Four Natural Technical Barriers to Under-Bridge Inspection
The bottom of a bridge is the core area with the highest structural hazards, the hardest to inspect, and the most prone to long-term neglect. It naturally involves multiple harsh working conditions and represents a common industry technical bottleneck.
Weak Satellite Signals
Beam concrete and steel structures fully block satellite signals from the sky. Under-bridge areas are generally in GPS/BeiDou signal-free or weak-signal states, making conventional drones unable to position.
Completely Satellite-Free Environment
Enclosed box girders, deep beam bottoms and densely packed bearing areas are completely beyond GNSS satellite coverage, causing traditional positioning systems to fail entirely.
Extremely Complex Structures
Internal diaphragms, bearings, prestressed structures and pipelines are densely packed, with narrow spaces and intersecting structures that easily cause collisions.
Extremely Low Clearance
Some municipal bridges, ramp bridges and box-girder bridges have narrow under-bridge clearances with very little room for error, making manual control extremely difficult.
Why Ordinary Drones Cannot Complete Under-Bridge Inspection
The vast majority of commercial drones on the market rely entirely on satellite positioning for flight. Once they enter the under-bridge environment, they directly experience positioning loss, drift, unstable hovering, and attitude control failure.
Positioning Failure Blocks Autonomous Flight
No satellite signal means no positioning coordinates. The system cannot plan routes or lock positions, and fully automatic inspection comes to a direct halt.
Extremely High Flight Drift Risk
Relying on inertial navigation easily causes position drift. Even a slight offset can collide with beam bottoms, diaphragms or bearings, creating a very high crash risk.
Blind Manual Flying Only, No Standardization
Traditional solutions can only rely on pilots visually flying blind under bridges, heavily dependent on individual experience with no fixed routes, no repeatable operations, and no comparable data.
Long-Term Blind Spots Left Behind
Most inspection units can only inspect the deck and outer sides of piers. Under-bridge defects remain undetected for long periods, creating maintenance safety hazards.
Cannot Adapt to AI Standardized Inspection
Without stable positioning, there are no unified shooting angles or trajectories, making it impossible to match the data standards of digital twin modeling and AI defect detection.
Self-Developed Multi-Source Fusion Visual Navigation, Completely Free of Satellite Dependence
Riejian breaks through the industry's general dependence on satellite navigation with self-developed vision + multi-sensor fusion positioning technology, achieving stable, precise and autonomous under-bridge flight in zero-satellite environments. This is the core underlying technology for full-bridge automatic inspection.
Visual Navigation Core
Relies on real-time matching of bridge scene structural features for positioning, independent of any satellite signal, using the environmental structure as the positioning reference and adapting to all enclosed under-bridge scenarios.
Multi-Sensor Fusion
Integrates vision, inertial measurement, ranging and other multidimensional data to compensate for single-navigation shortcomings, with strong anti-interference capability and stability far exceeding traditional solutions.
Centimeter-Level Position Calculation
Outputs high-precision position and attitude data in real time, precisely locking the drone's spatial coordinates and preventing flight drift or offset.
Fully Autonomous Unmanned Flight
After positioning is stabilized, preset routes are executed automatically with no manual control, adapting to routine, standardized, reusable inspection operations.
Closed-Loop Fully Automatic Inspection Workflow in Satellite-Free Environments
Leveraging Riejian's under-bridge navigation capability, we build a blind-spot operation system with data standards fully unified with deck inspection, achieving unmanned operations, standardized data, comparable results and full hazard coverage to fill the gap in under-bridge inspection.
Adapting to Blind-Spot Inspection of Mainstream Complex Bridge Types
Box Girder Bridge Scenarios
For enclosed single-box and multi-box girder interiors with narrow, dark, densely structured and completely satellite-free conditions, enables full interior traversal inspection, precisely identifying fine cracks and spalling on top slabs, webs and bottom slabs.
Cable-Stayed Bridge Scenarios
Adapted to wide beam bottoms, dense stay cables and complex anchorage zones of long-span cable-stayed bridges, stably completing large-area beam-bottom full-coverage inspection while avoiding cable interference to ensure no high-risk areas are missed.
Suspension Bridge Scenarios
For the long-span, low-altitude and flexible deck structures of suspension bridges, enables long-distance continuous autonomous flight, adapting to slight vibrations in flexible structures to ensure stable trajectories and unified data standards.
Steel Structure Bridge Scenarios
Adapted to complex steel box girder and steel truss structures, targeting high-frequency defects such as steel corrosion, weld cracking and loose bolts, with stable positioning and precise collection within dense steel frames to solve steel under-bridge inspection challenges.
Four Core Advantages of Under-Bridge Autonomous Navigation
True Full-Area Coverage
Fills the biggest blind spot of traditional inspection, achieving 100% coverage of deck, piers, towers, bearings, beam bottoms and box girder interiors for inspection without dead zones.
Highly Standardized Operations
Removes dependence on pilot experience. Under-bridge routes can be fixed, reused and compared, unified with the deck inspection data system to support long-term defect trend analysis.
Greatly Improved Operational Safety
Fully automatic flight in low-clearance, enclosed and dangerous areas eliminates the need for close-range manual control, completely avoiding high-altitude and under-bridge operational safety risks.
Deployment on Mega Bridges
An essential underlying capability for digital inspection of super-large bridges such as river-crossing, sea-crossing and large interchange bridges, supporting compliant acceptance of major projects.
Frequently Asked Questions
Detailed answers to core questions about GPS-free under-bridge autonomous navigation.
RIEJIAN's self-developed under-bridge autonomous navigation module seamlessly switches with GPS, achieving centimeter-level positioning in GPS-denied under-bridge environments to inspect girder soffits, bearings and other areas.
No. The system adapts to low-light, dark and complex-occlusion scenarios. Trained on massive real-scene samples of box girders and bridge undersides, it adapts to the extreme operating environments of dark, structurally dense and texture-complex under-bridge areas, with stable, drift-free positioning.
Yes. The under-bridge navigation capability works closely with the digital twin base and intelligent route planning. Routes planned after first-time modeling can be permanently solidified and reused; each flight's trajectory, shooting angle and collection scope are completely identical, enabling precise multi-period comparison of under-bridge defects and tracking defect development trends.
Drones are not used inside box girders. Instead, a crawler robot enters the box cavity for internal inspection, while the drone covers exterior structures such as the girder soffit. The combination of the two achieves full coverage of the box girder structure.
Yes. The fully automatic under-bridge imagery matches AI defect detection and 3D modeling requirements in clarity, overlap and shooting standards. After engineer review, it can be directly included in standardized inspection and periodic inspection reports, meeting industry acceptance and archiving requirements.
The essential difference: ordinary drones only have simple obstacle avoidance, with no positioning capability and no route-reproduction capability; RIEJIAN's under-bridge navigation is a complete underlying navigation system of "positioning + computation + route execution + stable hovering" — the core technology enabling standardized, reusable, comparable under-bridge inspection.
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