Comparison between Laser Ranging Interferometer and K/Ka band Ranging instruments.

The GRACE Follow-On mission is the first twin-satellite mission equipped with a laser ranging interferometer (LRI) to measure the inter-satellite distance between the pair of satellites. The LRI operates independently of the K/Ka-band interferometer (KBR) and uses wavelengths 10⁴ times shorter than the K-band system.  Released at the end of July 2019, the LRI range data is therefore expected to be of higher accuracy than the KBR and offers the possibility of a better spatial resolution. We compare the LRI and KBR observations of the GRACE-FO mission, from launch to December 2019, to assess the quality of the new LRI system. Spectral analysis of the level1B data shows that the noise level of the LRI is 3 orders of magnitude smaller than the KBR and that the gravity signal can be detected in the spectral band up to 30mHz in the LRI data compared to 20mHz in the KBR data.  We compare gravity fields estimated using LRI and KBR and show which parts of the spherical harmonic spectrum are affected by the improved accuracy of the LRI observations.