The useful environmental interaction of a mobile robot is completely dependent on the reliable extraction of information from its immediate surroundings. A review of some of the most commonly used coaxial, active sensing methods in robotics is presented. A coaxial sensor results if the transmitter and receiver are geometrically arranged in a coaxial manner. Certain advantages of such configurations are discussed. First, optical sensors, in which a controlled light signal is transmitted, are reviewed with respect to their applicability to mobile robotics research. A detailed overview of the literature describing light detection and ranging (LIDAR) systems for range measurement in robotics is given. In any LIDAR design, the physics of reflection of light from various surfaces must be addressed. Specular and/or diffuse reflection results which greatly affects a sensor's ability to measure range. The issues of the type of reflection, dynamic range of the received signal strength, and crosstalk are addressed in relation to three popular LIDAR measurement techniques-time of flight and frequency/amplitude modulated continuous wave methods. A review of mobile robot research using sound navigation and ranging (SONAR) is presented where processing algorithms are demonstrated for the correct interpretation of ultrasonic data recorded in indoor environments. Once again, to understand the data provided by ultrasonic sensors, a model of the reflection mechanism is required. Ultrasonic wave reflection is generally dominated by specular reflections. Methods for the interpretation of SONAR data, for correct target classification, and, hence, range estimation are given, based on the acoustic reflection mechanism. This requires SONAR scans of particular objects from multiple view points. Recent research has focussed on the use of arrays of SONARS to eliminate the necessity for multiple view point scanning, for the classification of targets. Methods will be presented which adopt multiple SONAR transducers to allow target identification and range estimation from a single view point. Where possible, actual sensor data is presented to highlight the review.
