Investigating motion blur and temporal aliasing from time-lapse electrical resistivity

Abstract

Geophysical monitoring through time-lapsed resistivity imaging is investigated to determine detrimental effects resulting from temporal smear. Temporal smear can be divided into motion blur and temporal aliasing, with motion blur attributed to an extended sample integration time relative to the velocity of a moving target, thus giving rise to reproduced targets that are distorted versions of the real target shape. Aliasing results from undersampling across time and may give a discontinuous movement. The degree to which each aspect of smear affects target properties described by spatial moment analysis depends on the spatial resolution of the imaging method and the degree to which temporal degradation is applied. For synthetic models with relatively high spatial resolution, aliasing effects were slight except in cases where the minimal number of snapshots was acquired to understand the end state condition of the target. Motion blur, on the other hand, had progressive detrimental effects with each level of additional smearing. For field data acquired during subsurface injection with a lower resolution array, the damaging effects from motion blur and temporal aliasing were equivalent. Both aspects showed progressive degeneration of spatial moments with each level of degradation. To combat this problem in the short term, it is recommended to acquire resistivity data as rapidly as possible and sacrifice some spatial resolution to enhance temporal resolution. In the future, there may be methods adopted from motion photography to deblur target motion by using the point spread function. Aliasing, however, can only be solved through continuous sampling.