Real-time imaging of moving targets through atmospheric obscurant using time-correlated single-photon counting

In recent years, there has been increasing interest in the use of Light Detection and Ranging (LiDAR) systems for measuring targets through visually degraded environments where man-made and natural obscurants such as smoke, fog, and haze can hinder the acquisition of high-resolution images. Single-photon time-of-flight LiDAR systems which employ the time correlated single photon counting (TCSPC) technique have emerged as a candidate technology for imaging in challenging environments due to the high sensitivity, excellent surface-to-surface resolution, and picosecond temporal resolution afforded by this approach. The time-of-flight LIDAR technique measures the round-trip time of flight of back-scattered photons, which when combined with optical scanning or use of multiple detectors, can obtain a three-dimensional profile of a target. These systems offer high resolution depth profiling in challenging measurement scenarios, for example at kilometre ranges and in turbid underwater environments, whilst maintaining low average optical power levels. In this work we present a bistatic single photon LiDAR system, designed for free-space imaging in highly attenuating environments, comprised of a picosecond pulsed fibre laser source at an operating wavelength of 1.55 µm and a 32 × 32 pixel format InGaAs/InP single photon avalanche diode (SPAD) detector array. This system, in conjunction with a newly developed advanced image processing algorithm, was used to obtain depth images of stationary targets, and three-dimensional videos of moving objects in real time, through high levels of atmospheric obscurants. We present analysis of the depth profiling of targets measured in obscurants corresponding to 5 attenuation lengths between transceiver at stand-off distances up to 150 metres and in high levels of solar background. The algorithm used in this analysis was designed for real time processing of sparse single photon data obtained in the presence of atmospheric obscurants and is well suited to scenarios with particularly high and non-uniform background levels such as observed when active imaging through obscurants.