A single-photon lidar ranging accuracy evaluation model

Single-photon Lidar (SPL) has many applications, ranging from geographic surveying to autonomous navigation. For accurate range extraction and range-walk-error (RWE) correction, a good TCSPC histogram is usually required and collected by using thousands of accumulations. While in high-flux regime, using a few accumulations is possible to perform range extraction and RWE correction and could speed up data acquisition process. This paper proposed a method to deal with two challenges of depth estimation when only a few accumulations (less than 10 times) are applied, including the extreme sparsity of photon-counting data and the non-steady state in free-running SPL. We first developed a forward model for non-steady state free-running SPL. As a second step, we computed the initial depth through our coarse depth estimation method, which incorporated the maximum of cross-correlation, threshold filtering, and cluster analysis of potential range candidates. Then solving an inverse problem through our forward model and initial values gives the estimate of the depth. Monte Carlo simulated results indicated good improvement in performance of detection probabilities and RWE correction. As compared with a baseline method, our method maintains a same detection probability while shows a 26% less false alarm probability on average. When signal-background ratio SBR is 0.2 (S = 2, B = 10) and accumulating times is only 4, our method gives a 75% less RWE. Our method could enable improvement of depth estimation from sparse photon-counting data collected by a few accumulations in SPL.

Detection of the near-field targets by non-coaxial underwater single-photon counting lidar

Moving target tracking in marine aerosol environment with single photon lidar system

Timing jitter as a key performance of single-photon avalanche diode (SPAD) detectors plays a significant role in determining the fast temporal response behavior of the SPAD device. Nevertheless, few analytic models are developed to directly calculate the characteristic of timing jitter for its modeling difficulty. In this paper, we propose a simple analytic modeling method, which can predict the temporal response of SPADs, without using time-consuming Monte Carlo simulation. Model investigation incorporates avalanche current, avalanche buildup time, and jitter tail under different conditions. Furthermore, the key model parameters provided by Geiger mode technology computer-aided design simulation allow an accurate prediction on timing jitter. Analytical results indicate that for an SPAD device structure with a shallow P+/N-well junction in a 0.18- $\mu \text{m}$ CMOS technology, the Gaussian peak response with about 110-ps full-width at half-maximum and the exponential jitter tail are in good agreement with the measured data, validating the accuracy, and feasibility of this modeling method.

Lidar has emerged as an important technology for the high-precision three-dimensional remote sensing of the ocean. While oceanic lidar has been widely deployed on various platforms, its underwater deployment is relatively limited, despite its significance in deep-sea exploration and obstacle avoidance for underwater platforms. Underwater lidar systems must meet stringent requirements for high performance, miniaturization, and high integration. Single-photon lidar, by elevating the detection sensitivity to the single-photon level, enables high-performance detection under the condition of a low-pulse-energy laser and a small-aperture telescope, making it a stronger candidate for underwater lidar applications. However, this imposes demanding requirements for the data acquisition system utilized in single-photon lidar systems. In this work, a self-developed multi-channel acquisition system (MCAS) with a high-resolution and real-time histogram statistics capability was developed. By utilizing field-programmable gate array (FPGA) technology, a method that combines coarse counters with multi-phase clock interpolation achieved an impressive resolution of 0.5 ns and enabled a time of flight duration of 1.5 μs. To address counting instability, a dual-counter structure was adopted in the coarse counter, and real-time histogram statistics were achieved in the data acquisition system through a state machine. Furthermore, the non-uniform phase shift of the clock was analyzed, and a correction algorithm based on code density statistics was proposed to mitigate the periodic modulation of the backscattered signal, with the effectiveness of the algorithm demonstrated through experimental results. The robustness and stability of the MCAS were validated through an underwater experiment. Ultimately, the development of this compact acquisition system enables the implementation of underwater single-photon lidar systems, which will play a crucial role in underwater target imaging, obstacle avoidance in underwater platforms, and deep-sea marine environment monitoring.

