Schoot, Sem, van (2026) Finding the Ionospheric Vertical Total Electron Content Using LOFAR LBA VLBI Calibration Solutions. Bachelor's Thesis, Astronomy.
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Abstract
We present a method to derive Vertical Total Electron Content (vTEC) directly from LOFAR LBA VLBI calibration solutions, providing a clock-error-free alternative to GNSS-based ionospheric models and an independent constraint on absolute ionospheric Faraday rotation for polarization calibration. By combining differential slant TEC (dsTEC) and differential Rotation Measure (dRM) between station pairs with modelled magnetic field values (PPIGRF, via spinifex), we derive closed-form expressions for vTEC at the measured and reference station. The method is validated on two 3C 380 datasets spanning quiet (Kp~1) and mildly disturbed (Kp~3) ionospheric conditions. Baseline length is the dominant factor in reliability: short baselines (≲80 km) between remote and core stations drive the differential magnetic field toward zero, causing vTEC to diverge. Using an international reference station instead (baselines ~200-1000 km) reduces remote-station spread to below 1 TECU and international-station spread to 2-3 TECU. For the disturbed dataset, derived vTEC values converge onto a coherent single-line profile across stations despite magnetic field uncertainties of 50-200 nT, indicating internal precision, though shared systematic uncertainties (static field model, thin-shell approximation, hmF2 choice) mean this does not guarantee absolute accuracy. We regard this agreement as evidence that the method provides a meaningful, independent constraint alongside existing spinifex models.
| Item Type: | Thesis (Bachelor's Thesis) |
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| Supervisor name: | Mevius, M. |
| Degree programme: | Astronomy |
| Thesis type: | Bachelor's Thesis |
| Language: | English |
| Date Deposited: | 02 Sep 2026 08:52 |
| Last Modified: | 02 Sep 2026 08:52 |
| URI: | https://fse.studenttheses.ub.rug.nl/id/eprint/37546 |
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