Program, as Progra-m A 2, Pronlern 7.j -U C ill. Descrin-tion of Work( Durine! FY 1.159 :c-,uipmecnr was desi ;ncd, fab-ricated, and uised a determinle the raLm ation atenua~irse propertie s of clear atrro~hcres at cisc Nevada Tes-t Site. In BY 100C the -qui-mient was modified aad measuremc.,tz ode in atusospiirrs with overcast cl'oud conditions at the same :.oeatioi. In IY 961 aire-furtheir equipment nmodificction .rr~easnrrl:"teSr 'were zaeill the Sullmer atm.osnhercit of Lo Anacles ,0 Jaiornia. The measurements wzere made at wavelengths .. 40,, 0.5a, -0.77 and 0.88p (microns) with receiver fields of view up to 64"degrees half-angle. From these data attenuation coefficients were calculated for collimated transmission and aureoled transmission (km source and flat receiver facing the source).-Also calculated for aureoled transmission were values of R, the ratio of "scatteredin" radiation to direct radiation received -y the f lat rcie at various distances from the source. Angular scattering diagrams and attenuation coefficients for scattering were measured for radiation of wavelengths 0.40, 0.451 0.50 and 0.55%1. Relations between these optical characteristics of the atmosphere and meteoro'logical.characteristics such as visibility, relative humidity,, and contaminant contents were examined. Investigations of transmission variabilitywith respect to both time end space were made. Curves wer6 prepared from these and other experimental, data showing transmittances 'of four typical atmospheres as a function of range for the case of flat receivers and radiation from a 4n black body source at 6000 degrees K. 0The Problem:The amount of thermal tadiation delivered to a g ven receiverfrom the fireball of a nuclear explosion depends on the transmittance of the atmosphere as a function of wavelength, the spectral 4istri-.. * butio4 of the radiation, thq receiver field of view, the range, the albedo of the terrain, and the amount and height above the ground of clouds piesentMTh6 purpose of thit experiment was to'determine the. range of transmittance values of the Los Angles nighttime atmoshiI ie during the:months of Aughst and September 1960.-The Findings: 0 A Xenon flaslilamp 4r source and mobile photomultiplier receivers * w th adjustable fields of view and filters are used to determine atteuation coefficients for colllmaed transmisaion and aureoled A * transmission (4U-source and flat receiver and for calculating P,, the ratio of "scaPttered-in" to direct irradlance, at source-r ceiver dis-00 o .tanees ranging from 0.90 to 6 -,77 statute miles.