Geostatistical Functional Data Analysis Explore the intersection between geostatistics and functional data analysis with this insightful new reference Geostatistical Functional Data Analysis presents a unified approach to modelling functional data when spatial and spatio-temporal correlations are present. The Editors link together the wide research areas of geostatistics and functional data analysis to provide the reader with a new area called geostatistical functional data analysis that will bring new insights and new open questions to researchers coming from both scientific fields. This book provides a complete and up-to-date account to deal with functional data that is spatially correlated, but also includes the most innovative developments in different open avenues in this field. Containing contributions from leading experts in the field, this practical guide provides readers with the necessary tools to employ and adapt classic statistical techniques to handle spatial regression. The book also includes: A thorough introduction to the spatial kriging methodology when working with functions A detailed exposition of more classical statistical techniques adapted to the functional case and extended to handle spatial correlations Practical discussions of ANOVA, regression, and clustering methods to explore spatial correlation in a collection of curves sampled in a region In-depth explorations of the similarities and differences between spatio-temporal data analysis and functional data analysis Aimed at mathematicians, statisticians, postgraduate students, and researchers involved in the analysis of functional and spatial data, Geostatistical Functional Data Analysis will also prove to be a powerful addition to the libraries of geoscientists, environmental scientists, and economists seeking insightful new knowledge and questions at the interface of geostatistics and functional data analysis.

Table of Contents:
List of Contributors xiii Foreword xvi 1 Introduction to Geostatistical Functional Data Analysis 1 Jorge Mateu and Ramón Giraldo 1.1 Spatial Statistics 1 1.2 Spatial Geostatistics 7 1.2.1 Regionalized Variables 7 1.2.2 Random Functions 7 1.2.3 Stationarity and Intrinsic Hypothesis 9 1.3 Spatiotemporal Geostatistics 12 1.3.1 Relevant Spatiotemporal Concepts 12 1.3.2 Spatiotemporal Kriging 16 1.3.3 Spatiotemporal Covariance Models 17 1.4 Functional Data Analysis in Brief 18 References 22 Part I Mathematical and Statistical Foundations 27 2 Mathematical Foundations of Functional Kriging in Hilbert Spaces and Riemannian Manifolds 29 Alessandra Menafoglio, Davide Pigoli, and Piercesare Secchi 2.1 Introduction 29 2.2 Definitions and Assumptions 30 2.3 Kriging Prediction in Hilbert Space: A Trace Approach 33 2.3.1 Ordinary and Universal Kriging in Hilbert Spaces 33 2.3.2 Estimating the Drift 36 2.3.3 An Example: Trace-Variogram in Sobolev Spaces 37 2.3.4 An Application to Nonstationary Prediction of Temperatures Profiles 39 2.4 An Operatorial Viewpoint to Kriging 42 2.5 Kriging for Manifold-Valued Random Fields 45 2.5.1 Residual Kriging 45 2.5.2 An Application to Positive Definite Matrices 47 2.5.3 Validity of the Local Tangent Space Approximation 49 2.6 Conclusion and Further Research 53 References 53 3 Universal, Residual, and External Drift Functional Kriging 55 Maria Franco-Villoria and Rosaria Ignaccolo 3.1 Introduction 56 3.2 Universal Kriging for Functional Data (UKFD) 56 3.3 Residual Kriging for Functional Data (ResKFD) 58 3.4 Functional Kriging with External Drift (FKED) 60 3.5 Accounting for Spatial Dependence in Drift Estimation 61 3.5.1 Drift Selection 62 3.6 Uncertainty Evaluation 62 3.7 Implementation Details in R 64 3.7.1 Example: Air Pollution Data 64 3.8 Conclusions 69 References 71 4 Extending Functional Kriging When Data Are Multivariate Curves: Some Technical Considerations and Operational Solutions 73 David Nerini, Claude Manté, and Pascal Monestiez 4.1 Introduction 73 4.2 Principal Component Analysis for Curves 74 4.2.1 Karhunen–Loève Decomposition 74 4.2.2 Dealing with a Sample 76 4.3 Functional Kriging in a Nutshell 78 4.3.1 Solution Based on Basis Functions 79 4.3.2 Estimation of Spatial Covariances 81 4.4 