Timing jitter is a concern in high frequency oscillators; the presence of timing jitter will degrade system performance in many high speed applications. In the first part of the paper, the authors have simulated the timing jitter due to CMOS device noise in a nine-stage CMOS differential ring oscillator, and a methodology to efficiently simulate timing jitter has been developed. Simulation results show that the variation of absolute jitter due to flicker noise has t-dependence while for white noise it has t/sup 0.5/-dependence; these are consistent with accepted theory. Two important parameters, cycle jitter and cycle-to-cycle jitter, used to describe jitter performance can be obtained from simulation. Simulation results are also compared with measurement results, and it is shown that simulation results are very close to measurement results. All these serve to verify the validity of this technique. In the second part of the paper, the authors have employed this methodology and investigated the timing jitter in silicon BJT/or SiGe HBT ECL ring oscillators, and they have shown that BJT/or SiGe HBT oscillators have lower jitter compared to their CMOS counterparts. The methodology described in the paper is also applicable to other types of clock generator and oscillators such as LC oscillators, as well as other kinds of noise source such as power supply and substrate noise.

Single-photon lidar has emerged as a strong technology for bathymetric measurements. However, its heightened sensitivity additionally makes it susceptible to solar radiation noise, particularly in the green light wavelength where solar radiation is strong, posing challenges for its daytime operation. To address this issue, a single-photon underwater lidar system is proposed and demonstrated. This scheme has these features. 1) Underwater applications not only mitigate the impact of the air-water interface on laser transmission but also significantly attenuate solar radiation reaching the lidar due to the absorption and scattering properties of water. 2) The telescope is designed with a small aperture and narrow field of view to significantly suppress solar radiation. 3) A combination of a narrowband laser and narrowband filter technique is effectively employed to minimize residual solar radiation, thus enabling continuous bathymetric observation capabilities during both day and night. 4) After acquiring the backscattered signal from the bottom, a water depth extraction algorithm utilizing bi-Gaussian fitting is proposed. To demonstrate the robustness of the lidar and the effectiveness of the algorithm, the underwater single-photon lidar system is deployed on a ship to conduct cruise surveys of two bays in the nearshore area, as well as a full-day stationary observation experiment. The lidar measurements are highly consistent with the synchronized sonar observations. The full-day stationary observation experiment showcased its capability to deliver continuous measurements throughout the day and night. These results demonstrate the potential of the system in various applications, including high-precision underwater terrain mapping, obstacle avoidance for underwater platforms, and underwater target imaging.

Single-photon lidar (SPL100) is a recently commercialized airborne lidar system facilitating efficient wide-area acquisitions of high-density point clouds due to its capacity for higher altitude acquisitions compared to traditional linear-mode lidar (LML) systems. Increased acquisition efficiency and point densities make SPL100 attractive for forest management applications. SPL100 utilizes 532 nm (green wavelength) lasers, wherein there is reduced reflectance from vegetation, increased sensitivity to solar noise, and increased signal attenuation, which may impact the vertical distribution of SPL100 returns in forest canopies. We assessed SPL100 data acquisitions over managed forests in north-eastern Ontario, Canada, using high-density unmanned aerial vehicle-borne laser scanning (ULS) data as reference over a range of forest conditions with variable vertical structure. Signal attenuation depth of individual SPL100 returns was estimated through a surface model normalization approach stratified by a ULS-derived structural index that compared densities of returns in the upper canopy to low vegetation and near ground. Canopy signal attenuation was closely matched in both systems, particularly in the upper canopy and near the ground surface; however, results showed a 31% reduction in the relative characterization of mid-canopy vegetation layers by SPL100 under conditions identified by the structural index as closed canopy, compared to the ULS system.

Under the condition of the higher order effects, a propagation equation is established to investigate the way to suppress the soliton self frequency shift and timing jitter in the picosecond and femtosecond soliton communication system using a combined control method of time domain and frequency domain. By the use of the variational approach, the evolution of the chirping Gaussian quasi-soliton pulse is analyzed in the presence of the effects including third order dispersion, intrapulse Raman scattering (IRS), and self steepening. Considering the soliton evolution properties and the mechanism of the timing jitter under the higher-order effects, the combined control method is adopted to eliminate the influence from Raman scattering and self-steepening. The soliton central frequency is stabilized and the timing jitter is suppressed effectively. A 160 Gb/s long-haul soliton transmission system is designed and its performance is numerically simulated. The simulation results are in good agreement with our theoretical analysis.

