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Quantification of helicopter rotor downwash effects on electro-optical defensive AIDS suites

: Seiffer, Dirk; Eisele, Christian; Henriksson, Markus; Sjöqvist, Lars; Möller, Sebastian; Togna, F.; Velluet, M.-T.


Ackermann, H. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Technologies for optical countermeasures XII and High power lasers 2015 : Technology and systems; 21, 23 - 24 September 2015, Toulouse, France
Bellingham, WA: SPIE, 2015 (Proceedings of SPIE 9650)
ISBN: 978-1-62841-860-6
Paper 96500I, 10 pp.
Conference "Technologies for Optical Countermeasures" <12, 2015, Toulouse>
Conference "High Power Lasers - Technology and Systems" <2015, Toulouse>
Conference Paper
Fraunhofer IOSB ()
missile warner; DIRCM; rotor downwash; helicopter; ALWS

The performance of electro-optical platform protection systems can be degraded significantly by the propagation environment around the platform. This includes aero-optical effects and zones of severe turbulence generated by engine exhausts. For helicopters rotor tip vortices and engine exhaust gases that are pressed down by the rotor airflow form the so called downwash phenomena. The downwash is a source for perturbations. A wide range of spatial and temporal fluctuations in the refractive index of air can occur. The perturbations from the turbulent flow cause detrimental effects on energy delivery, angle of arrival fluctuations, jam-code transmission, tracking accuracy and imaging performance in general. Therefore the effects may especially have a severe impact on the performance of laser-based protection systems like directed infrared countermeasures (DIRCM). The chain from passive missile detection and warning to obtaining an optical break-lock by the use of an active laser system will be influenced. To anticipate the installed performance of an electro-optical defensive aids suite (DAS) for helicopter platforms it is necessary to develop models for the prediction of the perturbations. Modelled results have to be validated against experimental findings. However, the data available in open literature on the effects of rotor downwash from helicopters on optical propagation is very limited. To collect necessary data and to obtain a first impression about the magnitude of occurring effects the European defence agency group (EDA) on "airborne platform effects on lasers and warning sensors (ALWS)" decided to design and perform a field trial on the premises of the Italian Air Force Flight Test Center in Pratica di Mare, Italy. ALWS is a technical arrangement under the Europa MoU among France, Germany, Italy, Sweden and the United Kingdom.