Abstract
A great number of GPS stations have been installed in the Houston, Texas area for studying ground deformation caused by subsidence, salt dome uplift, and fault creep. One major consideration in determining the magnitude and velocity of ground displacement over time using GPS, particularly for horizontal ground deformations, is the selection of reference frames. In this study, we define a Stable Houston Reference Frame (SHRF) using over 8-year of continuous data from 10 permanent GPS stations. These stations are located throughout Harries County and nearby counties, and cover an area of about 200,000 km 2 . The realization of SHRF is defined in terms of a Helmert transformation from the International GNSS (Global Navigation Satellite System) Reference Frame of 2008 (IGS08). SHRF is aligned with the IGS08 at epoch 2012.0. The velocities of these 10 frame stations are minimized to zero within the stable reference frame. The GIPSY/OASIS (V6.1.2) software package was used to calculate position coordinates within IGS08. The precise point positioning (PPP) daily solutions within SHRF achieve 2-3 mm horizontal accuracy and 6-7 mm vertical accuracy. The main results of this article include (1) accurate global (IGS08) positions and velocities of 10 selected frame sites, and (2) 14 parameters for reference frame transformation from IGS08 to SHRF. SHRF will be incrementally improved and be synchronized with the update of IGS reference frame.
Highlights
The Houston metropolitan area of Texas, as described in this article, includes all of Harris County and Galveston County, and parts of surrounding counties, Brazoria, Fort Bend, Waller, Montgomery, Liberty, and Chambers Counties
A great number of GPS stations have been installed in the Houston, Texas area for studying ground deformation caused by subsidence, salt dome uplift, and fault creep
Final satellite orbits and clocks provided by the International GNSS (Global Navigation Satellite System) Service (IGS) (Dow et al, 2009) and wide lane and phase bias estimates provided by the Jet Propulsion Laboratory (JPL) (Bertiger et al, 2010) were used in precise point positioning (PPP) processing
Summary
The Houston metropolitan area of Texas, as described in this article, includes all of Harris County and Galveston County, and parts of surrounding counties, Brazoria, Fort Bend, Waller, Montgomery, Liberty, and Chambers Counties. In addition to the PAM GPS network, there are currently more than twenty Continuously Operating Reference Stations (CORS) in the Houston area (Wang and Soler, 2013) These CORS sites are operated by the Texas Department of Transportation, the City of Houston, and other local agencies. National Science Foundation (NSF) awarded the University of Houston with a research project (2012–2015) to establish a realtime GPS network with 40 permanent stations in the Houston area for the study of multiple urban natural hazards, including subsidence, faulting, salt dome uplift, flooding, and hurricane intensity forecasts. Houston experiences ground instability problems in several ways, from subsidence and fault movements that slowly crack infrastructure and building foundations, to rapid changes in the ground elevation during severe droughts or flooding caused by hurricanes and storms These current and future GPS stations will provide fundamental observations for studying local ground deformation and minimizing hazards associated with ground instability. These problems can be overcome with the use of a consistent and stable reference frame over time by adopting the same rigorous approach used to describe plate tectonic motions
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