Geometrical optics in nonstationary media

Summary form only given. To establish the basic equations of geometrical optics in inhomogeneous and nonstationary (time-varying) media it is advantageous to combine the three spatial coordinates and the time to four-dimensional space-time coordinates. The restriction to Minkowski coordinates (for a "flat" space-time) is not necessary and would restrict the applications to plane-stratified media. Therefore curvilinear spatial coordinates are employed. The four-dimensional propagation vector is comprised of the customary spatial propagation vector and the circular frequency.