1. A method of wavefield separation comprising: computing a matching operator between pressure sensor and particle motion sensor responses of co-located pressure and particle motion sensors based on pressure and particle motion wavefield measured by the co-located pressure and particle motion sensors and depths of the co-located pressure and particle motion sensors; and computing at least one of up-going pressure wavefield and up-going particle motion wavefield based on the matching operator and the measured pressure and particle motion wavefields.