Abstract
SUMMARY A recently published waveform inversion method is used to extract S-wave velocity from a few waveforms recorded in soft formations. A novel feature of the method is that it does not require estimates of the source and receiver transfer functions. This feature is useful for borehole problems as the sourcereceiver transfer functions may be different for different source-receiver pairs, and vary with depth due to changes of coupling with depth in the hole. actural values. Although Cheng’s spectral ratio eliminates the effects of the unknown source spectrum, it requires accurate estimates of the two receiver transfer functions. Recently Frazer & Sun (1998) presented waveform inversion techniques that are blind to the source wavelet and receiver transfer function. Their fourwise technique is developed here with reference to the LSS data. The LSS tool has two sources and two receivers (Fig 1), so at each depth only four full waveforms are recorded. THEORY
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