Since 1978, the Harris-Galveston Subsidence District (HGSD), in collaboration with the National Geodetic Survey (NGS) and other state to local agencies, has performed surveys, such as spirit leveling and global positioning system (GPS) releveling, to understand the vertical movement of benchmarks in the region. Large-scale releveling surveys were conducted in 1978, 1987, 1995, 2000, and 2007. These surveys provided elevation data in the respective epoch that were accepted and published in the NGS database.
As the NGS began work on the National Spatial Reference System (NSRS) Modernization in 2020 to replace all current horizontal reference frames and vertical datums with new terrestrial reference frames and a geopotential datum, the NGS accepted less than one percent of existing benchmarks in the Houston-Galveston region due to subsidence. As a result, the surveying efforts in this region are greatly diminished as significantly less benchmarks are available.
To uphold the surveying legacy and assist the NGS with recent elevation data, the HGSD initiated the 2022 global navigation satellite systems (GNSS) survey. This survey involved the reoccupation of over 140 benchmarks across 10 counties in Southeast Texas in less than one month. All benchmarks were processed in OPUS Projects, according to NGS standards and specifications, and were published in NGS’s Integrated Database.
THE GOALS OF THE 2022 GNSS SURVEY INCLUDE:
- Updated (2022 epoch) elevation data obtained at each benchmark.
- Enhancement of NSRS Modernization efforts and acceptance into NGS Integrated Database.
- Benchmark availability for the surveying community.
- Usability in other HGSD research projects.