| Whereas in the past ultrasonic
sensors have been largely used only to estimate the proximity of objects
and the location and identification of primitive targets in a robot workspace,
the development of biomimetic sonar has opened up new possibilities for
their application. Broadband sonar echoes have sufficient resolution so
that characteristics on reflection, especially geometry and texture, can
be distinguished with only a few measurements. In this paper, we describe
how a model of texture can be used to distinguish between a number of different
surfaces using only a single measurement of each, showing results on a number
of surfaces that might be considered typical pathways for a mobile robot,
both those with periodicity in pattern and those with statistically homogeneous
features. In particular, we consider textures corresponding to hard smooth
floors, carpets and asphalts, and surfaces with a repeating pattern made
up of tiles. Each rough surface class is modeled using an extension of the
Kirchhoff approximation method describing the scattering of the acoustic
wave on the surface while the periodic ones are modeled assuming distinctive
reflections from the tile borders. The continuous transmission frequency-modulated
sonar signature corresponding to each class is derived and compared with
the experimental one. A set of features is extracted that exploits the differences
between the surface models, and a hierarchical classification scheme is
proposed for recognition. |
