A computer-implemented method of de-aliasing seismic data, the method comprising: (a) obtaining a first trace of seismic data representing the propagation of seismic energy through a geological volume of interest from a source positioned at a single source location to detectors positioned at detector locations spaced apart according to a detector spacing, the first trace of seismic data further representing a plurality of detector beam arrivals as a function of time; (b) determining a midpoint dip corresponding to at least one detector beam arrival represented in the first trace of seismic data, wherein the midpoint dip is determined based on arrival time of the at least one detector beam arrival; (c) determining a filter to be applied to the trace of seismic data to remove frequencies of seismic energy from the first trace of seismic data that have been aliased by the detector spacing, the filter being determined based on the midpoint dip corresponding to the at least one beam arrival and the detector spacing; and (d) applying the filter to the first trace of seismic data to remove frequencies of seismic energy from the first trace of seismic data that have been aliased by the detector spacing, characterised in that the detector beams of seismic energy represented in the seismic data have been generated by reflections of source beams of seismic energy emitted from the source such that a given detector beam has been generated by a corresponding source beam having some source dip at the source location, and in that the midpoint dip corresponding to the given detector beam arrival is the sum of a detector dip of the given detector beam arrival and the source dip of the source beam corresponding to the given detector beam arrival. (a) obtaining a first trace of seismic data representing the propagation of seismic energy through a geological volume of interest from a source positioned at a single source location to detectors positioned at detector locations spaced apart according to a detector spacing, the first trace of seismic data further representing a plurality of detector beam arrivals as a function of time; (b) determining a midpoint dip corresponding to at least one detector beam arrival represented in the first trace of seismic data, wherein the midpoint dip is determined based on arrival time of the at least one detector beam arrival; (c) determining a filter to be applied to the trace of seismic data to remove frequencies of seismic energy from the first trace of seismic data that have been aliased by the detector spacing, the filter being determined based on the midpoint dip corresponding to the at least one beam arrival and the detector spacing; and (d) applying the filter to the first trace of seismic data to remove frequencies of seismic energy from the first trace of seismic data that have been aliased by the detector spacing, characterised in that the detector beams of seismic energy represented in the seismic data have been generated by reflections of source beams of seismic energy emitted from the source such that a given detector beam has been generated by a corresponding source beam having some source dip at the source location, and in that the midpoint dip corresponding to the given detector beam arrival is the sum of a detector dip of the given detector beam arrival and the source dip of the source beam corresponding to the given detector beam arrival.