9.25 Let Wt , t Z2, be a WN(0, 2) spatial series and u = v.

9.25 Let Wt , t ∈ Z2, be a WN(0, σ2) spatial series and u = v. Show that (9.68) is bounded a.s. if and only if

γˆ (u, v) − γ (u, v) = O

-

log log |n|

|n|



a.s., where γ (u, v) and γˆ (u, v) are the ACV and sample ACV of Wt at u and v, respectively.