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The effects of optical turbulence on high energy laser propagation have been well documented. The optical turbulence is
typically characterized using the index of refraction structure parameter, Cn2. The value and 3-D variation of Cn2 can be
diagnosed for the surface boundary layer (lowest 50 m of the atmosphere) from values of temperature, pressure,
humidity and wind velocity using meteorological similarity theory. Examples of such similarity theory Cn2 calculators
include the Tunick model for overland applications and the Navy Surface Layer Optical Turbulence (NSLOT) model for
ocean scenarios, both of which are implemented in the AFIT CDE's (Center for Directed Energy) HELEEOS (High
Energy Laser End-to-End Operational Simulation) and LEEDR (Laser Environmental Effects Definition and Reference)
models where they can be assessed from 400 nm to 8.6 m, continuously. The HELEEOS model further allows for the
calculation of the irradiance from within a HEL beam that is scattered by molecules and particulates in the atmosphere to
an off-axis observation point, while incorporating the spreading effects of the turbulence and thermal blooming.
Field and laboratory experiments conducted at Wright-Patterson AFB, Ohio in summer 2009 allowed for validation
measurements for the surface layer optical turbulence and off-axis algorithms to be collected. Turbulence strength
measurements were made at a wavelength of 1.55 μm using a state of the art bistatic turbulence profiler for both
horizontal and vertical paths. Pressure, wind speed, wind direction, relative humidity and aerosol loading data were
collected simultaneously with the Cn2 measurements. As part of the experiment, the profiler's beams were imaged offaxis
with a calibrated camera array and the received irradiance of the
off-axis scattering was quantified.
Characterization of the aerosol distribution along the laser path and the path to the observer is accomplished by
determining the visibility and climatological aerosols for southwestern Ohio. Comparisons between predicted and
measured Cn2 and off-axis irradiance are made. Additionally an experimental technique to derive Cn2 measurements
from weather radar is described and compared to the turbulence profiler data.
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