Three-dimensional optical turbulence assessments from doppler weather radar for laser applications

The ultimate goal of this study is to expand the spectral range of surface layer optical turbulence (C_n²) models from their present valid range in the visible and infrared to a much broader 400 nm to 8.6 m spectral range. An immediate benefit of such a spectral expansion would be the capability to convert radar-measured C_n² to laser wavelength C_n², and then use radar-derived optical turbulence to improve free space laser and high energy laser applications. The experimental technique developed is compared to and validated against field test data. The field tests compare National Weather Service radar data to C_n² measurements obtained from scintillometers, range-gated experimental turbulence profilers, and surface layer turbulence deduced from similarity theory. The field tests were conducted at Starfire Optical Range (SOR), the High Energy Laser Systems Test Facility (HELSTF), and Wright-Patterson AFB. This research shows that 3-D fields of optical turbulence, C_n², can be deduced from operational Weather Surveillance Radar 88-D Next Generation (WSR-88D NEXRAD) clear-air volumetric reflectivity scans. This is accomplished by relating turbulence backscattering characteristics to C_n² equations for radar. The C_n² fields deduced from radar are converted to wavelength-specific C_n² values using a 400 nm to 8.6 meter anomalous dispersion index of refraction calculator coupled with a wind speed and terrain effects spectral modulator function. Thus 3-D fields of C_n² values within the atmospheric boundary layer for visible and infrared wavelengths can be obtained from widely available internet reflectivity scans from weather radars. Range-gated radar results are compared to range-gated turbulence profiler measurements.