Covariance Function

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  • a new Covariance Function and spatio temporal prediction kriging for a stationary spatio temporal random process
    Journal of Time Series Analysis, 2017
    Co-Authors: Subba T Rao, Gyorgy Terdik
    Abstract:

    Consider a stationary spatio-temporal random process Yts;s∈Rd,t∈Z and let Ytsi;i=1,2,…,m;t=1,…,n be a sample from the process. Our object here is to predict, given the sample, Ytso for all t at the location so. To obtain the predictors, we define a sequence of discrete Fourier transforms Jsiωj;i=1,2,…,m using the observed time series. We consider these discrete Fourier transforms as a sample from the complex valued random variable Jsω. Assuming that the discrete Fourier transforms satisfy a complex stochastic partial differential equation of the Laplacian type with a scaling Function that is a polynomial in the temporal spectral frequency ω, we obtain, in a closed form, expressions for the second-order spatio-temporal spectrum and the Covariance Function. The spectral density Function obtained corresponds to a non-separable random process. The optimal predictor of the discrete Fourier transform Jsoω is in terms of the Covariance Functions. The estimation of the parameters of the spatio-temporal Covariance Function is considered and is based on the recently introduced frequency variogram method. The methods given here can be extended to situations where the observations are corrupted by independent white noise. The methods are illustrated with a real data set.