“…See, e.g., the reviews in [30] and [33]. Many authors have considered generalizations of kriging to functional data: ordinary kriging for functional data is for instance considered in [15,20,34], universal kriging in [9,31,32], kriging with external drift in [24], and cokriging in [21]. Other authors have proposed smoothing methods [1,3,7,29] using roughness penalties that account separately for the regularity of the field in space and in time, in tensor product approaches.…”