GRACE(-FO) monthly products are produced routinely using measurements of the orbital motion and the K-Band measurements of the distance between the two satellites. From these solutions, we gained great insight into the water cycle, ice mass balance, and ocean currents for the past twenty years. But these monthly solutions are not the full picture. More information about sub-monthly processes can be extracted from the Level-1B data. Currently, the data used to extract the GRACE-FO orbits contains the K-band ranging (KBR) measurements but not the data from the Laser Ranging Interferometer (LRI). It has been shown several times that using orbits and LRI data, one can calculate residual Line-of-sight gravity signals. These studies mainly focused on the Amazon River region to study changes in the water storage which happen faster than over one month.

We use this approach to look at the changes in the speed of the llulissat glacier in Greenland. This is one of the biggest and fastest glaciers in Greenland and significant changes in its speed can happen over as little as one week during exceptional summer melt periods, as demonstrated a.o. by SAR interferometry. We demonstrate how LRI can help to give further constraints on when these changes in speed happen, within the restrictions of the limited spatial resolution.