Some inversion schemes amount to little more than a relative impedance (from the seismic) added to a low frequency model. This can be easily demonstrated by filtering the low frequency out of the inversion result and comparing with relative impedance.

An example is shown in Figure 2. A commercial sparse spike inversion algorithm has been used to compute absolute elastic impedance (Figure 2a). By applying a low pass filter, the low frequency model is obtained (Figure 2b). Similarly, a high pass filter reveals the inversion contribution (Figure 2c) which should be compared to the relative elastic impedance obtained by zero phasing and then integrating the seismic traces (Figure 2d). Apart from a slight smoothing effect the sparse spike inversion result is almost indistinguishable from the relative impedance.