The study of tropospheric refractive index distributions which began in 1951 using an airborne microwave refractometer has been continued during the past year with emphasis being placed on obtaining data on the microstructure of the atmosphere. Refractometers sufficiently sensitive to observe refractive index or equivalent moisture content variations having frequencies up to 100 cycles per second and amplitudes as small as 0.01 N-unit have been used in aircraft over New England, Florida, Ohio and Colorado areas to measure refractive index fluctuations from near the surface to up to 20,000 feet. Special efforts have been made to obtain data on free air and air to cloud index changes and a summary of certain of these data is presented. Preliminary analyses are made of data showing flights through clouds, convective thermals and frontal systems.
* The research reported in this paper was conducted primarily under the auspices of Contract AF 19 (604)-494 with the Air Force Cambridge Research Center.
** The University of Texas.
*** Air Force Cambridge Research Center.