1. A method of processing seismic data corresponding to first arrival waves and to waves reflected or converted by the seismic horizons, the seismic data being acquired by an omnitilt sensor having at least three geophone components with an angular orientation φψ, wherein estimators are determined which are combinations of these components, wherein various data are isolated, through the estimators, depending on whether they correspond to propagation with reflection or with conversion by the seismic horizons, and wherein operators to be applied to the various components of the sensor are determined for determining a sensor reconstruction, the operators being those that minimize a deviation between reference data and data obtained by applying the estimators to the sensor reconstruction, the operators thus determined being applied to the data acquired, said operators used to reconstruct the orientation of at least one geophone of the omnitilt sensor along at least one desired axis.