Subsidence and Sea-level Rise Measurements for the Northern Gulf of Mexico: An Integrated, Multi-sensor Approach

The combination of remote sensing and ground truth has proven itself especially useful for scientific investigation within the last few decades. Using this approach, this research has investigated ground subsidence and sea-level rise occurring along the northern shore of the Gulf of Mexico. Specifically, this was focused over the areas of Houston and Galveston, Texas and New Orleans, Louisiana. Supporting this investigation were five methods: Interferometric Synthetic Aperture Radar (InSAR), radar altimetry, the Global Positioning System (GPS), tide gauges, and extensometers. Measurements derived from these methods allowed for the creation of velocity maps and local time series spanning the area of interest. This investigation produced the following products:

Twelve (12) 4-pass interferometric-derived velocity maps constructed from raw ERS-1, ERS-2, and Envisat data spanning the years between 1992 and 2012. Twenty-five (25) sea-level anomaly time series from Topex-Poseidon (T/P) and Jason-1 Geophysical Data Records (GDRs) for assessment of absolute sea level change throughout the northern Gulf of Mexico spanning the years between 1992 and 2012. Twenty-eight (28) GPS stations observational data processed for secular trend analysis. Twenty-two (22) tide gauges stations monthly mean sea-level (MSL) records were obtained for secular trend and Fourier analysis. Seven (7) extensometers near Galveston Bay recorded compaction data which was then utilized for secular trend analysis.

Results provided by radar altimetry found multidecadal variability (1992-2012) within expected norms with average rates of absolute sea-level rise bounded between 3 and 4 mm yr-1 within the northern Gulf of Mexico. Therefore, for those regions undergoing high rates of relative sea level rise, the majority is attributed to subsidence. The regions of Houston and Galveston were generally found to be stable. However, Seabrook (on the west side of Galveston Bay) and regions near the inlet of the Houston ship channel (Baytown and Channel View) require continued monitoring due to recent rates of subsidence higher than the surrounding areas and regional norms. The city of New Orleans was found to be stable and experiencing subcentimeter subsidence rates. Areas to the southwest of New Orleans (Houma, New Iberia, Morgan City, and Raceland) and near the peninsula tip were consistently detected by both ground truth and InSAR to be subsiding at rates in excess of 30 mm yr-1. Spatial correlation of the velocity profiles with tectonic and anthropogenic factors allows inferences to be made in regards to the underlying causation mechanism(s).