Sonar

What is Sonar?

Sonar (Sound Navigation and Ranging) is a technique that uses sound waves to detect and measure distances to objects. In robotics, sonar sensors (often ultrasonic sensors) are commonly used for short-range obstacle detection and distance measurement.

How Sonar Works

A sonar sensor emits a high-frequency sound pulse and listens for its echo after it bounces off an object. The time between emission and reception is used to calculate the distance:

Distance = (Time × Speed of Sound) / 2

The division by 2 accounts for the round trip of the sound wave.

Types of Sonar in Robotics

1. Ultrasonic Rangefinders

Common in hobby and educational robots. Low cost, simple interface, limited to 2–4 meters.

2. Multibeam Sonar

Used in underwater robotics (AUVs/ROVs) for mapping large areas. Provides multiple beams for detailed imaging.

3. Imaging Sonar

Produces sonar images like radar, used in murky or dark underwater environments where cameras fail.

Applications of Sonar in Robotics

1. Obstacle Detection

Sonar sensors are used to detect nearby walls, objects, or people to prevent collisions.

2. Autonomous Navigation

Mobile robots and drones can use sonar to sense surroundings in GPS-denied or low-light areas.

3. Underwater Exploration

Sonar is crucial for underwater robots, where optical sensors are ineffective due to turbidity and lack of light.

4. Level Sensing and Object Detection

Sonar can be used to measure liquid levels or detect objects in storage bins and tanks.

Advantages

  • Low cost and easy to integrate
  • Works in complete darkness
  • Effective on flat and reflective surfaces
  • Safe and non-intrusive (uses sound, not light)

Limitations

  • Limited range and resolution
  • Affected by environmental noise
  • Inaccurate on soft or angled surfaces
  • Slower update rate compared to LiDAR

Sonar Integration in ROS

In ROS, sonar data is typically published using sensor_msgs/Range. Drivers and packages include:

  • rosserial_arduino for microcontroller-based sonar
  • hector_sensors_description for integrating sonar with mobile robots

Visualization is done in rviz, and sonar data can be fused with IMU and odometry for navigation.

Conclusion

Sonar remains a valuable sensing modality in robotics, especially where cost, safety, and simplicity are priorities. Although limited in resolution compared to LiDAR or cameras, sonar provides robust short-range detection and is indispensable in underwater and low-light environments.