A technique includes receiving seismic data acquired in a seismic survey. The survey has an associated undersampled direction, and the seismic data contains samples, which are indicative of a pressure wavefield and a directional derivative of the pressure wavefield that contains information related to vertical variations. The technique includes relating the samples to the pressure wavefield or to the directional derivative of the pressure wavefield using at least one linear filter and based on the relationship, constructing a substantially unaliased continuous representation of the pressure wavefield or the directional derivative of the pressure wavefield along the undersampled direction.