A method of processing seismic data acquired consequent to actuation of a seismic source is described. The method comprises taking the result of the following process into account when processing the seismic data where the process comprises estimating the effect of uncertainty in the position and/or orientation of the seismic source relative to the measuring receiver on processing the seismic data by estimating a source wavefield from data acquired by a near-field measuring receiver and from a first parameter set including at least one parameter indicative of the position and/or orientation of the seismic source relative to the measuring receiver, varying the value of at least one parameter of the first parameter set, estimating the source wavefield from the data acquired by the measuring receiver and from the varied first parameter set and obtaining information about the uncertainty in the estimate of the source wavefield.