Impact of GRACE-FO LRI and the updated accelerometer transplant product (ACH1B) on the estimated static Earth gravity field

The impact of the GRACE-FO Laser Ranging Interferometer (LRI) and the updated transplant product ACH1B is evaluated on the static part of the Earth gravity field by solving the gravity field determination problem with the least-squares estimation approach.

In order to evaluate the impact of the LRI (first application) and the ACH1B product (second application), the type of observation sets is based on the range-acceleration measurements derived from the LRI and the K-Band Ranging (KBR) systems of the GRACE-FO satellites and from the LRI system only respectively.

The type of solution selected for the two applications is the approximate solution of the acceleration approach. The Earth gravity field used as reference is the GOCO06s model truncated to degree and order 120.

Two monthly observation sets are created per application by correcting the LRI/KBR range-acceleration measurements with:

• the light time correction (LTC) for LRI and KBR
• the antenna offset correction (AOC) for KBR only
• the “accelerations correction term” (ACT) which includes the line-of-sight (LOS) relative accelerations caused by the solid Earth tides, the ocean tides, the third body attraction, the non-gravitational forces and the effect of general relativity
• the “correction term” (CT) which includes the impact of the residual centrifugal acceleration (Ghobadi-Far K, et al., 2018)
• outliers removal

The above described data processing, leads to range-accelerations which include the effect of the Earth's gravitational forces only. For the calculation of the LOS relative accelerations of the ACT, a modified version of the “High Precision Orbit Propagator” software developed by (Mahooti, 2022) is applied with the exception of the LOS relative accelerations caused by the non-gravitational forces.

The aforementioned accelerations are derived by using the ACT1B product only for both of the observation sets of the first application and for the first observation set of the second application. The ACT1B (for GRACE C satellite) and the ACH1B (for GRACE D satellite) products are used for the second observation set of the second application.

After performing the gravity field determination by using each of the two observation sets per application, the square root of the degree difference variances (DDVs) between the datasets and the GOCO06s model and the datasets themselves are examined on the high-frequency domain from which promising results are derived regarding the impact of the LRI and the new ACH1B product on the static Earth gravity field.