref}}-{\bf T_{\tau,ray}}\right)}

\def\smf{S_m(z,x,y)}

\def\mv{{\bf \vec m}}
\def\hx{x_h}
\def\freq{\omega}
\def\DSR{{\rm DSR}}