Side-looking SAR cannot image targets in flight direction. Introduced here is the bistatic missile-borne forward-looking SAR system, as an efficient approach to forward-looking SAR imaging. According to the spatial geometry and the model of echo signal, the signal spectrum derived by the method of series reversion, the phase compensation factors and the realized step of the proposed algorithm are given. Several simulation and processing results are presented to demonstrate the validity of the proposed algorithm.

Satellite laser ranging (SLR), a cornerstone technology in space geodesy, plays a critical role in satellite orbit determination and Earth gravity field inversion. Here, we developed a compact single-photon LiDAR system for SLR operating at 1550 nm. The system features a bistatic configuration for backscattering noise suppression, an enhanced scan-tracking technique to improve dynamic target detection probability, and an absolute ranging method utilizing chaotic pulse position modulation (CPPM) and the Hough transform. Experimental results demonstrate a static target absolute ranging of 8.56 km, and dynamic ranging capabilities of up to 953.89 km with a ranging RMSE of 0.41 m. The theoretical normal point precision at high pulse repetition frequencies is estimated to be within a few millimeters. Trajectory and full-waveform analysis further validate the system's ability to detect radial velocity (-6.53 ∼ -2.05 km/s ) and attitude changes of targets. This work proves the feasibility of single-photon LiDAR for SLR applications and enables what we believe to be new solutions for satellite orbit determination, space target identification, attitude sensing and debris monitoring.

Marine remote target signal extraction based on 128 line-array single photon LiDAR

Synthetic Aperture Radar (SAR) is a coherent imaging radar. Hence, coherence is critical in SAR imaging. In a coherent system, several sources can degrade performance. Based on the HJ-1-C SAR system implementation and sensor characteristics, this study evaluates the effect of frequency stability and pulse-to-pulse timing jitter on the SAR coherent performance. A stable crystal oscillator with short-term stability of 101.010 / 5 msis used to generate the reference frequency by using a direct multiplier and divider. Azimuth ISLR degradation owing to the crystal oscillator phase noise is negligible. The standard deviation of the pulse-to-pulse timing jitter of HJ-1-C SAR is lower than 2ns (rms) and the azimuth random phase error in the synthetic aperture time slightly degrades the side lobe of the azimuth impulse response. The mathematical expressions and simulation results are presented and suggest that the coherent performance of the HJ-1-C SAR system meets the requirements of synthetic aperture radar imaging.

The chapter is dedicated to dynamic testing of Analog-to-Digital Converters (ADCs) by means of both time- and frequency-domain sine-fitting algorithms (SFAs). At first the sine-fitting procedure used for the estimation of SIgnal-to-Noise And Distortion ratio (SINAD) and Effective Number Of Bits (ENOB) parameters is described. In the following the expressions for the bias and the standard deviation of the ENOB estimator provided by a SFA are derived. Then, the SFAs based on the Interpolated Discrete Fourier Transform (IpDFT) method, the Energy-Based (EB) method, and the well known three- and four-parameter SFAs are separately analyzed. For each algorithm, the basic theoretical background and the operational detail are given. Moreover, the accuracy of all the presented algorithms are compared by means of both theoretical and simulation results. Some aspects concerning the influence of the harmonics, time jitter, and time base distortions on the dynamic performance of an ADC are also discussed. Besides, some Multi-Harmonics Sine-Fitting Algorithms (MHSFAs) are briefly described. Finally, the accuracy of the ENOB estimates provided by the considered SFAs and MHSFAs are compared through real-world data.

Investigation of the timing jitter generated by propagating high-power optical pulses through short lengths of optical fiber is presented. It is measured using the phase-encoded optical sampling technique. Comparisons are made between measured and simulated results.