Design, Development, and In-flight Testing of a Pointer/tracker for In-flight Experiments to Measure Aero-optical Effects over a Scaled Turret

We address the design, development, and testing of a pointer/tracker as a probe beam for the purpose of making high-speed, aero-optical measurements of the flow over a scaled beam director turret. The tracker uses retro-reflection of the probe beam off of a Reflexite annulus surrounding the turret. The constraints of the design required a near-total-commercial off the shelf system that could be quickly installed and removed in a rented aircraft. Baseline measurements of environmental vibrations are used to predict pointing performance; mitigation of line-of-sight jitter on the probe beam is achieved through passive isolation and the design of relay optics. Accommodation of ambient light is made with the use of wavelength filters and track algorithms. Postanalysis of measured data is compared to design estimates

Worldwide Assessments of Laser Radar Tactical Scenario Performance Variability for Diverse Low Altitude Atmospheric Conditions at 1.0642 μm and 1.557 μm

Spatial, spectral and temporal variations in operating conditions are major contributors to the expected variability/uncertainty in system performance. The ratio of signal-to-noise ratio (SNR) based on climatological data to a standard atmosphere is the primary performance metric used, with results presented in the form of histograms and maps of worldwide LADAR performance variation. This metric is assessed at 2 wavelengths, 1.0642 μm and 1.557 μm, for a number of widely dispersed land and maritime locations worldwide over oblique and vertical air to surface paths in which anticipated clear air aerosols and location specific heavy rain and 150 m thick fog occur.Abstract excerpt © SPI

Worldwide Uncertainty Assessments of Ladar and Radar Signal-To-Noise Ratio Performance for Diverse Low Altitude Atmospheric Environments

In this study of atmospheric effects on laser ranging and detection (ladar) and radar systems, the parameter space is explored using the Air Force Institute of Technology Center for Directed Energy\u27s (AFIT/CDE) High Energy Laser End-to-End Operational Simulation (HELEEOS) parametric one-on-one engagement level model. The expected performance of ladar systems is assessed at a representative wavelength of 1.557 µm at a number of widely dispersed land and maritime locations worldwide. Radar system performance is assessed at 95 GHz and 250 GHz. Scenarios evaluated include both down looking oblique and vertical engagement geometries over ranges up to 3000 meters in which clear air aerosols and thin layers of fog, locally heavy rain, and low stratus cloud types are expected to occur. Seasonal and boundary layer variations are considered to determine optimum employment techniques to exploit or defeat the environmental conditions. Each atmospheric particulate/obscurant/hydrometeor is evaluated based on its wavelength-dependent forward and off-axis scattering characteristics and absorption effects on system interrogation. Results are presented in the form of worldwide plots of notional signal to noise ratio. The ladar and 95 GHz system types exhibit similar SNR performance for forward oblique clear air operation. 1.557 µm ladar performs well for vertical geometries in the presence of ground fog, but has no near-horizontal performance under such meteorological conditions. It also has no performance if low altitude stratus is present. 95 GHz performs well for both the fog and stratus layer cases, for both vertical and forward oblique geometries. The 250 GHz radar system is heavily impacted by water vapor absorption in all scenarios studied; however it is not as strongly affected by clouds and fog as the 1.557 µm ladar. Locally heavy rain will severely limit ladar system performance at these wavelengths. However, under heavy rain conditions ladar outperforms both radar systems. © 2013 SPI

Modeling Bistatic Spectral Measurements of Temporally Evolving Reflected and Emitted Energy from a Distant and Receding Target

The Air Force Institute of Technology\u27s Center for Directed Energy developed the High Energy Laser End-to-End Operational Simulation (HELEEOS) model in part to quantify the performance variability in laser propagation created by the natural environment during dynamic engagements. As such, HELEEOS includes a fast-calculating, first principles, worldwide surface-to-100 km, atmospheric propagation, and characterization package. This package enables the creation of profiles of temperature, pressure, water vapor content, optical turbulence, atmospheric particulates, and hydrometeors as they relate to line-by-line layer transmission, path, and background radiance at wavelengths from the ultraviolet to radio frequencies. In the current paper an example of a unique high fidelity simulation of a bistatic, time-varying five band multispectral remote observation of energy delivered on a distant and receding test object is presented for noncloudy conditions with aerosols. The multispectral example emphasizes atmospheric effects using HELEEOS, the interaction of the energy and the test object, the observed reflectance, and subsequent hot spot generated. A model of a sensor suite located on the surface is included to collect the diffuse reflected in-band laser radiation and the emitted radiance of the hot spot in four separate and spatially offset midwave infrared and longwave infrared bands. Particular care is taken in modeling the bidirectional reflectance distribution function of the delivered energy/target interaction to account for both the coupling of energy into the test object and the changes in reflectance as a function of temperature. The architecture supports any platform-target-observer geometry, geographic location, season, and time of day, and it provides for correct contributions of the sky-earth background. The simulation accurately models the thermal response, kinetics, turbulence, base disturbance, diffraction, and signal-to-noise ratios.Abstract © SPIE