In general, laser radiation is attenuated as it propagates through the atmosphere. In addition, the laser beam is often broadened, defocused and may even be deflected from its initial propagation direction. These atmospheric effects have far-reaching consequences for the use of lasers in optical communication, weaponry, target designation, ranging, remote sensing, and other applications which require transmission of laser beams through the atmosphere.

A review is presented of low resolution models for the calculation of slant path atmospheric transmission in the infrared, visible, and ultraviolet regions. It purports to summarize, for the benefit of readers who are optical designers or of users whose systems operate in the atmospheric envjronment, the fundamentals of atmospheric transmission and modeling. The discussion primarily revolves on the attenuation effects modeled in widely-adopted codes, such as LOWTRAN and EOSAEL.

The theoretical studies of the transmission of electromagnetic radiation through large fires have been generally postulated as either uniform conditions horizontally across the rising products of combustion or, at best, some assumed, easily formulated inhomogeneity in order to make the mathematics more tractable. In a previous paper the authors presented a new logical approach to the treatment of time-dependent processes, the Sequential Process Method in which complex time-dependent processes are broken down into a chronologic sequence of sub-processes each assumed, during one cycle of events, to be occurring during the same time step. The method we elucidated by applying it to a rather simple physical picture, that of radiating symmetric concentric sleeves over a uniformly burning, flat circular fire. In this work the physical picture is extended to include non-uniform, radially symmetric, large flat fires, and the method of transport between sleeves has been generalized. An improved method of accounting for the behavior at the interface of two distinct gas volumes is proposed, and the effects of application of such procedures are illustrated. Velocity and temperature profiles calculated suggest the need for theoretical study of diffusion processes not considered in current fire kinetic studies, including the inclusion of an outer plume "sleeve" which was initially part of the ambient. Recommendations are given for future research in fire kinetics which would explain effects of wind and temperature gradients in the atmosphere, the distribution of particulates in the fire plume, and describe a fire as a source of long-term obscurants.

A 10-11 cm aperture stellar scintillometer can measure atmospheric isoplanatic angles reliably provided the normalized variance and the zenith angle of the data are sufficiently, restricted. Within these constraints, the normalized variance data has a zenith angle power law that is quite close to the theoretical prediction. This is a self-consistent indication that the instrument is actually measuring the isoplanatic angle.

The transverse coherence length (r0) was directly measured approximately every 5 minutes from 29 August to 28 September 1984 at HIDL, WSMR. An MTF-device was used with stellar sources for the ro observations. The diurnal variation of ro is discussed and related to processes affecting optical turbulence in the planetary boundary layer. A complete heat exchange study involving radiative, sensible heat, latent heat and soil heat fluxes is presented and related to ro values as well as to surface measured Cn2 . Of particular n interest to the problem is the observed surface thermal activity. Vertical profile measurements of Cen, obtained from th.ermosondes at various times of the day and night, are presented to show the contributions of optical turbulence at various levels in the atmos-phere to r_o. C2n development as related to solar activity is discussed. The measured Cn2 profiles are compared to appropriate models.

We have obtained optical turbulence profiles consisting of values for the statistical parameter Cn-squared derived from stellar scintillations. Each profile consists of the values for Cn-squared determined for a collection of seven vertical positions (2-20km). These determinations are based upon measurements comprising the spatial spectrum of intensity scintillations observed across wavefronts arriving from a given star during a two-minute period of time. The profiles in this data base were obtained from two different locations over a period of several years; 1) CAOTF] Advanced Optical Test Facility at Verona, New York; 2) [AMOS] ARPA Maui Optical Station at Maui, Hawaii. We have time-analyzed the statistical fluctuations in the Cn-squared values obtained. This analysis has revealed that the turbulence fluctuations are statistically homogeneous for only relatively short periods of time. We shall report on several systematic changes in the statistical properties which we have found to occur over longer periods of time.

Two Atmospheric Boundary Layer (ABL) models, the Kukaharets/Tsvang and the Kaimal models are used to obtain Cn² profiles during daytime conditions for comparison with balloon-borne thermosonde measurements. Path averaged Cn2 measurements obtained on a 14 meter tower are used as inputs to the models. Values of ro2(coherence length) and Oo (isoplanatic angle) are calculated by integration of model expressions for Cn2 as a function of altitude. The VanZandt mode is used to obtain ro and go contributions from above the ABL. These are compared to values obtained by integration over the thermosonde Cn2 height profiles. Comparisons are also made to isoplanometer and MTF device measurements made near the ground.

A measurement program, jointly conducted by the Army's Atmospheric Sciences Laboratory (ASL) and the Air Force Geophysics Laboratory (AFGL) was undertaken at the High Energy Laser Instrumentation Development Laboratory (HIDL), White Sands Missile Range (WSMR) site, between 29 August and 28 September 1984. During this 31 day test period, meteorological and turbulence data were acquired 24 hours per day, seven days per week. A large data base of surface and tower measurements of wind, temperature, turbidity, heat fluxes, etc. and measurements of upper atmosphere turbulence, temperature, density, and humidity now exists. The purpose of this program was to characterize the optical turbulence and obtain cloud cover and distribution statistics in the general area of the HIDL test site. An overview of the test, representative data, and the data base is described.

Atmospheric turbulence below 300 meters has been probed with an Echosondel acoustic sounder at the Mauna Kea, Hawaii observatory. Continuous hourly averages for several months yield "characteristic" site profiles of Cn2 and Cn2 with altitude as well as the diurnal signatures. Near surface acoustic turbulence soundings are compared to the results of observations using microthermal probes at the NOAA Boulder Atmospheric Observatory in Colorado and at Mt. Livermore near McDonald Observatory in Texas.