@article{Varney2011a, author = "R. H. Varney and M. C. Kelley and M. J. Nicolls and C. J. Heinselman and R. L. Collins", title = "The electron density dependence of polar mesospheric summer echoes", year = 2011 , journal = "J Atmos Sol-Terr Phy", volume = 73, keywords = "amisr, pfisr", doi = "10.1016/j.jastp.2010.07.020" }