OpenSky Report 2025: Improving Crowdsourced Flight Trajectories with ADS-C Data
Junzi Sun, Xavier Olive, Martin Strohmeier, Vincent Lenders
TL;DR
The paper tackles gaps in ADS-B-based flight tracking over oceans and remote regions by integrating ADS-C satellite data from the Alphasat system with OpenSky’s ground-based ADS-B data. It presents a data-fusion approach that links ADS-C updates, which occur every 10–15 minutes, with high-frequency ADS-B positions to reconstruct continuous long-haul trajectories, leveraging a dataset of over 720,000 ADS-C messages from 2,606 aircraft in 2024. The combined dataset improves trajectory accuracy and enables more reliable fuel and CO2 emissions estimates, while revealing flight patterns across Africa that are underrepresented in ADS-B alone. The work highlights both the potential and current limitations of satellite ADS-C coverage and advocates for expanded receiver networks and open data access to support air traffic management, environmental impact assessment, and aviation safety research. Overall, this open-federated approach broadens global flight trajectory visibility and offers a foundation for future methodological and policy developments in open aviation data.
Abstract
The OpenSky Network has been collecting and providing crowdsourced air traffic surveillance data since 2013. The network has primarily focused on Automatic Dependent Surveillance--Broadcast (ADS-B) data, which provides high-frequency position updates over terrestrial areas. However, the ADS-B signals are limited over oceans and remote regions, where ground-based receivers are scarce. To address these coverage gaps, the OpenSky Network has begun incorporating data from the Automatic Dependent Surveillance--Contract (ADS-C) system, which uses satellite communication to track aircraft positions over oceanic regions and remote areas. In this paper, we analyze a dataset of over 720,000 ADS-C messages collected in 2024 from around 2,600 unique aircraft via the Alphasat satellite, covering Europe, Africa, and parts of the Atlantic Ocean. We present our approach to combining ADS-B and ADS-C data to construct detailed long-haul flight paths, particularly for transatlantic and African routes. Our findings demonstrate that this integration significantly improves trajectory reconstruction accuracy, allowing for better fuel consumption and emissions estimates. We illustrate how combined data captures flight patterns across previously underrepresented regions across Africa. Despite coverage limitations, this work marks an important advancement in providing open access to global flight trajectory data, enabling new research opportunities in air traffic management, environmental impact assessment, and aviation safety.