1 March 1992 Comparison of continuous-wave and pulsed time-of-flight laser range-finding techniques
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Time-of-flight laser rangefinders based on the propagation speed of light and direct detection may be roughly divided into two classes depending on whether their light emission is continuous or pulsed. In the modulated continuous wave (CW) rangefinding technique an amplitude modulated light carrier is emitted and the distance information is extracted from the received signal by comparing its modulation phase to that of the emitted signal. In the pulsed time-of-flight (TOF) rangefinding method the distance is obtained by measuring the time interval between the transmitted and received light pulses. A comparison is made in this paper between the TOF and CW techniques in terms of the range measurement resolution achievable. The basis for comparison is that the actual measurement or averaging time is the same with both techniques. Comparison is made in the case where the average optical power level used is the same and also in that in which an unambiguous measurement distance is set for both techniques. With an equal average optical power level and a noise contribution dominated by the signal itself, it is shown that the ratio of achievable range resolution between the TOF and CW techniques is directly proportional to the ratio of the modulation frequency of the CW method to the receiver bandwidth of the TOF method. When the average optical power level is reduced and the photon-noise limited condition is not achieved, the TOF mode rangefinder gains an advantage over the CW mode because the resolution is directly proportional to the optical power level and the available energy in the TOF technique can be concentrated at the moment of timing. This enables a TOF rangefinder to be much faster than a similar CW rangefinder in many practical applications.
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Markku Koskinen, Markku Koskinen, Juha Tapio Kostamovaara, Juha Tapio Kostamovaara, Risto A. Myllylae, Risto A. Myllylae, } "Comparison of continuous-wave and pulsed time-of-flight laser range-finding techniques", Proc. SPIE 1614, Optics, Illumination, and Image Sensing for Machine Vision VI, (1 March 1992); doi: 10.1117/12.57989; https://doi.org/10.1117/12.57989

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