Röttger, J., Rietveld, M. T., La Hoz, C., Hall, T., Kelley, M. C., & Swartz, W. E. (1990). Polar mesosphere summer echoes observed with the EISCAT 933-MHz radar and the CUPRI 46.9-MHz radar, their similarity to 224-MHz radar echoes and their relation to turbulence and electron density profiles. Radio Science, 25, 671-687.