Dictionary:Downward continuation

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{{#category_index:D|downward continuation}} 1. Determining the value of a potential (e.g., gravitational) field at a lower elevation from values measured at a higher elevation, based on the field continuity. A potential field is not continuous across the boundaries of anomalous masses. As the depth from which an anomaly originates is approached, its expression becomes sharper and tends to outline the mass better until its depth is reached; beyond this point the field computed by continuation becomes erratic. Noise data often precludes successful application. Sometimes used in depth estimation. See continuation. 2. Calculating over a surface at depth the values of any quantity that can be determined from shallower measurements. Often refers to calculating the seismic wavefield at depth, as is done in finite-difference migration.