Different methods have been proposed to apply weights according to different criteria. For example, the smart stacking proposed by Rashed (2008) is based on sign difference between sample point and the alpha-trimmed mean to remove frequency distortions. Neelamani et al. (2006) uses an iterative algorithm called leave me out (LMO) to estimate noise variances from data. The desired signal is assumed to be flat with constant amplitude across all the traces within a gather in the LMO method.