To attack the coexistence of the reflection wave field and the direct waves in the correlation space of a passive seismic data set, I propose two methods to attempt their separation. One is from a standpoint of the data consisting of signal and noise components. The other is by extracting up-going and down-going components from the recorded wave field if we have three-component receivers. Both methodologies will be pursued in an effort to fully understand minimum design parameters for a successful passive seismic imaging experiment.