An Example with the Precipitation Observations 82 4.4.1 Fitting Variogram Model 83 4.4.2 Making Prediction 83 4.5 Functional Principal Component Kriging 85 4.6 Multivariate Kriging with Functional Data 88 4.6.1 Multivariate FPCA 91 4.6.2 MFPCA Displays 93 4.6.3 Multivariate Functional Principal Component Kriging 94 4.6.4 Mixing Temperature and Precipitation Curves 96 4.7 Discussion 98 4.A Appendices 100 4.A.1 Computation of the Kriging Variance 100 References 102 5 Geostatistical Analysis in Bayes Spaces: Probability Densities and Compositional Data 104 Alessandra Menafoglio, Piercesare Secchi, and Alberto Guadagnini 5.1 Introduction and Motivations 104 5.2 Bayes Hilbert Spaces: Natural Spaces for Functional Compositions 105 5.3 A Motivating Case Study: Particle-Size Data in Heterogeneous Aquifers –Data Description 108 5.4 Kriging Stationary Functional Compositions 110 5.4.1 Model Description 110 5.4.2 Data Preprocessing 112 5.4.3 An Example of Application 113 5.4.4 Uncertainty Assessment 116 5.5 Analyzing Nonstationary Fields of FCs 119 5.6 Conclusions and Perspectives 123 References 124 6 Spatial Functional Data Analysis for Probability Density Functions: Compositional Functional Data vs. Distributional Data Approach 128 Elvira Romano, Antonio Irpino, and Jorge Mateu 6.1 FDA and SDA When Data Are Densities 130 6.1.1 Features of Density Functions as Compositional Functional Data 131 6.1.2 Features of Density Functions as Distributional Data 135 6.2 Measures of Spatial Association for Georeferenced Density Functions 138 6.2.1 Identification of Spatial Clusters by Spatial Association Measures for Density Functions 139 6.3 Real Data Analysis 141 6.3.1 The SDA Distributional Approach 143 6.3.2 The Compositional–Functional Approach 145 6.3.3 Discussion 147 6.4 Conclusion 149 Acknowledgments 151 References 151 Part II Statistical Techniques for Spatially Correlated Functional Data 155 7 Clustering Spatial Functional Data 157 Vincent Vandewalle, Cristian Preda, and Sophie Dabo-Niang 7.1 Introduction 157 7.2 Model-Based Clustering for Spatial Functional Data 158 7.2.1 The Expectation–Maximization (EM) Algorithm 160 7.2.1.1 E Step 161 7.2.1.2 M Step 161 7.2.2 Model Selection 161 7.3 Descendant Hierarchical Classification (HC) Based on Centrality Methods 162 7.3.1 Methodology 164 7.4 Application 165 7.4.1 Model-Based Clustering 167 7.4.2 Hierarchical Classification 169 7.5 Conclusion 171 References 172 8 Nonparametric Statistical Analysis of Spatially Distributed Functional Data 175 Sophie Dabo-Niang, Camille Ternynck, Baba Thiam, and Anne-Françoise Yao 8.1 Introduction 175 8.2 Large Sample Properties 178 8.2.1 Uniform Almost Complete Convergence 180 8.3 Prediction 181 8.4 Numerical Results 184 8.4.1 Bandwidth Selection Procedure 184 8.4.2 Simulation Study 185 8.5 Conclusion 193 8.A Appendix 194 8.A.1 Some Preliminary Results for the Proofs 194 8.A.2 Proofs 196 8.A.2.1 Proof of Theorem 8.1 196 8.A.2.2 Proof of Lemma A.3 196 8.A.2.3 Proof of Lemma A.4 196 8.A.2.4 Proof of Lemma A.5 201 8.A.2.5 Proof of Lemma A.6 201 8.A.2.6 Proof of Theorem 8.2 202 References 207 9 A Nonparametric Algorithm for Spatially Dependent Functional Data: Bagging Voronoi for Clustering, Dimensional Reduction, and Regression 211 Valeria Vitelli, Federica Passamonti, Simone Vantini, and Piercesare Secchi 9.1 Introduction 211 9.2 The Motivating Application 212 9.2.1 Data Preprocessing 214 9.3 The Bagging Voronoi Strategy 216 9.4 Bagging Voronoi Clustering (BVClu) 218 9.4.1 BVClu of the Telecom Data 221 9.4.1.1 Setting the BVClu Parameters 221 9.4.1.2 Results 223 9.5 Bagging Voronoi Dimensional Reduction (BVDim) 223 9.5.1 BVDim of the Telecom Data 225 9.5.1.1 Setting the BVDim Parameters 225 9.5.1.2 Results 227 9.6 Bagging Voronoi Regression (BVReg) 231 9.6.1 Covariate Information: The DUSAF Data 232 9.6.2 BVReg of the Telecom Data 234 9.6.2.1 Setting the BVReg Parameters 234 9.6.2.2 Results 235 9.7 Conclusions and Discussion 236 References 239 10 Nonparametric Inference for Spatiotemporal Data Based on Local Null Hypothesis Testing for Functional Data 242 Alessia Pini and Simone Vantini 10.1 Introduction 242 10.2 Methodology 244 10.2.1 Comparing Means of Two Functional