1. Amanda S. Hering is Assistant Professor, Department of Mathematical and Computer Sciences, Colorado School of Mines, Golden, CO 80401-1887 . Marc G. Genton is Professor, Department of Statistics, Texas A&M University, College Station, TX 77843-3143 . This research was partially supported by NSF grants DMS-0504896, CMG ATM-0620624, and Award No. KUS-C1-016-04, made by King Abdullah University of Science and Technology (KAUST). The authors would like to thank the Editor and two referees for their helpful...