A method for the high resolution spectroscopy of rotating planets is discussed which in principle (1) uses all the light from the planet, (2) is not limited in its resolution by the rotation of the planet, (3) can produce spectra in which the only sharp lines present must be of planetary origin, (4) retains spatial resolution in latitude, and (5) uses only conventional coudé spectrograph equipment. Although it is not possible to take full advantage of all these gains with presently available gratings, a significant improvement over present techniques is still possible.
T. J. Deeming and L. M. Trafton, "High Resolution Spectroscopy of Rotating Planets," Appl. Opt. 10, 382-385 (1971)