Seismic interferometry gives rise to a correlation wavefield that is closely related to the Green’s function under the condition of uniformly distributed noise sources. In the presence of an additional isolated noise source, a second contribution to this wavefield is introduced that emerges from the isolated source location at negative lapse time. These two contributions interfere, which may bias surface wave dispersion measurements significantly. To avoid bias, the causal and acausal parts of correlation functions need to be treated separately. We illustrate this by applying seismic interferometry to field data from a large-N array where a wind farm is present within the array