# Comprehensive Determination of the Hinode/EIS Roll Angle

## TL;DR

This paper introduces a new method to accurately determine and correct the roll angle of the Hinode/EIS instrument by cross-correlating its data with AIA images, improving data alignment.

## Contribution

The paper presents the first systematic measurement of the EIS roll angle and provides a software tool for improved coalignment of EIS data.

## Key findings

- Estimated average roll angle of -0.387 degrees with high precision.
- Method applied to 3336 rasters with high signal-to-noise ratio.
- Software implementation available for broader use.

## Abstract

We present a new coalignment method for the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft. In addition to the pointing offset and spacecraft jitter, this method determines the roll angle of the instrument, which has never been systematically measured, and is therefore usually not corrected. The optimal pointing for EIS is computed by maximizing the cross-correlations of the Fe XII 195.119 \r{A} line with images from the 193 \r{A} band of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). By coaligning 3336 rasters with high signal-to-noise ratio, we estimate the rotation angle between EIS and AIA and explore the distribution of its values. We report an average value of (-0.387 $\pm$ 0.007)\deg. We also provide a software implementation of this method that can be used to coalign any EIS raster.