# EHT-HOPS pipeline for millimeter VLBI data reduction

## TL;DR

This paper introduces an automated pipeline for calibrating and reducing millimeter VLBI data, improving imaging quality for high-resolution astronomical observations by addressing atmospheric and array heterogeneity challenges.

## Contribution

The authors develop a new automated data reduction pipeline based on HOPS, tailored for millimeter VLBI, enabling better calibration and imaging for astronomical research.

## Key findings

- Pipeline successfully tested on 86 GHz GMVA data with ALMA.
- Enhanced calibration improves image quality over classical methods.
- Supports standard data formats for astronomical analysis.

## Abstract

We present the design and implementation of an automated data calibration and reduction pipeline for very-long-baseline interferometric (VLBI) observations taken at millimeter wavelengths. These short radio-wavelengths provide the best imaging resolution available from ground-based VLBI networks such as the Event Horizon Telescope (EHT) and the Global Millimeter VLBI Array (GMVA), but require specialized processing due to the strong effects from atmospheric opacity and turbulence as well as the heterogeneous nature of existing global arrays. The pipeline builds upon a calibration suite (HOPS) originally designed for precision geodetic VLBI. To support the reduction of data for astronomical observations, we have developed an additional framework for global phase and amplitude calibration which provides output in a standard data format for astronomical imaging and analysis. We test the pipeline on observations taken at 3.5 mm (86 GHz) by the GMVA joined by the phased Atacama Large Millimeter/submillimeter Array in April 2017, and demonstrate the benefits from the specialized processing of high frequency VLBI data with respect to classical analysis techniques.