Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRSmarter, more robust, connected: With ASTONISH Towards the Next Generation of Airspace Surveillance
The EU research project ASTONISH is developing technological alternatives to traditional radars and transponder systems. It focuses on passive radar systems, alternative communication pathways, and integrated sensors. The Fraunhofer-Institute for High Frequency Systems and Radar Techniques FHR contributes its expertise, particularly in the area of LDACS-based passive radar solutions.
What might modern, resilient monitoring of civil air traffic look like in the future, even when established systems fail or reach their limits? This question is addressed by the European research project ASTONISH (Alternate Surveillance Technologies for Innovative Solutions), which has been funded since 2024 as part of SESAR 3 JU research and innovation programme and Horizon Europe. The goal is to develop innovative, scalable alternatives to traditional radar and transponder systems that can be integrated into the European air traffic control landscape -economically, efficiently, and with a forward-looking approach.
The Fraunhofer Institute for High-Frequency Physics and Radar Technology FHR is collaborating here with international partners—including ENAV S.p.A. (Italian Air Navigation Service Provider, Italy), DLR (Deutsches Zentrum für Luft- und Raumfahrt | German Aerospace Center, Germany), Collins Aerospace (Ireland), CIRA (Centro Italiano Ricerche Aerospaziali | Italian Aerospace Research Center, Italy), the University of Naples Federico II (Italy), and CATEC (Centro Avanzado de Tecnologías Aerospaciales | Advanced Center for Aerospace Technologies, Spain) - on three technological pillars: ground-based surveillance (ground based systems), aircraft-based alternative surveillance (A-SUR), and integrated sensor systems for airport operations. Dr. Diego Cristallini, Head of the Passive Sensor Network group at Fraunhofer FHR, and his team are contributing to the research and development of the work package related to ground-based surveillance.
Passive Radar Instead of Primary Radar—Cost-Effective and Robust
Traditional primary radars are expensive to procure, complex to operate, and are therefore in a decommissioning phase in many countries. For this reason, ASTONISH focuses on passive multistatic radar systems that evaluate existing signals from the environment—such as those transmitted over the new LDACS system (L-band Digital Aeronautical Communications System). These stations, originally designed for air-ground communication, emit LDACS signals, the reflections of which can be detected by a network of receiving stations on aircraft. The major advantage: no new frequencies are needed, the signals are within the protected aviation range, and the infrastructure is already in development.
Cristallini explains: “ENAV has provided us with scenarios for the Italian airports in Perugia and Milan, where the LDACS-based passive radars are to be validated in the framework of the ASTONISH project. We are now examining whether we can cover these areas. Thanks to these simulations, we are getting a first impression of the suitability of LDACS as a reliable source for passive radar.”
The second development approach of ASTONISH is the aircraft-based alternative surveillance (A-SUR). The background: ADS-B (Automatic Dependent Surveillance-Broadcast), the currently leading flight tracking system, is increasingly facing limits due to spectrum overload in the 1090 MHz range and the susceptibility of GNSS (Global Navigation Satellite System) to interference. Therefore, ASTONISH is exploring how alternative data channels such as Satcom, LDACS, VDL-M2, 5G, and LTE can be utilized to securely and conformably transmit position data to ground stations.
The system design foresees redundant, encrypted, and authenticated data paths that can be operated in parallel with ADS-B. The architecture is compatible with existing ATM (Air Traffic Management) infrastructure, can be activated as needed, and creates additional redundancy in case of technical failures or targeted attacks on navigation and communication.
The third solution approach of the project focuses on sensors for ground operations, utilizing insights from the automotive sector. Therefore, ASTONISH relies on sensor fusion from camera, radar, and LiDAR technologies to precisely monitor aircraft movements during taxiing, parking, or in complex airport layouts—even under poor visibility conditions. It is clear on airport taxiways how important robust assistance systems are for the personnel involved. The challenge lies in integrating various sensor sources, each with its own strengths—from high-resolution optics to weather-resistant radar and accurate 3D mapping with LiDAR.
Outlook: Validation and Integration into Digital Airspace
By August 2026, ASTONISH will develop several demonstrators up to technology readiness levels TRL 2. Simulations at selected scenarios will demonstrate the extent to which the LDACS-based passive radar is suitable for airspace surveillance.
“We are in close contact with DLR, which has developed the LDACS standard,” explains Cristallini. “Through our expertise and reputation in passive radar, ENAV specifically approached Fraunhofer FHR as a partner.”
In the long term, ASTONISH is also intended to contribute to the implementation of the European ATM Master Plan and the "Digital European Sky" initiative. The project pursues a modern understanding of CNS (Communication, Navigation, Surveillance) based on automation, networking, and resilience—not as a stopgap solution, but as a robust future architecture for European air traffic management.