| dc.description.abstract | Single-photon time-of-flight (ToF) distance ranging lidar is a candidate technology for high-resolution depth imaging for use, for example, from airborne platforms. This approach enables low average power pulsed laser sources to be used while allowing imaging from significantly longer target ranges compared to analogue imaging. The recent availability of Geiger-mode (Gm) arrays has revolutionised photon-counting lidar as they provide single-photon full-frame data in short acquisition times.
This thesis presents work on the opto-mechanical design, tolerance analysis and performance evaluation of a re-configurable single-photon counting lidar which can accommodate either a single-element single-photon avalanche photodiode (SPAD) or a 32 × 32 Gm-array. By incorporating an inter-changeable lens, the two configurations were designed to provide identical pixel resolution for both the single-pixel system and the Gm-array configurations in order to permit a performance comparison to be conducted. This is the first time that such a comparison has been reported and the lidar is one of the earliest to assess the performance of a short-wave infra-red (SWIR) Gm-array. Both detection configurations used InGaAs/InP SPAD detectors and operated at a wavelength of 1550 nm. The main benefits of operating within the SWIR band include reduced solar background, lower atmospheric loss, improved covertness, as well as improved laser eye-safety thresholds. The system estimates target range by measuring the ToF using time-correlated single-photon counting (TCSPC) and was used to produce high-resolution three-dimensional images of targets at between 800 m and 10.5 km range. The single-element system has the potential to provide improved depth resolution over the array due to a smaller timing jitter but requires longer acquisition times due to the need for two-dimensional scanning. The acquisition time of the array configuration can be up to three orders of magnitude faster than the single-element configuration but requires significantly higher average laser power levels.
The Gm-array provided a simultaneous estimation of angle-of-arrival and intensity fluctuations from which a comparable strength of atmospheric turbulence could be measured. This demonstrated that Gm-arrays provide a new way of high-speed turbulence measurement with time intervals much shorter than those offered by existing scintillometers. | en_US |
