(ap’ ∂ ch∂r,) 1. An opening, gate, or window that limits the information affecting a measuring device. (The seismic spread length can be considered the aperture of a seismic system.) 2. In processing, the spatial range of the data considered in a calculation (e.g., the range of data considered in seismic migration) or the time range of the data considered (e.g., in deconvolution). Values near the edges of an aperture are often tapered rather than abrupt. The effective aperture width is the width of a boxcar with the same peak height and area. 3. The additional extent of a survey required to correctly image data in the required image area.