I. INTRODUCTION
This paper discusses a simple approach to terrain identification, based on the exploitation of contact dynamics. Surface sensing using a feeler can have several advantages for navigation. In the simplest case, the feeler can be used to detect anomalous surface conditions such as holes in the ground. More interestingly, it can be used to probe terrain properties. These properties, for example visco-elasticity or friction, might be challenging to measure accurately using vision or laser range-finders.