OUR OBJECTIVES ARE TO (1) INVESTIGATE THE IMPACT OF NEGLECTED INTER-SITE CORRELATIONS AND TO ANALYZE DIFFERENT METHODS FOR ACCOUNTING FOR THE IMPACT OF THEM IN DERIVING SPATIALLY AVERAGED PARAMETERS FROM REGIONS WITH PPP PROCESSING RESULTS AND (2) SINCE INTER-SITE CORRELATIONS ARE ACCESSIBLE WHEN NETWORK PROCESSING IS USED TO DEVELOP ALGORITHMS AND SCRIPTS THAT CAN BE IMPLEMENTED BY USERS OF THE MIT GAMIT/GLOBK GNSS ANALYSIS SOFTWARE WHO WANT TO PERFORM LARGE GNSS NETWORK PROCESSING. TO ADDRESS THESE OBJECTIVES WE WILL CARRY OUT EXTENSIVE GNSS DATA PROCESSING AND THESE RESULTS WILL BE MADE AVAILABLE THROUGH THE IGS PRODUCT SERVICES WHERE APPROPRIATE AND OUR OWN FTP/HTTP SERVER. WE WILL ALSO INVESTIGATE SPECIFIC CASES OF TRANSIENT MOTIONS WITH LARGE SPATIAL EXTENT AS A MEANS TO ASSESS THE IMPACT OF INTER-SITE CORRELATIONS AND DETERMINE THE EFFECTIVENESS OF THE APPROACHES WE DEVELOP TO ACCOUNT FOR THEM. OUR RESEARCH WILL DIRECTLY ADDRESS FOUR OF CHALLENGES POSED IN THE NASA CHALLENGES AND OPPORTUNITIES FOR RESEARCH IN ESI (CORE) REPORT (2016) (HTTP://GO.NASA.GOV/2GFMLAQ). OUR EXPLORATION OF THE IMPACT OF INTER SITE CORRELATIONS WILL EXAMINE SPECIFIC CASES AND CLASSES OF PROBLEMS THAT WILL ADDRESS CHALLENGES: 2.1 "WHAT IS THE NATURE OF DEFORMATION ASSOCIATED WITH PLATE BOUNDARIES." ; 2.2 "HOW DO TECTONIC PROCESSES AND CLIMATE VARIABILITY INTERACT TO SHAPE EARTH'S SURFACE AND CREATE NATURAL HAZARDS?"; 2.3 "HOW DOES THE SOLID EARTH RESPOND TO CLIMATE-DRIVEN EXCHANGE OF WATER AMONG EARTH SYSTEMS.." AND 2.7 "HOW DO HUMAN ACTIVITIES IMPACT AND INTERACT WITH EARTH'S SURFACE AND INTERIOR?". THE IMPACT OF OUR RESEARCH WILL BE IN ASSESSING THE ERROR BUDGETS AND SIGNIFICANCE LEVELS ASSOCIATED WITH INFERENCES ABOUT THE CHALLENGES GIVEN ABOVE. OUR GENERAL APPROACH WILL BE TWOFOLD: (1) USE OF FULL VARIANCE-COVARIANCE MATRICES TO CAPTURE THE IMPACT OF INTER-SITE CORRELATIONS BOTH FROM GNSS DATA NOISE AND FROM (MOST LIKELY MORE IMPORTANTLY) MODEL DEFICIENCY "NOISE"; AND (2) EMPIRICAL MODELING OF THE CORRELATIONS AND COVARIANCES THROUGH SPATIAL INTERPOLATION METHODS AND ENSEMBLE AVERAGING. BOTH OF THESE APPROACHES WILL BE USED TO ADDRESS ISSUES ASSOCIATED WITH TEMPORAL VARIATIONS OF GLOBAL AND REGIONAL HEIGHT VARIATIONS AND IN EXPLORING TRANSIENT MOTIONS IN GNSS STATION POSITONS.