Analysis of GRACE Follow-On laser ranging interferometer measurements for time-variable (sub-monthly) and static gravity signals

Abstract:

The GRACE Follow-On mission, launched on 22 May 2018, is continuing the legacy of GRACE for measuring the Earth gravity field and its temporal variations caused by mass redistribution in the Earth system. In addition to the baseline K-band microwave ranging (KBR) system, GRACE Follow-On is equipped with a laser ranging interferometer (LRI), which is a technical demonstration element of the mission and measures inter-satellite distance change with much higher precision than the KBR system. Since the initial turn on of LRI in mid-June 2018, it has successfully measured the inter-satellite ranging data with a noise level of 1 nm/√Hz at frequencies above 100 mHz. In spite of substantially different measurement noise characteristics, monthly-mean gravity fields estimated from KBR and LRI data result in solutions with comparable quality. This is due to temporal aliasing of high-frequency un-/mis-modeled mass change signals into the mean fields. Such temporal aliasing error still exceeds the KBR and LRI sensor noise. In this presentation, we show a new approach to analyze the inter-satellite LRI measurements for gravitational perturbation along the satellite orbit and evaluate their signal and error characteristics in comparison to KBR observations as well as various Earth gravity field models. We present examples of sub-monthly time-variable gravity change and short wavelength static gravity signals from the improved LRI measurements.