f Behaviour of prestack backus filters for multiple suppression

Among prestack methods tor peg-leg elimination, one powerful technique consists in subtracting from the initial data a multiple model obtained by wave equation propagation of the CMP gathers through the water layer . This method is very useful when the differential moveout between the primaries and the multiple events is not significant enough (or separation using bidimensional filters, or when the multiples are a-periodic . The subtraction approach consists of parametrical adaptation of the multiple model based on least-squares (or least absolute valnes) optimization . Nevertheless, the efficiency of the subtraction may be attenuated by circumstances such as a low signal-to-noise ratio . On the other hand, it the parametrization of the adaptation is not sulficientty constrained, the primary reflections may be damaged. In the case of strong sea bottom reflection coefficients, the amplitude variations between the different orders of the reverberations (according to Backus (1959)), cannot be fitted using one single multiple model, without strongly relaxing the time variability of the parameters allowing the adaptation .