We have developed a full-field solid-state range imaging system capable of capturing range and intensity data simultaneously for every pixel in a scene with sub-millimetre range precision. The system is based on indirect time-of-flight measurements by heterodyning intensity-modulated illumination with a gain modulation intensified digital video camera. Sub-millimetre precision to beyond 5 m and 2 mm precision out to 12 m has been achieved. In this paper, we describe the new sub-millimetre class range imaging system in detail, and review the important aspects that have been instrumental in achieving high precision ranging. We also present the results of performance characterization experiments and a method of resolving the range ambiguity problem associated with homodyne and heterodyne ranging systems.

No abstract

Abstract-Range imaging is a technology that utilizes an amplitude-modulated light source and gain-modulated image sensor to simultaneously produce distance and intensity data for all pixels of the sensor. The precision of such a system is, in part, dependent on the modulation frequency. There is typically a tradeoff between precision and maximum unambiguous range. Research has shown that, by taking two measurements at different modulation frequencies, the unambiguous range can be extended without compromising distance precision. In this paper, we present an efficient method for combining two distance measurements obtained using different modulation frequencies. The behavior of the method in the presence of noise has been investigated to determine the expected error rate. In addition, we make use of the signal amplitude to improve the precision of the combined distance measurement. Simulated results compare well to actual data obtained using a system based on the PMD19k range image sensor.Index Terms-Ambiguity, image sensor, range imaging, time of flight (ToF), 3-D camera.

Analysis of Langmuir probe characteristics contains a paradox in that it is unknown a priori which theory is applicable before it is applied. Often theories are assumed to be correct when certain criteria are met although they may not validate the approach used. We have analysed the Langmuir probe data from cylindrical double and single probes acquired from a dc discharge plasma over a wide variety of conditions. This discharge contains a dual-temperature distribution and hence fitting a theoretically generated curve is impractical. To determine the densities, an examination of the current theories was necessary. For the conditions where the probe radius is the same order of magnitude as the Debye length, the gradient expected for orbital-motion limited (OML) is approximately the same as the radial-motion gradients. An analysis of the 'gradients' from the radial-motion theory was able to resolve the differences from the OML gradient value of two. The method was also able to determine whether radial or OML theories applied without knowledge of the electron temperature, or separation of the ion and electron contributions. Only the value of the space potential is necessary to determine the applicable theory.

Abstract-The maximum unambiguous range for time-of-flight range imaging systems is inversely proportional to the chosen modulation frequency. However, increasing the unambiguous range by decreasing the modulation frequency will generally also degrade the range measurement precision. We describe a technique that significantly extends the range of a time-of-flight imaging system without compromising range precision. This is achieved by employing two modulation frequencies simultaneously. The chosen frequencies can be a combination of high and low frequency, or two similarly high frequencies.In this paper we present experimental results comparing single frequency; dual high and low frequency; and dual high frequency operation and demonstrate that range precision need not be appreciably compromised to achieve an extended unambiguous range.