Contains research objectives and summary of research.National Aeronautics and Space Administration (Grant NGR 22-009-131)Sloan Fund for Basic Research (M. I. T. Grant 98

Grams, G. W.

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XII. GEOPHYSICAL RESEARCHResearch StaffDr. G. W. GramsJ. B. ThompsonGraduate StudentsS. J. BlessRESEARCH OBJECTIVES AND SUMMARY OF RESEARCHLaser radar techniques, based on the detection of light scattered from a laser beamby the various constituents of the atmosphere, have been developed by our group to pro-vide remote measurements of atmospheric parameters. Most of this work has been con-ducted as a cooperative effort with Dr. Giorgio Fiocco, of the European Space ResearchInstitute, Frascati, Italy. The results of laser radar observations of mesospheric aero-* 1, 2sols during noctilucent cloud displays have been reported, 2 and analyses of similarobservations by laser radar of the aerosol content of the upper atmosphere continue.Also, G. Fiocco and G. W. Grams have been working on a theoretical model for the spa-tial and seasonal variation of dust in the upper atmosphere; preliminary results of thisstudy have been applied to the problem of interpreting the observed distributions of dustin the upper atmosphere. 3Experiments are also in progress to perform spectral analyses of the light scatteredfrom a laser beam by atmospheric molecules and aerosols. Through the Doppler effectthe random motions of the scattering particles will cause the scattered spectrum to bebroadened with respect to the radiated spectrum. The feasibility of using this techniqueto separate the effects of aerosol scattering from molecular scattering has been demon-strated previously by the use of a pressure-scanned Fabry-Perot interferometer to mea-sure the spectral distribution of the light scattered by naturally occurring aerosols in thelaboratory air and by artificially produced fogs. 4 These experiments are proceeding withan interferometer of greater spectral resolution, with the aim of deriving the tempera-ture of the atmosphere from the observed spectral-line profiles of the scattered light.An investigation of the effect of turbulence and aerosol diffusion on the spectrum of scat-tered laser radiation has recently been completed by John B. DeWolf and the results ofthese experiments have been reported. 5Another laser radar technique is now being considered as a result of recent progressin the development of tunable dye lasers. This technique involves the resonant interac-tion of a laser beam with a particular atmospheric species when the laser has been tunedto coincide in frequency with a resonant transition of that species. Since atomic or16molecular resonance scattering cross sections may be as much as 10 times greaterthan Rayleigh scattering cross sections, minor constituents of the atmosphere can bedetected. A tunable dye laser has been constructed and its performance characteristicsare being evaluated with reference to its use as a radiation source for laser radar mea-surements of the layer of sodium atoms present in the atmosphere at approximately90 km altitude.In addition to the work related to laser radar studies of the atmosphere that is beingThis work was supported principally by the National Aeronautics and Space Admin-istration (Grant NGR 22-009-131), and in part by the Sloan Fund for Basic Research(M. I. T. Grant 98).QPR No. 96(XII. GEOPHYSICAL RESEARCH)conducted by our group, a concurrent investigation of the effects of high pressures insolids is being carried out by Stephen J. Bless. A capacitor discharge driven linearmagnetic pinch is being used to study phase stabilities of materials of geophysical inter-6est, and preliminary results obtained with the apparatus have been reported. Thisdevice utilizes the effects of intense pulsed magnetic fields to produce high pressuresin the material. Irreversible changes in the index of refraction of silica glass have beendemonstrated by pressures as high as 300 kilobars. The apparatus has now been instru-mented to allow measurement of pressure-induced changes in resistivity as a means ofobtaining pressure calibrations.G. W. GramsReferences1. G. Fiocco and G. W. Grams, "Optical Radar Observations of Mesospheric Aerosolsin Norway during the Summer 1966," J. Geophys. Res. 74, 2453-2458 (1969).2. G. W. Grams, "Noctilucent Cloud Studies," Report presented at the Second Confer-ence on Lidar Uses in Atmospheric Research, Brookhaven National Laboratary,Upton, New York, April 1969.3. G. Fiocco and G. W. Grams, "Motion of Aerosols in the Upper Atmosphere," a paperpresented at the Open Meeting of the Cosmic Dust Panel, COSPAR Meeting, Prague,Czechoslovakia, May 1969.4. G. Fiocco and J. B. DeWolf, "Frequency Spectrum of Laser Echoes from Atmo-spheric Constituents and Determination of the Aerosol Content of Air," J. Atmos.Sci. 25, 488-496 (1968).5. J. B. DeWolf, "Homodyne Studies of Light Scattered from a Turbulent Water Jet,"Ph.D. Thesis, M.I.T., Cambridge, Mass., June 1969.6. S. J. Bless, "Production of High Pressures with a Magnetic Pinch," a paper pre-sented at 56th Annual Meeting of the American Geophysical Union, Washington, D. C.,April 1969; Abstract in Trans. Am. Geophys. Union, Vol. 50, No. 4, 1969.QPR No. 96

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