AFD: A Practical Tool for FTP-Based GNSS Data Acquisition and Preprocessing

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This study introduces the Automatic File Downloader (AFD), a MATLAB-based software developed for the efficient retrieval and organization of GNSS data. The need for this tool arose from the limitations of the existing VIP.m software, which became obsolete due to protocol incompatibilities, outdated data addresses, and a static user interface. AFD was designed with a modular and extensible architecture that supports FTP and HTTP protocols, automatic date conversions, dynamic file classification, and robust error handling. The software enables seamless downloading of GNSS datasets from international data centers such as IGS, IGL, and CODE, and automatically prepares the files for processing with scientific analysis tools like the Bernese GNSS Software. Comparative testing demonstrated that AFD provides faster, more reliable, and user-friendly performance compared to its predecessor. With its flexible architecture and scalable design, AFD represents a sustainable solution for researchers and engineers working with GNSS data, offering significant improvements in automation, accuracy, and usability. Unlike previous tools such as VIP.m, which relied on fixed directory structures and lacked adaptability to evolving data sources, AFD introduces a protocol-flexible and configuration-driven architecture that enables long-term sustainability. Moreover, this study fills a documented gap in the GNSS data processing literature by providing an open, extensible, and automation-oriented preprocessing workflow that integrates directly with commonly used scientific analysis environments. In this respect, AFD contributes a novel, practical, and maintainable solution that strengthens GNSS data acquisition pipelines in both research and operational applications.