Tomographic Coherent Ladar Based Atmospheric Turbulence Profile Characterization System

ABSTRACT:Under this Phase II SBIR contract, Bridger Photonics and Montana State University-Spectrum Lab will design, build and deliver both a statistical scintillation tomographic system and a coherent tomographic wavefront sensor (CTWS). Both proposed systems meet the long term Air Force needs with respect to the full characterization of atmospheric turbulence along horizontal or slant paths. The statistical scintillation system will use tomographic methods to spatially resolve the turbulence statistics using sets of scintillation measurements. This system has utility as a general scientific device and will enable a deeper understating of atmospheric turbulence. The CTWS will use coherent digital holography images from diverse viewpoints of targets of opportunity and ultimately be an airborne system that will be deployed in operational environments. Unlike existing technologies, the CTWS will produce a 3D characterization of an instantaneous snapshot of the full volume of turbulence on operationally relevant timeframes without the use of retroreflective targets. This is an unprecedented capability and allows a variety of atmospheric parameters anywhere within the probed volume to be calculated from the index data including among others the atmospheric refractive index structure, the inner scale, the Fried parameter, as well as weather related parameters including wind speed. The CTWS system will be prototyped and flight tested in the Phase II effort.BENEFIT:The United States Air Force currently deploys and anticipates more widespread deployment of a variety of active electro-optical sensors and systems including laser altimeters, wind lidar, free-space optical communications, vibrometry, and coherent imaging sensors including synthetic aperture and holographic ladar imaging. The performance of all of these systems is impacted by atmospheric turbulence. Atmospheric turbulence has been extensively studied both theoretically and experimentally, but remains largely an intractable problem particularly in low altitude slant-path applications due to its inherent randomness, chaotic unpredictability, and strong effects. Typically, turbulence is characterized by the path-integrated structure constant or the Fried parameter, whereas the performance of electro-optic systems depends on the structure constant as a function of distance. Bridger Photonics, Inc. and Montana State University Spectrum Lab propose to develop a system to characterize the atmospheric turbulence as a function of distance but also in a spatially and temporally resolved manner. The success of such an approach would represent a significant leap forward in the characterization of atmospheric turbulence and may unlock a deeper understanding of a fundamentally chaotic problem. In addition, data collected with the sensor will assist the Air Forces need for improved electro-optic, coherent imaging and coherent communications systems.