Land Subsidence Monitoring and Analysis in Louisiana Using GNSS Daily Solutions

Land subsidence affects the vertical control component of the height system in Louisiana at a state-wide level. The National Height Modernization System (NSRS) has been initiated by the National Geodetic Survey (NGS) to enhance the vertical component of the NSRS in the USA. In addition to the positional coordinates, NSRS combines scale, gravity, orientation, and their variation with time. In this study, we estimate and analyze the land subsidence in Louisiana using GNSS data since 2013. We selected 15 well-distributed Continuously Operating Reference Stations over the Louisiana State from the GULFNet network, which is managed by the Center for Geoinformatics at Louisiana State University. The daily GNSS files collected from the GULFNET are processed using an automated procedure to overcome and organize the multi-step tasks. These tasks include the preprocessing (to perform quality control), processing with GipsyX software to obtain the daily solutions, and post-processing to estimate the velocities and the associated uncertainty. In the preprocessing task, various applications are employed to organize and process the raw data files and convert them into RINEX. Final orbits and clocks are also downloaded from JPL in order to obtain the daily solutions with respect to ITRF2014 using GipsyX. Finally, the horizontal and vertical velocities are estimated in time series for all stations and analyzed using the Hector software. The analyzed stations show land subsidence; the highest land subsidence rate (-6.15 mm/yr) is detected in the LMCN station on Louisiana south coast.