Well calibrated space sensor systems for GGOS

From the investigation of GRACE and GRACE-FO instrument data, we are aware of quite a number of unmodeled effects and deficiencies in the calibration of instruments. We want to use these deficiencies as an example to discuss how for a core GGOS observation technique, such as GRACE / GRACE-FO, all opportunities to assess and improve sensor calibration and to identify and characterize unmodeled effects affecting the measurements should be explored. This may seem obvious, but we will show that a major effort on this field would be very desirable. We deliberately choose the GGOS session for a broader discussion of the topic, and we want to highlight the importance of an overarching approach that combines insight from different satellite missions and space techniques.