MAGNETIC VECTOR DISTURBANCE MODEL AND CORRECTION OF SWARM

MAGNETIC VECTOR DISTURBANCE MODEL AND CORRECTION OF SWARM DATA by Lars Tøffner-Clausen with inputs and support from Vincent Lesur, Peter Brauer, Nils Olsen, and Chris Finlay 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Outline • Roadmap to corrected magnetic data for Swarm • Maps of magnetic disturbance vector • Changes to VFM processing parameters • Elements added to Swarm Level 1 b magnetic products • Conclusions 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

The Swarm Vector Magnetometer (VFM) a Quick-Guide • Total: 9 parameters 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Scalar Calibration: Estimate 9 Parameters Swarm Alpha – All Data 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Add Temporal Parameter, st 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Solar Induced Disturbance Careful analysis (by members of the ASM-VFM Residual Task Force) of the residuals displayed on the previous figure show a clear correlation between the disturbance and the Sun incident angle on the spacecraft. Empirical modelling of the disturbance vector using spherical harmonics in the Sun incident angles α and β (shown on the right) have proven quite successful. 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Estimation of d. BSun Added 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Added Correction of s. Tsensor Not linear in time 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Polynomial Scaling in Time 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Temporal Scaling Factor 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Final Scalar Residuals, Swarm Alpha 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Maps of d. BSun 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Parameterisation, Summary Parameters 2028 3 • d. BSun: Static SH model, degree 25, incl. constant term • Non-orthogonalities • Scale • Dependent on sensor temperature (x- and z-axes), s. Tsensor 2 • Dependent on Sun inclination angle (x- and z-axes), sβ 2 • Temporal evolution (semi-common for all three axes) 6 modeled as order 3 B-spline – piece-wise parabolic Total 2041 Solved using truncated singular value decomposition with ~700 degrees of freedom 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Scaling Parameters Sat Sensitivity/sensor temperature, Sensitivity/Sun s. T, sensor elevation, sβ [10 -6/n. T °C] Pre-flight Adjustment [10 -6/n. T deg] Value Non-orthogonalities [arc-seconds] Pre-flight Adjustment A 28. 5 28. 8 28. 3 0. 616 0. 780 0. 944 -0. 125 0 0. 012 102. 386 217. 403 -179. 318 -0. 601 -3. 960 0. 149 B 28. 3 29. 0 28. 8 1. 168 1. 384 1. 602 -0. 132 -0. 003 -0. 198 350. 880 62. 432 -147. 060 -0. 558 -2. 453 1. 607 C 27. 7 29. 1 28. 4 1. 521 1. 300 1. 076 -0. 090 -0. 038 -0. 167 139. 140 -248. 890 -109. 960 0. 094 1. 042 0. 080 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Parameters Added to Level 1 b Products • d. B_Sun Magnetic stray field correction vector of Sun induced stray field, VFM frame • alpha, beta (only Mag-C product) Sun inclination angles: alpha: rotation about –y axis beta: angle to –y axis • B_pre (only Mag-C product) Pre-calibrated VFM magnetic field vector, VFM frame 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F

Conclusions • Established and implemented model for correcting magnetic data Reduces scalar residuals between ASM and VFM to below 175 p. T • Preliminary model – current issues: • Adjustments of VFM pre-flight calibration parameters disputed • Poor determination of y-axis related parameters • Disturbance propagation effect (time-filter) not accounted for • Lack of physical explanation for Sun dependent scaling, sβ • … and more ? 5 th Swarm Data Quality Workshop Session 2 M, 8 September 2015 IPG Paris/F