Magnetic Splinter Meeting

ASM inter-satellite comparison

VFM calibration: Swarm A residual analysis in-flight determination of 18 VFM parameters, including temperature dependencies

Model of VFM perturbation field (responsible for ASM-VFM residuals) Determining the Sun vector Ecliptic Plane Earth Spin (23.5˚) Summer Solstice X Z Spacecraft Quaternion Inertial Space Ecliptic Plane Sun Aligned 𝑣 𝑠𝑢𝑛 = 𝑞 𝑠/𝑐 −1 𝑡 ∙ 𝑀 𝐶𝐼𝑆 −1 𝑡 ∙ 𝑀 𝐸𝑂 −1 ∙ 𝑀 𝑆𝐴 −1 𝑡 ∙ 𝑛 𝑥 Sun vector in baffle Max sun absorption angle 𝑣 𝑏𝑎𝑓 = 𝑟 𝜃 𝜑 = 𝑠𝑖𝑛 𝛼 0 𝑐𝑜𝑠 𝛼 0 1 0 𝑐𝑜𝑠 𝛼 0 −𝑠𝑖𝑛 𝛼 ∙ 𝑣 𝑠𝑢𝑛 𝛼=70° Flight direction Baffle Heat model 𝐵𝑎𝑓 𝑚𝑜𝑑𝑒𝑙 = 0 𝑒𝑐𝑙𝑖𝑝𝑠𝑒 0 𝜃<0 𝑠𝑖𝑛 4 𝜑 ∙ 𝑠𝑖𝑛 4 𝜃 𝑒𝑙𝑠𝑒

Comparing Model predictions with observations Measurements Simulation

Kursk anomaly against MF7 100 90 MF7 degree 60

Kursk anomaly against MF7: gradients } 100 0.2 nT 90 MF7 degree 60

NGDC Main field model (based on NEC data) Swarm B residuals with MF7 subtracted X Y Z rms = 6.4 nT rms = 12.7 nT rms = 3.2 nT

BGS Field Modelling (based on NEC data) Swarm Z misfits Misfit statistics Satellite mean std dev X -0.42 30.47 Y -0.04 21.48 Z 0.75 19.92 Observatory X -0.07 5.96 Y -0.07 3.77 Z -0.06 3.73

Euler angle determination, 3 day, adjusted offsets X axis looks fine Y axis: Swarm A drifting off at about 1 arcsec/10 days Z axis Swarm B: 25 arcsec shift. Does toroidal magnetic field change by 8 nT with altitude?

Field Modeling and Euler angle estimation (based on VFM + STR data) sun lower than +10 above horizon

Variation of inter-boresight angle, Swarm C

Summary ASM-VFM perturbation VFM calibration “empirical model” (GFZ) “engineering model” (DTU) Provide perturbation model predictions Merging of the two models ASM vector data: Provision of more data for Cal/Val activities VFM calibration Estimate VFM parameters using night/corrected data (ESA) … after applying empirical correction from GFZ … after applying “engineering model” prediction from DTU Co-estimation of perturbation model and VFM calibration parameters Updated L1b data with new Euler angles Replace pre-flight values with in-flight determined (which?) ones IGRF team needs updated L1b data by 1 August 2014 for IGRF determination Need for more information (e.g on flags, “ASM-VFM perturbation” tasks, …) data rejection based on which flags / thresholds Sharing of information, coordination, documentation of data sets

Estimation of static Euler angles (DTU) “dark regions”, but including “twilight data”: sun lower than +10 above horizon SW-A SW-B SW-C a 11.8042 -8.8847 1.8130 b -76.1903 -76.4266 -76.8269 g -12.5736 9.1141 -1.9789 In-flight (degrees): SW-A SW-B SW-C a 11.8294 -8.9132 1.7931 b -76.1904 -76.4241 -76.8270 g -12.5941 9.1525 -1.9536 Pre-flight (degrees): SW-A SW-B SW-C Da 23.2 -25.1 -16.3 Db 4.6 4.9 0.2 Dg 14.6 38.8 21.1 Difference (arcsecs)

Estimation of static Euler angles (GFZ) SW-A SW-B SW-C a 11.8237 -8.8947 1.7727 b -76.1848 -76.4171 -76.8229 g -12.5827 9.1799 -1.9386 In-flight (degrees): SW-A SW-B SW-C a 11.8294 -8.9132 1.7931 b -76.1904 -76.4241 -76.8270 g -12.5941 9.1525 -1.9536 Pre-flight (degrees):