Earth's gravity field to the eighteenth degree and geocentric coordinates for 104 stations from satellite and terrestrial data

Geodetic parameters describing the earth's gravity field and the positions of satellite-tracking stations in a geocentric reference frame have been computed. These parameters were estimated by means of a combination of five different types of data: routine and simultaneous satellite observations, observations of deep space probes, measurements of terrestrial gravity, and surface triangulation data. The combination gives better parameters than does any subset of data types. The dynamic solution used precision-reduced Baker-Nunn observations and laser range data of 25 satellites. Data from the 49-station National Oceanic and Atmospheric Administration BC-4 network, the 19-station Smithsonian Astrophysical Observatory Baker-Nunn network, and independent camera stations were employed in the geometrical solution. Data from the tracking of deep space probes were converted to relative longitudes and distances to the earth's axis of rotation of the tracking stations. Surface gravity data in the form of 550-km squares were derived from 19,328 1° × 1° mean gravity anomalies. The surface triangulation data consisted of the datum coordinates of each tracking station. Coordinates and potential coefficients were derived separately for each iteration. The adopted solution in each iteration was a combination solution chosen to improve the residuals of all data types. In addition to these five data sets an independent test of the solution utilized sea level heights plus satellite-tracking and surface gravity data not used in the combination. The total gravity field is represented by spherical harmonic coefficients complete to degree and order 18 and a number of higher degree terms. The half-wavelength resolution of this global solution subtends about 10° at the earth's center. The accuracy of the global gravity field has been estimated as ±2.5 m in geoid height, or 64 mGal2. Coordinates of the fundamental laser stations are determined with an accuracy of 2–4 m, and those of the fundamental optical network, with an accuracy of 5–10 m. The best-fitting ellipsoid has a flattening ƒ of 1/ƒ = 298.256 ± 0.001 and a semimajor axis ae = 6378140.4 ± 1.2 m.