IMAGING PRINCIPLE

Migration includes two distinct steps: downward extrapolation in depth or backward extrapolation in time, and imaging for the desired attribute. When the desired attribute is related to the impedance contrasts in the subsurface Claerbout's imaging principle (Claerbout, 1971) represents the basis for many imaging condition equations. According to this principle, a reflector exists at a point where the upcoming and the downgoing wavefields coincide in time and space. There are two distinct aspects behind this principle: the choice of the specific attribute that we seek to image (imaging condition), and the definition of the procedure to be used in the estimation of that attribute (imaging criterion).

If the migration is designed with the sole purpose of obtaining a structural image of the compressional impedance contrasts in the subsurface, then the image condition must be formulated so that it favors noise reduction over amplitude preservation. If however the goal is to obtain an image of attributes that can be correlated to the fluid content of porous rocks, or used as the basic information for a lithological inversion scheme, then the imaging condition must represent a statistically meaningful estimation of that attribute.