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- W1888049773 abstract "The hot exhaust gases from engines on helicopters are pushed down by the rotor in a turbulent flow. When the opticalpath of a laser beam or optical sensor passes through this region severe aberrations of the optical field may result. Theseperturbations will lead to beam wander and beam distortions that can limit the performance of optical countermeasuresystems.To quantify these effects the Italian Air Force Flight Test Centre hosted a trial for the “Airborne platform effects onlasers and warning sensors” (ALWS) EDA-project. Laser beams were propagated from the airport control tower to atarget screen in a slant path with the helicopter hovering over this path. Collimated laser beams at 1.55-, 2- and 4.6-μmwavelength were imaged with high speed cameras. Large increases in beam wander and beam divergence were found,with beam wander up to 200 μrad root-mean-square and increases in beam divergence up to 1 mrad.To allow scaling to other laser beam parameters and geometries formulas for propagation in atmospheric turbulence wereused even though the turbulence may not follow Kolmogorov statistics. By assuming that the plume is short compared tothe total propagation distance the integrated structure parameter through the plume could be calculated. Values in therange 10 -10 to 10 -8 m 1/3 were found when the laser beams passed through the exhaust gases below the helicopter tail. Theintegrated structure parameter values calculated from beam wander were consistently lower than those calculated fromlong term spot size, indicating that the method is not perfect but provides information about order of magnitudes.The measured results show that the engine exhaust for worst case beam directions will dominate over atmosphericturbulence even for kilometer path lengths from a helicopter at low altitude. How severe the effect is on systemperformance will depend on beam and target parameters." @default.
- W1888049773 created "2016-06-24" @default.
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- W1888049773 date "2015-10-27" @default.
- W1888049773 modified "2023-10-18" @default.
- W1888049773 title "Helicopter engine exhaust rotor downwash effects on laser beams" @default.
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- W1888049773 doi "https://doi.org/10.1117/12.2194815" @default.
- W1888049773 hasPublicationYear "2015" @default.
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