Dynamic sea surface topography, gravity, and improved orbit accuracies from the direct evaluation of Seasat altimeter data

Abstract

A gravitational model incorporating Seasat altimetry, surface gravimetry, and satellite tracking data has been determined in terms of global spherical harmonics complete to degree and order 50. This model, PGS‐3337, uses altimeter data as a dynamic observation of the satellite's height above the sea surface. A solution for the ocean's dynamic topography is recovered simultaneously with the orbit parameters, gravity, and ocean tidal terms. The recovered dynamic topography reveals the global long wavelength circulation of the oceans with a resolution of 2000 km and is very similar to the mean upper ocean dynamic height derived from historical ship observations. The PGS‐3337 geoid has an uncertainty of 60 cm rms globally but only 25 cm rms over the ocean because of the altimeter measurements. Seasat orbits determined in this solution have an estimated accuracy for the radial position of 20 cm rms. The difference between the altimeter observed sea height and the geoid plus dynamic topography model is 30 cm rms. Contained in these residuals are the sea height variability, as well as errors from the geoid, orbits, tidal models, and altimeter range measurement. This performance level is 2 to 3 times better than that achieved with previous Goddard gravitational models.

Comparison of geosat and gravimetric geoid profiles in the North Sea

“…The long-wavelength geoid features were subsequently restored by fitting the average geoid height profile to a geoid profile defined by the PGS-3337 geopotential model complete to degree 40 (Marsh et al, 1989;Haines et al, 1990;Schum et al, 1990). Therefore, when comparing Geosat profiles and the terrestrial gravimetric geoid, it is expected that some very-long-wavelength differences (> 1,000 km) could remain, which represent the differences between OSU91A and PGS-3337 up to spherical harmonic degree and order 40.…”

Along-track gravity anomalies from Geostat and Seasat altimetry: GEBCO overlays

“…The long wavelengths ( > 1000 km) are first removed by subtracting a spherical harmonic model (Marsh et al, 1990) of the gravity field complete to degree and order 40 from the along-track vertical deflection. To suppress the short wavelength noise, a Gaussian shaped low-pass filter was convolved with each profile.…”

A combined theory for zonal harmonic and resonance perturbations of a near-circular orbit with applications to COSMOS 1603 (1984-106A)

“…A comparison of the (~, 7) derived harmonics with three NASA gravity field models, GEM-T 1 (Marsh etal., 1988), GEM-T2 (Marsh etal., 1989) and PGS-3337 (Marsh et al, 1990) are presented in Table II, with results from the eccentricity taken from Paper 1.…”

“…Furthermore the residuals are significantly larger than the observed accuracites which varied between 2 x 10 -6 and 16 x 10 -6 (Paper 1). Apparently, although the simplistic modelling for the zonal variation is adequate qualitatively, the neglect of higher order terms in Equation (5) (Marsh et al, 1988), GEM-T2 (Marsh et al, 1989) and PGS-3337 (Marsh et al, 1990). 46960 when the eccentricity was close to its minimum value.…”