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Abstract

Integer ambiguity resolution (IAR) is critical for improving the accuracy of GPS-derived orbit and Earth gravity field. However, the application of undifferenced IAR in the data processing for the low earth orbit (LEO) satellite has not been discussed yet. To this end, 1-year GPS data and accelerometer observations onboard the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellites are processed with the undifferenced IAR method. GRACE-FO satellite orbit and monthly time-variable Earth gravity field are determined simultaneously with the fixed GPS constellations. Initial results have demonstrated the efficiency of the method. The 3-Dimensional (3D) root-mean-square (RMS) of the generated orbit reaches 1.5 cm with the Jet Propulsion Laboratory (JPL) reduced-dynamic orbit as reference. The RMS of satellite laser ranging (SLR) and K-band ranging (KBR) residuals are well below 1.5 cm and 0.5 cm, respectively. In the single-satellite mode, significant improvement on Earth gravity field is noticed. Long wavelength signatures of our Earth gravity field are recovered with a similar quality as achieved with twin GRACE-FO observation data. While in the double-satellite mode, benefits of undifferenced IAR are subtle with mm-level KBR measurements involved. In general, the undifferenced IAR method can be treated as a powerful tool in both orbit determination and gravity field recovery. Further investigations on simultaneous estimation of orbit and gravity field are to be assessed with carrier-range observations obtained from undifferenced IAR.