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I. Background Overview

With the proliferation of unmanned aerial vehicle (UAV) technology, which plays a positive role in areas such as aerial photography, inspection, and logistics, it also introduces security risks such as "low-altitude intrusion" and "illegal flight". At critical sites like airports, military installations, energy infrastructure, and key industrial parks, traditional monitoring methods—such as radar, video, or radio frequency surveillance—still have certain limitations when dealing with low-altitude, stealthy, and small-target scenarios.

Distributed Acoustic Sensing (DAS) systems, as a passive, long-range, continuous-monitoring sensing technology, offer a new technical approach for UAV intrusion early warning.

II. Fundamental Principles of DAS in UAV Intrusion Monitoring

DAS systems leverage the Coherent Optical Time-Domain Reflectometry (C-OTDR) principle, transforming standard telecommunications optical fiber into a continuous, distributed array of vibration and acoustic sensing units along its length. When a UAV performs low-altitude flight, takeoff/landing, or hovering in a target area, it generates detectable physical disturbances in the ground and surrounding structures, including:

• Micro-vibrations in the ground induced by rotor downwash.

• Impact and resonance during UAV takeoff and landing.

• Distinctive acoustic wave signatures produced by low-altitude flight.

These signals are transmitted via the optical fiber to the DAS interrogation unit. Through high-speed data acquisition and digital signal processing, real-time sensing and precise localization can be achieved.

III. DAS Monitoring Modes for UAV Intrusion Scenarios

1. Perimeter and Key Area Low-Altitude Intrusion Monitoring

In areas such as airport perimeters, military restricted zones, substations, and along oil/gas pipelines, optical fiber can be deployed along fences, underground, or within existing conduits.
When a UAV enters the monitored zone, the DAS system can:

• Real-time detection of anomalous vibrations and acoustic signatures.

• Localize the UAV activity zone along the fiber length.

• Temporally and spatially log intrusion events.

Compared to video surveillance, DAS is independent of lighting conditions and has no field-of-view blind spots.

2. UAV Takeoff and Landing Behavior Recognition

Illegal UAVs often need to execute takeoff or landing maneuvers near the target area.
DAS is particularly sensitive to such scenarios, enabling the following through analysis of signal characteristics:

• Identification of takeoff/landing vibration patterns.

• Capture of short-duration, high-energy acoustic-vibration signals.

• Effective discrimination from other events like personnel walking or vehicle movement.

This capability is highly valuable for scenarios involving "rapid takeoff – short-duration reconnaissance – swift撤离 (withdrawal)".

3. Integrated Application with Counter-UAS Systems

DAS itself does not actively emit any signals, offering high covertness. It can serve as the front-end sensing layer for Counter-Unmanned Aircraft Systems (C-UAS):

• DAS provides early passive warning.

• It guides radar, electro-optical, or UAV jamming/disruption systems for directional tracking.

• Reduces the workload and false alarm rate of active detection systems.

Through multi-system integration, the overall reliability of the C-UAS can be significantly enhanced.

IV. Technical Advantages of DAS in UAV Intrusion Monitoring

1. Passive Monitoring, Secure and Covert
   The system generates no electromagnetic emissions, making it suitable for deployment in high-security scenarios.

2. Long-Range, Continuous Coverage
   A single system can achieve continuous sensing over tens of kilometers, suitable for large-scale protected areas.

3. High Spatial Localization Accuracy
   Meter-level positioning capability provides precise coordinate information for subsequent response actions.

4. Strong Resilience to Complex Environments
   Unaffected by factors such as rain, fog, darkness, or electromagnetic interference.

5. Algorithms Can Be Optimized for UAV Signatures
   Through spectral analysis, time-frequency feature extraction, and pattern recognition, a UAV signature database can be progressively built, improving identification accuracy.

V. Engineering Implementation and System Capabilities

In practical engineering applications, DAS systems typically require high sampling rates, high dynamic range, and real-time processing capabilities to adapt to the rapidly changing characteristics of UAV-related signals.

Taking the Distributed Acoustic Sensing system provided by Shanghai Kunlian Technology as an example, its hardware platform and algorithmic architecture are optimized for high-frequency vibration and weak signal detection. It can meet the requirements for continuous monitoring and real-time analysis in complex scenarios, providing a stable data foundation for UAV intrusion awareness.

VI. Development Trends and Outlook

With the increasing demand for low-altitude security, single detection methods are insufficient to meet the requirements of complex scenarios.
In the future, DAS will be more deeply integrated with:

• Radar systems

• Electro-optical identification systems

• AI-powered intelligent analysis platforms

forming a comprehensive counter-UAV solution characterized by "passive sensing + active identification + intelligent decision-making".

Within this framework, DAS will continue to play a stable and reliable role as a fundamental sensing layer, providing solid support for low-altitude security protection.

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