Improving the Solar Transverse Magnetic-field Measurement Accuracy with Dual-perspective Stereoscopy Using SO/PHI-HRT and SDO/HMI

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Abstract
Accurate photospheric transverse magnetic fields are crucial for solar-activity studies and coronal field modeling but are often limited by lower signal-to-noise ratios and the 180° azimuth ambiguity. We present an observational validation of a dual-perspective stereoscopic approach that reconstructs an improved transverse component in the Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) reference frame using only line-of-sight (LOS) magnetograms from SDO/HMI and the Solar Orbiter Polarimetric and Helioseismic Imager High Resolution Telescope (HRT). Using a coobservation on 2024 October 9 with a separation angle α ≈ 54 . ° 46, we develop a dedicated processing pipeline including solar-rotation compensation, reprojection onto a common grid, resolution homogenization, and tile-based fine coregistration. After applying the 2D stereoscopic relation to the coregistered LOS fields, we obtain the reconstructed transverse component. From weak-field statistics of the analyzed transverse component, the reconstructed field reaches a robust width (median absolute deviation (MAD)) of σ MAD new ≈ 9.5 G, substantially below those of the instrument-provided transverse components, σ MAD HMI ≈ 83.2 G and σ MAD HRT ≈ 62.3 G, bringing the transverse-component uncertainty to the same order as the LOS uncertainty. Direction-consistency tests show 93.5% agreement with the minimum-energy-based (ME0) disambiguation of the HRT transverse field and 99.9% agreement above the ME0 noise threshold. We further demonstrate that the method remains effective when applied to the higher-cadence hmi.M_45s LOS magnetograms, enabling high-cadence, LOS-precision, transverse-field estimates.
Funding Information
  • MOST ∣ National Key Research and Development Program of China (2022YFF0503004)
  • MOST ∣ National Key Research and Development Program of China (2021YFA1600504)
  • MOST ∣ National Key Research and Development Program of China (2020YFC2201200)
  • MOST ∣ National Natural Science Foundation of China (12333009)
  • MOE ∣ Fundamental Research Funds for the Central Universities (KG202506)

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