ynon, W.J.G. (1940), (1947) The application ative European Project 'COST 210' (Influence of the Atmosphere of ionospheric data to radio communications, Proc. Phys. Soc. on Interference Between Radiocommunication Systems at Frequen- 52. 518 and 59. 58. cies Above 1GHz). The full report should be consulted for details of Appleton, E.V. and Piggott, W.R. (1954) Ionospheric absorption the procedures developed. measurements during a sunspot cycle, J. Atmosph. Terr. Phys. 5. Bailey, D.K. (1964) Polar cap absorption, Planet. Space Sci. 12. Techniques for studying tropospheric structures Bailey, D.K., Bateman, R. and Kirby, R.C. (1955) Radio trans- mission at VHF by scattering and other processes in the lower The importance of a knowledge of the structure of the troposphere ionosphere, Proc. IRE, 43. 1181. in studies of propagation is clearly evident in the above sections. Baker, D.M. and Davies, K. (1968) Waves in the ionosphere pro- The small-scale variations in refractive index and in the intensity of duced by nuclear explosions, J. Geophys. Res. 73. 448. precipitation are two important examples. They form part of the Baker, D.M. and Davies, K. (1969) F2-region acoustic waves from general topic of tropospheric probing. severe weather, J. Atmosph. Terr. Phys. 31. 1345. Much useful information on the height-variation of refractive Bean, B.R. and Dutton, E.J. (1966) Radio meteorology, Monograph index can be obtained from the radio-sondes carried on free balloons 92, US Government Printing Office, Washington. and used in world-wide studies of meteorological structure. How- Bello, P.A. (1965) Some techniques for instantaneous real-time ever, for many radio applications these devices do not provide measurements of multipath and Doppler spread. IEEE Trans. sufficient detail. To obtain this detail instruments called refrac- Comm. Tech. 285. tometers have been developed, mainly for use in aircraft, on captive Belrose, J.S. and Burke, M.J. (1964) Study of the lower ionosphere balloons or on tall masts. They generally make use o