Achieving Consistent Doppler Measurements from SDO/HMI Vector Field Inversions

TL;DR

This paper presents a three-stage correction procedure that significantly reduces orbital artifacts in SDO/HMI Doppler measurements, enhancing data consistency and scientific utility.

Contribution

The paper introduces a novel, easily implemented three-stage method to mitigate orbital artifacts in HMI Doppler data, improving data quality for solar studies.

Findings

Orbital artifacts reduced by 31dB in power.

Corrected data show improved temporal and spectral properties.

Procedure enhances data consistency without introducing new artifacts.

Abstract

NASA's Solar Dynamics Observatory is delivering vector field observations of the full solar disk with unprecedented temporal and spatial resolution; however, the satellite is in a highly inclined geostationary orbit. The relative spacecraft-Sun velocity varies by $\pm3$~km/s over a day which introduces major orbital artifacts in the Helioseismic Magnetic Imager data. We demonstrate that the orbital artifacts contaminate all spatial and temporal scales in the data. We describe a newly-developed three stage procedure for mitigating these artifacts in the Doppler data derived from the Milne-Eddington inversions in the HMI Pipeline. This procedure was applied to full disk images of AR11084 to produce consistent Dopplergrams. The data adjustments reduce the power in the orbital artifacts by 31dB. Furthermore, we analyze in detail the corrected images and show that our procedure greatly improve the temporal and spectral properties of the data without adding any new artifacts. We conclude that this new and easily implemented procedure makes a dramatic improvement in the consistency of the HMI data and in its usefulness for precision scientific studies.