20. A non-transitory computer-readable medium comprising computer-executable instructions for unattended detection of a current terrain to be traversed by a mobile device, the instructions configured to: receive visual input, from a visual sensor, of the current terrain for a plurality of positions; receive audio input corresponding to the current terrain for the plurality of positions; fuse the video input with the audio input using a classifier; and classify the type of the current terrain with the classifier.
21. The computer-readable medium of claim 20 , wherein the classifier is constructed using an expectation-maximization (EM) method.