On ultrasonic detection of surface features

Ultrasonic range finding is an inexpensive means of obtaining 3-dimensional information about the surrounding environment. Because of this ultrasonic detection methods have received considerable attention recently, particularly in the robotic community. Unfortunately, ultrasonic range finding suffers from shortcomings that are not found in more expensive techniques such as laser range finding. For example, a laser range finder can determine both range from the sensor and location of the reflection surface due to the narrow beam used. The ultrasonic range finder beam is much larger and reflection surface location can only be determined approximately for any single range sample (it is only known that a reflecting surface lies somewhere on a segment of the surface of a sphere of range radius centered on the sensor). This paper discusses techniques for obtaining much better surface information under certain conditions. These techniques form the foundation for more sophisticated methods described in another paper for extracting surface features. The techniques can be used with other range sensors and look particularly promising for adaptively controlling a laser range finder. We will outline the mathematical techniques employed and discuss some experience obtained with a robot mounted ultrasonic range sensor.