The on-ground data reduction and calibration pipeline for SO/PHI-HRT

TL;DR

This paper describes the design and implementation of an on-ground data reduction and calibration pipeline for the SO/PHI-HRT instrument on the Solar Orbiter, enabling detailed solar magnetic field analysis from raw images.

Contribution

It introduces a ground-based pipeline that enhances onboard processing by providing additional corrections and high polarimetric sensitivity for the SO/PHI-HRT data.

Findings

Pipeline achieves polarimetric sensitivity of 10^{-3}·I_c or better.

Enables reduction of raw images to full Stokes vector.

Supports analysis of solar photospheric magnetic fields.

Abstract

The ESA/NASA Solar Orbiter space mission has been successfully launched in February 2020. Onboard is the Polarimetric and Helioseismic Imager (SO/PHI), which has two telescopes, a High Resolution Telescope (HRT) and the Full Disc Telescope (FDT). The instrument is designed to infer the photospheric magnetic field and line-of-sight velocity through differential imaging of the polarised light emitted by the Sun. It calculates the full Stokes vector at 6 wavelength positions at the Fe I 617.3 nm absorption line. Due to telemetry constraints, the instrument nominally processes these Stokes profiles onboard, however when telemetry is available, the raw images are downlinked and reduced on ground. Here the architecture of the on-ground pipeline for HRT is presented, which also offers additional corrections not currently available on board the instrument. The pipeline can reduce raw images to the full Stokes vector with a polarimetric sensitivity of $10^{-3}\cdot I_{c}$ or better.