Understanding Sensor Fusion: Combining Sensors to See More Clearly


What is Sensor Fusion?
Sensor fusion is the process of integrating multiple sensor inputs to provide enhanced awareness of the environment and activities. By combing different types of sensors, a more complete and accurate understanding can be obtained compared to using only a single sensor. Sensor fusion allows autonomy systems to perceive the world in a more similar way as humans.

Multimodal Perception
One approach to sensor fusion involves using multiple sensing modalities together, such as cameras, LiDAR, radar, ultrasonics and infrared. Cameras provide a wealth of visual information like color, texture and shapes, but cannot measure distances. LiDAR uses lasers to accurately detect depth but lacks visual characteristics. Integrating camera imagery with 3D point clouds from LiDAR creates a rich multimodal understanding. Radar detects objects at long ranges in all weather conditions but with lower resolution compared to cameras/LiDAR. Fusing radar data with vision sensors adds a complementary sensing capability. Combining different types of sensors in this way results in a perception system that is more robust and reliable than any single sensor alone.

Temporal Fusion
Temporal fusion uses sensor data collected over time to track objects and understand dynamic events. By correlating detections from successive time steps, the trajectories and motions of objects can be inferred even if they are temporarily occluded from one sensor’s view. Previous observations about an object’s location, speed and heading help predict where it will be in the next time step. Sensor fusion over time disambiguates noisy measurements and resolves uncertainties, leading to more consistent tracking of objects as they move through the environment. For autonomous vehicles, temporal fusion is essential for perceiving other road users like cars and predicting their future behavior.

Multi-sensor Object Tracking
Tracking identifiable objects across different sensors over time is an important application of sensor fusion. Visual features extracted from camera imagery can be associated with 3D detections from LiDAR point clouds to link objects between the two sensing domains. By maintaining distinct tracks for individual objects, their 6DoF poses and semantic classifications can be continuously estimated even when visibility varies between sensors. For example, a car may be visible to a camera but temporarily blocked from LiDAR by another vehicle. Associating measurements to the same tracked object model enables robust perception during brief occlusions or failures in any single sensor. Complex datasets from multiple synchronized sensors can be simultaneously processed to derive a unified world model.

Sensor Complementarity
Effectively fusing data from complementary sensors leads to more complete scene understanding compared to any single sensor in isolation. For instance, cameras provide abundant visual features but lack depth perception whereas LiDAR precisely measures 3D geometry but not visual properties like texture. By combining camera images with LiDAR point clouds, both the “what” (object appearance from cameras) and “where” (object position from LiDAR) can be inferred. Radar too has a complimentary role, as it can detect objects obscured from optical cameras/LiDAR by detecting their reflections. Fusing information from these various sensing modalities synergistically combines their respective strengths while compensating for individual weaknesses or limitations. This results in perceptions systems with wider fields of view, longer ranges, better accuracy and reliability compared to any single sensor technology.

Future Directions
As sensor and compute capabilities continue advancing, new opportunities are emerging for more sophisticated fusion techniques. Deeper neural network models are allowing raw sensor data streams to be fused at the pixel-level before semantic interpretation. Multi-modal networks can learn joint representations directly from raw sensor inputs like images and point clouds without extensive preprocessing. Feature extraction and fusion is performed simultaneously through end-to-end deep learning. Advanced SLAM (simultaneous localization and mapping) techniques fuse inertial, visual and depth data to build consistent metric maps in real-time. Sensor models are also being integrated with prediction and decision making for closed loop perception-action. As autonomous systems deploy broader sensor suites, more nuanced sensor fusion algorithms will be crucial to realize their full perception potential. The future of robot perception lies in synergistically combining all available sensory inputs.

In summary, sensor fusion techniques integrate data from multiple sensors to provide enhanced environmental awareness compared to a single sensor alone. By combining complementary sensing modalities, a more complete model of the world can be perceieved that accounts for each sensor’s strengths and limitations. As autonomous machines equip richer sensor arrays, sensor fusion will become increasingly important to realize reliable perception in complex, real world conditions. Proper integration of diverse sensor inputs through advanced algorithms is key to building truly perceptive artificial intelligence.



  1. Source: Coherent Market Insights, Public sources, Desk research
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