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The Air Force Institute of Technology Center for Directed Energy (AFIT/CDE) has developed a first principles atmospheric propagation and characterization model called the Laser Environmental Effects Definition and Reference or LEEDR. This package enables the creation of profiles of temperature, pressure, water vapor content, optical turbulence, and atmospheric particulates and hydrometeors as they relate to line-by-line layer extinction coefficient magnitude at wavelengths from the UV to the RF. Worldwide seasonal, diurnal, and geographical variability in these parameters is accessed from probability density function (PDF) databases using a variety of recently available resources to include the Extreme and Percentile Environmental Reference Tables (ExPERT), the Master Database for Optical Turbulence Research in Support of the Airborne Laser, and the Global Aerosol Data Set (GADS). GADS provides aerosol constituent number densities on a 5º x 5º grid worldwide. ExPERT mapping software allows the LEEDR operator to choose from specific site or regional upper air data to characterize correlated molecular absorption, aerosol absorption and scattering by percentile. The integration of the Surface Marine Gridded Climatology database, the Advanced Navy Aerosol Model (ANAM), and the Navy Surface Layer Optical Turbulence (NSLOT) model provides worldwide coverage over all ocean regions on a 1° x 1° grid. Molecular scattering is computed based on Rayleigh theory. Molecular absorption effects are computed for the top 13 absorbing species using line strength information from the HITRAN 2004 database in conjunction with a community standard molecular absorption continuum code. Aerosol scattering and absorption are computed with the Wiscombe Mie model. Each atmospheric particulate/hydrometeor is evaluated based on its wavelength-dependent forward and off-axis scattering characteristics and absorption effects on laser energy delivered at any wavelength from 0.355 µm to 8.6 m. LEEDR can also produce correlated optical turbulence profiles in percentile format. In addition, probability of cloud free line of sight (CFLOS) for hundreds of land sites worldwide is available in LEEDR. Effects of layers of fog, several types of rain and several types of water droplet and ice clouds can also be considered.In addition to describing some of the underlying theory to the LEEDR calculations, this paper presents graphical results for several different scenarios. These generic scenarios are meant to exemplify how LEEDR enables the physically realistic data capture of atmospheric effects on electromagnetic propagation.

The scattering of a partially-coherent wave from a statistically rough material surface is investigated via derivation of the scattered field cross-spectral density function. Two forms of the cross-spectral density are derived using the physical optics approximation. The first is applicable to smooth-to-moderately rough surfaces and is a complicated expression of source and surface parameters. Physical insight is gleaned from its analytical form and presented in this work. The second form of the cross-spectral density function is applicable to very rough surfaces and is remarkably physical. Its form is discussed at length and closed-form expressions are derived for the angular spectral degree of coherence and spectral density radii. Furthermore, it is found that, under certain circumstances, the cross-spectral density function maintains a Gaussian Schell-model form. This is consistent with published results applicable only in the paraxial regime. Lastly, the closed-form cross-spectral density functions derived here are rigorously validated with scatterometer measurements and full-wave electromagnetic and physical optics simulations. Good agreement is noted between the analytical predictions and the measured and simulated results.

Abstract. The performance of a multibeam laser system is evaluated for coherent and incoherent beam combination under tactical scenarios. For direct comparison, identical aperture geometries are used for both, coherent or incoherent, combination methods. The analysis assumes a multilaser source coupled with a conventional 0.32 m diameter, on-axis, beam director. Parametric analysis includes variations over residual errors, beam quality, atmospheric effects, and scenario geometry. Analytical solutions from previous results are used to evaluate performance for the vacuum case, providing an upper bound on performance and a backdrop for organizing the multitude of effects as they are analyzed. Wave optics simulations are used for total system performance. Each laser in the array has a wavelength of 1.07 μm, 10 kW (25 kW) output power, and Gaussian exitance profile. Both tracking and full-aperture adaptive optics are modeled. Three tactical engagement geometries, air to surface, surface to air, and surface to surface, are evaluated for slant ranges from 2.5 to 10 km. Two near-median atmospheric profiles were selected based upon worldwide climatological data. The performance metric used is beam propagation efficiency for circular target diameters of 5 and 10 cm. © 2012 Society of Photo-Optical Instrumentation Engineers (SPIE).