Populations 244 10.2.2 Extensions 248 10.2.2.1 Multiway FANOVA 249 10.3 Data Analysis 250 10.4 Conclusion and FutureWorks 256 References 258 11 Modeling Spatially Dependent Functional Data by Spatial Regression with Differential Regularization 260 Mara S. Bernardi and Laura M. Sangalli 11.1 Introduction 260 11.2 Spatial Regression with Differential Regularization for Geostatistical Functional Data 264 11.2.1 A Separable Spatiotemporal Basis System 265 11.2.2 Discretization of the Penalized Sum-of-Square Error Functional 268 11.2.3 Properties of the Estimators 271 11.2.4 Model Without Covariates 273 11.2.5 An Alternative Formulation of the Model 274 11.3 Simulation Studies 274 11.4 An Illustrative Example: Study of the Waste Production in Venice Province 278 11.4.1 The Venice Waste Dataset 278 11.4.2 Analysis of Venice Waste Data by Spatial Regression with Differential Regularization 279 11.5 Model Extensions 282 References 283 12 Quasi-maximum Likelihood Estimators for Functional Linear Spatial Autoregressive Models 286 Mohamed-Salem Ahmed, Laurence Broze, Sophie Dabo-Niang, and Zied Gharbi 12.1 Introduction 286 12.2 Model 288 12.2.1 Truncated Conditional Likelihood Method 291 12.3 Results and Assumptions 293 12.4 Numerical Experiments 298 12.4.1 Monte Carlo Simulations 298 12.4.2 Real Data Application 305 12.5 Conclusion 312 12.A Appendix 313 Proof of Proposition 12.A.1 313 Proof of Theorem 12.1 314 Proof of Theorem 12.2 317 Proof of Theorem 12.3 319 Proof of Lemma 12.A.2 322 Proof of Lemma 12.A.3 322 Proof of Lemma 12.A.5 323 References 325 13 Spatial Prediction and Optimal Sampling for Multivariate Functional Random Fields 329 Martha Bohorquez, Ramón Giraldo, and Jorge Mateu 13.1 Background 329 13.1.1 Multivariate Spatial Functional Random Fields 329 13.1.2 Functional Principal Components 330 13.1.3 The Spatial Random Field of Scores 331 13.2 Functional Kriging 332 13.2.1 Ordinary Functional Kriging (OFK) 332 13.2.2 Functional Kriging Using Scalar Simple Kriging of the Scores (FKSK) 333 13.2.3 Functional Kriging Using Scalar Simple Cokriging of the Scores (FKCK) 333 13.3 Functional Cokriging 336 13.3.1 Cokriging with Two Functional Random Fields 336 13.3.2 Cokriging with P Functional Random Fields 338 13.4 Optimal Sampling Designs for Spatial Prediction of Functional Data 340 13.4.1 Optimal Spatial Sampling for OFK 341 13.4.2 Optimal Spatial Sampling for FKSK 341 13.4.3 Optimal Spatial Sampling for FKCK 342 13.4.4 Optimal Spatial Sampling for Functional Cokriging 343 13.5 Real Data Analysis 344 13.6 Discussion and Conclusions 348 References 348 Part III Spatio–Temporal Functional Data 351 14 Spatio–temporal Functional Data Analysis 353 Gregory Bopp, John Ensley, Piotr Kokoszka, and Matthew Reimherr 14.1 Introduction 353 14.2 Randomness Test 355 14.3 Change-Point Test 359 14.4 Separability Tests 362 14.5 Trend Tests 365 14.6 Spatio–Temporal Extremes 369 References 373 15 A Comparison of Spatiotemporal and Functional Kriging Approaches 375 Johan Strandberg, Sara Sjöstedt de Luna, and Jorge Mateu 15.1 Introduction 375 15.2 Preliminaries 376 15.3 Kriging 378 15.3.1 Functional Kriging 378 15.3.1.1 Ordinary Kriging for Functional Data 378 15.3.1.2 Pointwise Functional Kriging 380 15.3.1.3 Functional Kriging Total Model 381 15.3.2 Spatiotemporal Kriging 382 15.3.3 Evaluation of Kriging Methods 384 15.4 A Simulation Study 385 15.4.1 Separable 385 15.4.2 Non-separable 390 15.4.3 Nonstationary 391 15.5 Application: Spatial Prediction of Temperature Curves in the Maritime Provinces of Canada 394 15.6 Concluding Remarks 400 References 400 16 From Spatiotemporal Smoothing to Functional Spatial Regression: a Penalized Approach 403 Maria Durban, Dae-Jin Lee, María del Carmen Aguilera Morillo, and Ana M. Aguilera 16.1 Introduction 403 16.2 Smoothing Spatial Data via Penalized Regression 404 16.3 Penalized Smooth Mixed Models 407 16.4 P-spline Smooth ANOVA Models for Spatial and Spatiotemporal data 409 16.4.1 Simulation Study 411 16.5 P-spline Functional Spatial Regression 413 16.6 Application to Air Pollution Data 415 16.6.1 Spatiotemporal Smoothing 416 16.6.2 Spatial Functional Regression 416 Acknowledgments 421 References 421 Index 424