Power in the bucket and angle of arrival modelling in the presence of an airborne platform-induced turbulence

In the framework of a European collaborative research project called ALWS (Airborne platform effects on lasers and Warning Sensors), the effects of platform-related turbulence on MAWS (missile approach warning systems) and DIRCM (directed infrared countermeasures) performance are investigated. Field trials have been conducted to study the turbulence effects around a hovering helicopter and behind a turboprop aircraft on the ground, with engines running. The time dependence of the power in the bucket and the amplitude of the angle of arrival have been characterized during the trial. Temporal spectra of these two parameters present an asymptotic behavior typical of optical beams propagating through developed turbulence (Kolmogorov). Based on the formalism developed in the case of propagation through atmospheric turbulence, we have first estimated turbulence strength and wind velocity inside plume for different flight conditions. We have then proposed an approach to simulate times series of these two quantities in the same conditions. These simulated time series have been compared with the recorded data to assess their validity domain. This model will be integrated in a simulator to estimate the impact of the turbulence induced by the platform and calculate the system performance. In this model dedicated to plume and downwash effects, aero-optical effects are not taken into account.