In MTW Gravitation, the shortwave approximation on gravitational waves in a curved background is given in Section 35.13. This treatment is similar to the WKB approximation in quantum mechanics, or the geometric optics in electromagnetism. The authors pointed to two more rigorous treatment.
One of them is Y. Choquet -Bruhat's work Commun. Math. Phys. 12, 16 (1969). Unfortunately, I only read Chinese and English. Is there any translated version?
The second reference is referred as "MacCallum and Taub (1973)", but the author did not actually any information on this reference in the Bibliography. Do you know what it is?