Earth’s gravity field modelling based on satellite accelerations derived from onboard GPS phase measurements

Abstract

GPS data collected by satellite gravity missions can be used for extracting the long-wavelength part of the Earth's gravity field. We propose a new data processing method which makes use of the 'average acceleration' approach to gravity field modelling. In this method, satellite accelerations are directly derived from GPS carrier phase measurements with an epoch-differenced scheme. As a result, no ambiguity solutions are needed and the systematic errors that do not change much from epoch to epoch are largely eliminated. The GPS data collected by the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite mission are used to demonstrate the added value of the proposed method. An analysis of the residual accelerations shows that accelerations derived in this way are more precise, with noise being reduced by about 20 and 5% at the cross-track component and the other two components, respectively, as compared to those based on kinematic orbits. The accelerations obtained in this way allow the recovery of the gravity field to a slightly higher maximum degree compared to the solution based on kinematic orbits. Furthermore, the gravity field solution has an overall better performance. Errors in spherical harmonic coefficients are smaller, especially at low degrees. The cumulative geoid height error is reduced by about 15 and 5% up to degree 50 and 150, respectively. An analysis in the spatial domain shows that large errors along the geomagnetic equator, which are caused by a high electron density coupled with large short-term variations, are substantially reduced. Finally, the new method allows for a better observation of mass transport signals. In particular, sufficiently realistic signatures of regional mass anomalies in North America and south-west Africa are obtained.

Gravity Field Model Determination Based on GOCE Satellite Point-Wise Accelerations Estimated from Onboard Carrier Phase Observations

“…In addition, we subtracted reference accelerations computed with the model DGM-1S [41] from the differential accelerations to obtain residual accelerations. Then, the residual accelerations exceeding three times the corresponding standard deviations were identified as outliers and discarded according to the method used in Guo et al [25]. The corresponding standard deviations were estimated based on the method with five iterations, and they were 1.12, 0.81 and 1.90 mGal, respectively, for the three components of the carrier phase-derived accelerations.…”

“…An alternative method is to numerically differentiate the GPS carrier phase observations then obtain both the range rate and range acceleration, which is called the carrier phase differentiation method. This method has been successfully applied in airborne gravimetry [23,24] and satellite gravimetry [25]. The most prominent advantage of this approach is the avoidance of the cycle ambiguity problem and the elimination of systematic errors (e.g., hardware delays from the receiver and GPS satellites) that are common to adjacent epochs [23,25].…”

“…Guo et al [25] adopted the average acceleration approach to recover the gravity field model from satellite accelerations derived from onboard GPS phase measurements. It was shown that the noise of the accelerations derived by the carrier phase differentiation method was lower than that derived by the orbit differentiation method in all three components, especially in the cross-track component, which showed an improvement of about 20%.…”

“…Thus, the recovered gravity field based on the carrier phase differentiation accelerations had a slightly higher accuracy when compared with the solution based on the orbit differentiation method. It should be noted that Guo et al [25] estimated the average satellite accelerations in two steps: first, the position differences epoch by epoch were derived directly from the GPS carrier phase measurements; the average satellite accelerations were then obtained with the position differences.…”

“…In this study, we proposed to recover the gravity field model based on the point-wise accelerations of the GOCE satellite estimated by the carrier phase differentiation method from the onboard carrier phase observations. This idea has not yet been addressed and differs from the average acceleration approach used for gravity field modeling and the approach of estimating the satellite accelerations in Guo et al [25]. The paper is organized as follows.…”