Measuring precise sea level from a buoy using the global positioning system

Abstract

High‐accuracy sea surface positioning is required for sea floor geodesy, satellite altimeter verification, and the study of sea level. An experiment to study the feasibility of using the Global Positioning System (GPS) for accurate sea surface positioning was conducted. A GPS‐equipped buoy (floater) was deployed off the Scripps pier at La Jolla, California during December 13–15, 1989. Two reference GPS receivers were placed on land, one within ∼100 m of the floater, and the other about 80 km inland at the laser ranging site on Monument Peak. The position of the floater was determined relative to the land‐fixed receivers using: (a) kinematic GPS processing software developed at the National Geodetic Survey (NGS), and (b) the Jet Propulsion Laboratory's GIPSY (GPS Inferred Positioning SYstem) software. Sea level and ocean wave spectra were calculated from GPS measurements. These results were compared to measurements made with a NOAA tide gauge and a Paros TM pressure transducer (PPT). GPS sea level for the short 100‐m baseline agrees with the PPT sea level at the 1‐cm level and has an rms variation of 5 mm over a period of 4 hours. Agreement between results with the two independent GPS analyses is on the order of a few millimeters. Processing of the longer Monument Peak ‐ floater baseline is in progress and will require orbit adjustments and tropospheric modeling to obtain results comparable to the short baseline.