Visible-light channel of the Metis/Solar Orbiter coronagraph: On-ground polarimetric calibration
Bibliographic record
Abstract
Context. Metis is the solar coronagraph on board the ESA/NASA mission Solar Orbiter (SolO), launched in 2020. It is designed to acquire simultaneous images of the solar corona in visible polarized light (580−640 nm), and in the narrowband H I Lyman- α line (i.e., 121.6 nm). The instrument visible-light channel includes a polarimeter composed of two liquid crystal variable retarder (LCVR) cells, a quarter-wave plate, and a linear polarizer, with the LCVR cells acting as the modulating element. By applying a specific voltage to the cells, it is possible to modify the incoming polarized light by changing the direction of the associated vector by a known angle, i.e., the angle of retardance. Aims. The polarimetric characterization of Metis is needed to correctly derive the properties of the plasma in the observed solar corona. This work describes the steps we took to fully characterize the visible channel of the Metis coronagraph, i.e., by deriving the modulation and demodulation matrices for each pixel, the latter being the key element for deriving the Stokes vector of the observed K corona. We completed the characterization by deriving the error associated with the derived values. Methods. The first step is to fully characterize the Metis polarimeter. This is needed to derive the relation between the voltage applied to the liquid crystal cells and the angle of retardance imposed on the incoming polarized light. This step represents the starting point for the calibration of the full instrument. Results. We derived (i) the voltage versus retardance curve associated with the polarimeter and (ii) the demodulation tensor of the Metis coronagraph, which is now used to retrieve the Stokes vector that describes the coronal light polarization state. Conclusions. This calibration is fundamental to disentangle the coronal light from the instrumental effects, such as disuniformity and instrumental polarization.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".