Since the 1970s a main topic in vortex research is the problem of wake vortex hazard. This thesis focuses on the aspect of engine jet vortex interaction and discusses experimental results from low speed wind tunnel tests in the wake of a swept wing half model with a model engine that can be span wise moved during wind tunnel operation.The falsifying effect of vortex meandering or unsteady movement on the evaluation of wake vortex measurements using PIV technique is analysed by a numerical method. For different distributions of vortex centre positions, amplitudes of wandering motion, vortex models and PIV dependent parameters the original vortex profiles are compared with the result of an ensemble averaging process over different numbers of data sets. Depending on the vortex model and the extent of vortex movement for the averaging process concerning characteristic vortex parameters like the maximum tangential velocity or the peak vorticity errors up to over 20% resp. over 40% can be predicted for the observed measurement range.The experimental data therefore are evaluated with a new averaging method that accounts for the unsteady vortex centre positions and significantly enhances the dynamic range of the measurement signal, by a factor of five and more. The results of this centred averaging method are compared to the prediction from the numerical method.