ESA UNCLASSIFIED – For Official Use Christian Siemes Swarm Data Quality Workshop , Potsdam, Germany Swarm ACC and GPSR summary

Temperature dependency Fast disturbances (steps, spikes, …) Problem 1: Temperature correction model established, but estimating its parameters remains challenging (even for good periods without steps) Problem 2: Step detection algorithm established, correction algorithm pending ACC summary

Swarm A measures the same as Swarm C, but with much smaller scale obscured by higher noise skewed by temperature effect ACC on Swarm C is best

ACC summary Way forward Processing Use POD-derived accelerations in estimation of temperature correction  Caveat: No possibility to validate temperature correction Occurrence of spikes and steps in Swarm C seems to vary over time  Investigate why good periods are good For L2 density product, focus on Swarm C ACC data Spacecraft Optimization of the ACC thermal environment Scale factor calibration by ACT activations (under discussion) Release L1b and/or L2 data to cal/val users with flaws (discussion needed, user demand)

ESA UNCLASSIFIED – For Official Use GPSR summary

Activated: Antenna + receiver corrections Carrier smoothing algorithm Phase residuals 9.8 mm Code residuals 40 cm Deactivated Antenna + receiver correction Carrier smoothing algorithm Phase residuals 8.4 mm Code residuals 43 cm Note: Impact on orbit negligible GPSR summary

SLR validation of reduced-dynamic orbit (< 2 cm when PCV map used)

GPSR summary Differences at 10 cm level Quality of kinematic orbits varies in time probably due to ionosphere Clear improvement of kinematic orbits due to 1 Hz GPS data Fit between kinematic and reduced-dynamic orbits

GPSR summary

Significant increase in carrier-phase residuals during last few months

Monthly gravity field solutions Coloured: Swarm Black: GRACE (GPS only) 6 months ago in Copenhagen Today in Potsdam GPSR summary

Some features easier to remove with 1 Hz data GPSR summary

Swarm reduced-dynamic orbits are of good quality (SLR fit < 2 cm) Quality of Swarm kinematic orbits is worse, especially close to geomagnetic poles and equator (3D fit of ~10 cm with reduced-dynamic orbits) Quality of Swarm kinematic orbits improves with 1 Hz GPS data Large increase in GPS phase residuals during last few months probably related to ionospheric activity Data screening of GPS data based on high ionospheric variability has only marginal effect on the orbit Gravity field models benefited from better processing and receiver settings GPSR summary

Way forward Further optimization of receiver (under discussion) Prevent LossOfSync events  Continuous time information, in particular for ASM Reduce the number of GPS SVs required to invoke the Kalman filter based PVT calculation from 3 to 1 Activate the fast re ‐ acquisition of the L1 carrier Orbit improvement Increase the carrier loop bandwidth for the L2 carrier tracking loop Link between tracking loop bandwidth and antenna FoV Complexity of changes and system impact under investigation Which changes can be implemented with/without interruption of nominal operations? (GPSR  AOCS) Further improvement of processing GPSR summary