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Unified sensor for atmospheric turbulence and refractivity characterization


TECHNOLOGY AREA(S): Sensors, Electronics, Battlespace 

OBJECTIVE: Develop and demonstrate a compact electro-optics system capable of in-situ characterization of atmospheric turbulence and refractivity along the path to a space- or ground-based target without using an adaptive optics system. 

DESCRIPTION: Simultaneous evaluation of laser beam irradiance characteristics at a target along with the line-of-sight sensing of atmospheric turbulence and refractivity effects is essential for the ongoing development of Air Force surveillance and directed laser energy systems. There is a growing need for remote in-situ evaluation of atmospheric turbulence, refractivity and laser beam characteristics (irradiance distribution, scintillations, beam footprint, beam wander, etc.) along the path to space or ground-based targets. This characterization should be performed by a sensing system, which utilizes for its operation solely the optical waves scattered off the target - target-in-the-loop (TIL) sensor. This implies that the target is passive in the sense that it does not contain any on board sensors. The TIL sensor may use multiple wave lengths for refraction modeling. The TIL sensor should provide currently non-existing capabilities for simultaneous characterization of atmospheric turbulence and refractivity effects which are especially important for observation of space objects at low elevation angles and long ranges (< 15 degrees in elevation and 2,000 km, and 100 km ground based targets) for surveillance. Sensor design needs to be capable of measuring atmospheric parameters consistent with the models described in References 3. 

PHASE I: Develop a TIL-based sensor system concept. Using wave-optics numerical simulations at two or more wavelengths, demonstrate technical feasibility of the proposed approach and evaluate expected accuracy of laser beam and atmospheric turbulence and refractivity characterization. The analysis should account for aberration factors and includes photon budget and signal-to-noise ratio evaluation. 

PHASE II: Complete opto-mechanical design of the sensor prototype. Select optical and electronic components. Integrate system prototype. Develop sensing and data processing software. Perform the sensor prototype atmospheric evaluation with a stationary target over at least 10 km distance for horizontal paths and/or at 2000 km at 20 degrees elevation for space targets. Compare predictions and test results; identify differences and their causes. 

PHASE III: Develop and demonstrate, over long (>100k m is preferred, 60 km is acceptable) ranges a ground-based targets and/or 2000 km range at 20 degrees elevation for space targets, an atmospheric sensing system capable of continuous monitoring of laser beam and atmospheric characterization along the dynamically changing line of sight to the space or/and ground based targets. 


1. Valerie Coffey, High-Energy Lasers: New Advances in Defense Applications, Optics & Photonics News, vol. 25, no. 10, pp. 28-35, 2014.

2. M. A. Vorontsov, Speckle effects in target-in-the-loop laser beam projection systems, Adv. Opt. Techn., vol. 2, no. 5“6, pp. 369“395, 2013.

3. Papers published in the Topical Conference of Optical Society of America, Propagation through and characterization of Deep Volume Turbulence, 2013-2014.


KEYWORDS: Atmospheric Sensing And Characterization, Active Sensors, Scintillometer, Directed Energy 

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