of a separate time series for every individual seismic receiver used alternatively some or all of the outputs of the seismic receivers may be combined prior to recording for example each of the seismic receivers of the array may be electrically interconnected and a single time series for the entire array may be recorded the next step 504 may be to modify a directionality function of the virtual source for seismic interferometry this may involve combining at least two of the time series from the seismic receivers included in the array this combining may be performed after the time series have been recorded by for example a computer processor and computer program product this combining may involve performing mathematical operations on the output signals of the seismic receivers of the array prior to combining the outputs and recording a single time series for the array fig6 is a flow chart of an embodiment of a method of modifying a directionality function of a virtual source used in seismic interferometry although the flow chart illustrates the steps in a particular order this is for exemplary purposes only and the order of the steps may be rearranged from that depicted in fig6 the first step 601 illustrated in fig6 is to record seismic wave data incident on each seismic receiver of an array of seismic receivers the virtual source may be associated with the area in which the array of seismic receivers is located the.