Resolving range ambiguity in a photon counting depth imager operating at kilometer distances

Abstract

Time-correlated single-photon counting techniques have recently been used in ranging and depth imaging systems that are based on time-of-flight measurements. These systems transmit low average power pulsed laser signals and measure the scattered return photons. The use of periodic laser pulses means that absolute ranges can only be measured unambiguously at low repetition rates (typically <100 kHz for > 1 km) to ensure that only one pulse is in transit at any instant. We demonstrate the application of a pseudo-random pattern matching technique to a scanning rangefinder system using GHz base clock rates, permitting the acquisition of unambiguous, three-dimensional images at average pulse rates equivalent to >10 MHz. Depth images with centimeter distance uncertainty at ranges between 50 m and 4.4 km are presented.

Time-correlated single-photon counting range profiling and reflectance tomographic imaging

“…The inherent feature of photon counting and low laser power emission makes TCSPC covert, in particular considering the possibility to use sparse waveforms and pseudo-random pulse streams. One example in this respect is absolute range finding [16,45]. Other critical issues related to the performance of the method include whether the studied objects can be considered to be stationary in relation to the integration time.…”

“…The scanning in the lateral plane was accomplished using a pair of galvanic mirrors. A method to overcome the range ambiguity problem in TCSPC imaging was presented showing centimetre range accuracy at 50 m and 4.4 km [16]. Krichel et al also proposed a novel method for generation of 3D data utilising a cumulative acquisition approach building up depth information from several lateral frames [17].…”

Optimization of eyesafe avalanche photodiode lidar for automobile safety and autonomous navigation systems

“…11,12 The ambiguity determines the maximum laser repetition rate-and, ultimately, the peak laser power and average laser power-and is, thus, an important system-design parameter. As shown in Table 1, the unambiguous laser-repetition rate, for 220-m range returns is 682 kHz-a rate that is 528× less than the ∼360-MHz rate required to sample the 360-deg × 20-deg FOR with the specified resolution and update rate.…”

Time-Correlated Single-Photon Counting Range Profiling of Moving Objects

“…The absolute distance to an object can be determined e.g. by using pseudo-random modulation of the laser pulse train [3,4], but that feature is not implemented in the current set-up.…”