Operational insights from SPAISE3: initial satellite-based AIS observations over Europe using ground-based digital beamforming

This paper presents the initial results from the SPAISE3 payload, an AIS monitoring system aboard the ALOS-4 satellite, launched in July 2024. Following a successful checkout phase, SPAISE3 began experimental observations in February 2025. The system employs a linear array of eight antennas, with all signal processing, including digital beamforming (DBF), conducted on the ground by leveraging ALOS-4’s high-throughput data downlink. Each antenna element can independently select from conventional AIS channels and newly designated satellite reception channels, offering flexible channel allocation. This study focuses on the first AIS observation campaign over European airspace. We validate the initial performance, specifically analyzing the impact of array configurations and channel assignments on signal reception. We also characterize the challenging radio frequency environment, which is marked by significant external interference, and evaluate its effect on AIS signal acquisition. These preliminary results provide crucial insights into the system’s operational behaviour and the viability of advanced satellite-based AIS monitoring using ground-based DBF. The discussion further explores optimization challenges related to integrating sparse array configurations with diverse channel selections and considers the potential for coordination and expansion among emerging satellite constellations.