Introduction

Humans have long been interested in devices which extend their senses, the telescope being an early example of such a device. We have since progressed to systems which operate in domains beyond the normal senses, as in the use of x-rays in medical imaging or seismic waves to probe the earth. Nevertheless, most existing remote sensing systems operate with considerable human input and interpretation; naturally, there is great interest in developing remote sensing systems which can with greater autonomy identify or recognize salient aspects of their environments. Potential applications of such systems abound:

1. Air-traffic control (identification of incoming aircraft).

2. Air defense (recognizing friendly or hostile aircraft).

3. Quality assurance (assembly line inspection).

4. Medical screening (identifying anomalies in radiographic or tomographic images).

5. Security and surveillance systems.

6. Robotics (navigation, carrying out tasks).

7. Exploration geophysics (interpreting seismic data).

8. Analytical chemistry (neutron activation analysis, nuclear magnetic resonance, other kinds of spectroscopy).

9. Detection of unexploded subsurface munitions.

All of these systems have in common the detection and processing of signals. In some cases (e.g., radar), the system must also emit a signal which interacts with the environment and is subsequently detected in modified form.

Though our understanding of human perception and information processing is incomplete, the very fact that recognition and identification are biologically possible demonstrates that the problem is not fundamentally intractable.