“…In geostatistics analysis, such as the Kriging (Kleijnen, 2009), generalized Kriging (Xu & Shu, 2015), Bayesian Maximum Entropy (Yu & Wang, 2013), etc., the spatiotemporal heterogeneous variation is considered where the temporal variation is a function of time distance and the spatial variation is a function of spatial distance, and the covariance function is used to describe the structure of heterogeneity (de Marsily et al, 2005). However, for the spatiotemporal heterogeneity, the construction of spatiotemporal covariance often faces problems, such as the inconsistent dimensions of space and time (or the unity of "distance" units of time and space) (Kleijnen, 2009;Xu & Shu, 2015). Although, some spatiotemporal covariance models, such as the separable model (Graeler et al, 2016), nonseparable model (Ruiz-Medina et al, 2016), and product-sum model (De Iaco et al, 2001), are proposed to try to solve the above problems.…”