  We develop an optimized technique to extract density--density and
velocity--velocity spectra out of observed spectra in redshift space. The
measured spectra of the distribution of halos from redshift distorted mock map
are binned into 2--dimensional coordinates in Fourier space so as to be
decomposed into both spectra using angular projection dependence. With the
threshold limit introduced to minimize nonlinear suppression, the decomposed
velocity--velocity spectra are reasonably well measured up to scale k=0.07
h/Mpc, and the measured variances using our method are consistent with errors
predicted from a Fisher matrix analysis. The detectability is extendable to
k\sim 0.1 h/Mpc with more conservative bounds at the cost of weakened
constraint.
