1. Ai, Y., S. Lu, X. J. Zhang, and S. S. Gong, Characteristics of the sodium layers observed by the laser radar at Wuhan, China J. Chinese Laser, No. 5, 56-59, 1998.
2. Beatty, T. J., C. A. Hostetler, and C. S. Gardner, Lidar observation of gravity waves and their spectra near the mesopause and stratopause at Arecibo, J. Atmos. Sci., 49, 477–496, 1992.
3. Gardner, C. S. and D. G. Voelz, Lidar studies of the nighttime sodium layer over Urbana, Illinois 2. Gravity wave, J. Geophys. Res., 92, 4673–4694, 1987.
4. Gong, S. S., X. Z. Zhen, X. J. Xue et al., The first observation of sodium layers by laser radar at Wuhan in China, Science in China (Series A), 27(4), 369–373, 1997.
5. Liu, C. H., World Ionosphere/Thermosphere Study Handbook, pp. 155–162, Volume 2, Chapter 6, University of Illinois, 1989.