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Proceedings Paper

Airborne platform effects on lasers and warning sensors
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Paper Abstract

Airborne platform effects on lasers and warning sensors (ALWS) has been a European collaborative research project to investigate the effects of platform-related turbulence on optical countermeasure systems, especially missile approach warning systems (MAWS) and directed infrared countermeasures (DIRCM). Field trials have been carried out to study the turbulence effects around a hovering helicopter and behind a turboprop aircraft with engines running on the ground. In addition different methods for modelling the effects have been investigated.

In the helicopter trials significant beam wander, scintillations and beam broadening were experienced by narrow divergence laser beams when passing through the down-wash of the hot engine exhaust gases. The measured effects considerably exceed the effects of atmospheric turbulence. Extraction of turbulence parameters for modelling of DIRCM-relevant scenarios show that in most cases the reduction of jamming power and distortion of jamming waveform can be expected to be small. The reduction of effects of turbulence is mainly related to the larger beam divergence and shorter Rayleigh length of DIRCM lasers compared to the experimental probe beams. Measurements using the turboprop platform confirm that tolerable effects on laser beam properties are found when the laser beam passes through the exhaust 15 m behind the outlet where the exhaust gases are starting to cool down.

Modelling efforts have shown that time-resolved computational fluid dynamics (CFD) calculations can be used to study properties of beam propagation in engine exhaust-related turbulence. Because of computational cost and the problem of validating the CFD results the use for system performance simulations is however difficult.

The hot exhaust gases emitted from aircraft engines create extreme optical turbulence in a local region. The effects on countermeasure system performance depend both on the system parameters and on the threat characteristics. With present-day DIRCM systems, the effects of even severe turbulence are often tolerable.

Paper Details

Date Published: 5 October 2017
PDF: 12 pages
Proc. SPIE 10435, Technologies for Optical Countermeasures XIV, 104350M (5 October 2017); doi: 10.1117/12.2277311
Show Author Affiliations
Markus Henriksson, FOI-Swedish Defence Research Agency (Sweden)
Christian Eisele, Fraunhofer-Institut für Optronik, Systemtechnik und Bildauswertung (Germany)
Dirk Seiffer, Fraunhofer-Institut für Optronik, Systemtechnik und Bildauswertung (Germany)
Lars Sjöqvist, FOI-Swedish Defence Research Agency (Sweden)
Fabio Togna, Aeronautica Militare Italiana (Italy)
Marie-Thérèse Velluet, ONERA, The French Aerospace Lab. (France)

Published in SPIE Proceedings Vol. 10435:
Technologies for Optical Countermeasures XIV
David H. Titterton; Robert J. Grasso; Mark A. Richardson, Editor(s)

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