KEYWORDS: Target detection, Photon counting, Detection and tracking algorithms, Signal to noise ratio, LIDAR, Time correlated single photon counting, Clutter, Tunable filters, Pulse signals, Mirrors
Ultra-long-distance range-finding is often affected by scattering noise, resulting in a low Signal-to-Noise Ratio (SNR) due to the extremely weak retro-reflected light. Due to the low SNR, it is difficult to determine the corresponding distance from the sensor during the final stage of signal processing. It is challenging to adjust the threshold to achieve both a high detection rate and a low false alarm rate. In this study, we propose an effective detector for locating low SNR targets in ultra-long-distance measurements. The detector is based on the Constant False Alarm Rate (CFAR) processing framework widely used in radar target detection. We applied this detector for signal processing in the photon counting system for long-range, small dynamic targets, which we reported in our earlier work. In-site experiments were conducted in Dunhuang, Gansu in September 2021. We successfully performed long-range laser ranging for 60km buildings and ultra-long-range laser ranging for 152km mountain. The results showed that the proposed CFAR detector could quickly and efficiently extract target locations that were difficult to detect using a detector based on constant thresholding.
We proposed a long-distance underwater wireless optical communication with a single photon-counting system in a laboratory environment by using non-return to zero on-off keying modulation. The system successfully achieved a data rate of 1Mbps through a 15m PVC tube by adding in 80dB attenuator and using a pigtailed fiber 450nm blue laser diode. The water channel was measured to have an attenuation coefficient comparable to clean seawater. The experimental results show that under condition of only average 1.2 photons in single optical pulse, photon counting UOWC with a BER of 1. 6×10−4 and a baud rate of 1 Mbps can be achieved. Based on the measured minimum required power in the water channel, the transmission performance was predicted to be 140m and 310m in the clean seawater and pure seawater, respectively.
The time-of-flight method is widely used to measure the range of the targets directly. As the retro-reflected light is so weak in ultra-long-distance measurement, the measurement technique based on the single-photon detector (SPD) and the time-correlated single-photon counting (TCSPC) has been engaged in earth-satellite measurements and altimetry measurements for airborne platforms. But this technique is difficult to applied to dynamic target measuring, especially when the target is moving fast under significant background noise. In this paper, we develop a photon counting system for long-range small dynamic target such as aircraft. This system is based on a dynamic TCSPC method based on point-line duality which has been reported in our early work. Outdoor experiments were conducted to evaluate the ranging ability of our system. The experimental results that the laser ranging system can detect the moving Quadrotor UAV 3.6km away (emission optical attenuation 42.2dB) and the building 21km away (emission optical attenuation 26dB). Through equivalent calculation, it is equivalent to the range measurement of aircraft over 60km. Meanwhile, the photon-counting range finding system could measure the range and velocity of the small target such as moving Quadrotor UAV simultaneously. In addition, all the measurements of our range finding system was in real time.
This paper introduces a small object detection method based on 3D CNN in multispectral serial images. The temporal dimension is set as 5, which means the convolutional filter is n*n*c*5, because 5 consecutive images are sufficient to remove noises. We proposed a method for corresponding training sample preparation, where the true small object region is calculated and object moving in every direction is simulated which is called object simulation base region. The negative sample set is composed of random multispectral images while the positive sample set is composed by linear superposition of object simulation base regions. Experimental results proved this method is feasible and effective.
Underwater imaging always suffers strong absorption and scattering of water, leading to unsatisfactory imaging quality. Among these factors, scattering is considered as the main factor that makes underwater imaging fuzzy. Various methods have been introduced to eliminate the influence of scattering, and play a positive role in image enhancement, such as rangegated imaging, active polarization imaging and synchronous scanning technology. However, these methods appear limited effects in a higher level of turbidity conditions as it is generally believed that the multiple scattering photons are ascendant in a higher level of turbidity. In this paper, a new underwater image enhancing method was proposed. This method combined the tail-gating technology and the active polarization imaging technology. A range-gated imaging system was upgraded for verifying the novel method by adding polarizer in the light source unit and polarization analyzer in the light collecting unit. Experiments were conducted in a water tank size of 3m×0.6m×0.6m (L × W × H) that filled with running water is to simulate sea water condition in laboratory condition. The turbidly of sea water condition was simulated by adding Magnesium Hydroxide as scattered particles. Several groups of experiments under different range-gate setting and polarization strategy were conducted for comparison. The enhancement of the underwater imaging resolution was evaluated by computing the MTF (Modulation Transfer Function) values. The results said that the method combined the tail-gating and active polarization technology was capable of improving the imaging resolution in turbid underwater environment.
Single-photon LiDAR offers single-photon sensitivity and picoseconds timing resolution, leading to high-resolution images. In this paper, we investigate the reconstruction of depth and intensity profiles from data acquired using a custom designed time-of-flight scanning transceiver based on the time-correlated single-photon counting LiDAR. The system comprises a pulsed laser source at 1064nm wavelength, a monostatic scanning transceiver and a Si single-photon detector. The experimental result is present for reconstruction of high resolution depth and intensity profiles of targets obscured by camouflage at a distance of 425m in daylight. A total variation restoration optimization algorithm is performed to restore profiles of targets, and the results show that it maintains image quality for multi-depth targets while reducing acquisition times.
Compared with traditional Lidar, photon counting laser radar uses a high repetition rate and low pulse energy detection mechanism. The efficiency of laser echo can be improved by more than two orders of magnitude compared with traditional Lidar systems benefitting from the use of extremely sensitive Gm-APD (Geiger mode avalanche photodiode), which greatly improves the detection probability of the system. However, it becomes difficult to detect fast-moving targets within a long counting time, especially under the interference of high background noise. In order to detect high background, long distance and fast moving targets, we propose a dynamic TCSPC method based on point-line duality. The proposed method clusters the point clouds with a certain relationship in the original point cloud space, and finds the corresponding points in the parameter space that can connect some point clouds in a certain analytical form. Simulation results show that highspeed moving target can be detected.
In this paper, a far-field pseudo-thermal correlation imaging system is proposed which is mainly composed of laser, thermal field modulation system, speckle far field emission system and high-sensitivity intensity fluctuation detection system, etc.. Because the correlation imaging system is based on the principle of intensity fluctuation statistical measurement, it needs to be reconstructed after multiple measurements. An image reconstruction algorithm based on compressive sensing is applied in this paper, which makes full use of sparsity constraints to effectively improve the image restoration effect. Finally, the feasibility of the method is verified by actual imaging test. The experimental results show that the proposed system can clearly image the remote target and obtain better recovery images under the same sampling times.
KEYWORDS: 3D image processing, 3D acquisition, LIDAR, Single photon, Single photon detectors, Sensors, Superconductors, Nanowires, Imaging systems, Mirrors
Single-photon LiDAR offers single-photon sensitivity and picoseconds timing resolution, leading to high-resolution three-dimensional (3D) images. In this paper, we investigate the reconstruction of 3D images from data acquired using a custom designed time-of-flight scanning transceiver based on the time-correlated single-photon counting LiDAR. The system comprises a pulsed laser source at 1064nm wavelength, a monostatic scanning transceiver and a superconducting nanowire single-photon detector. The maximum distance of ranging finding under the experimental environments is up to 95.1km, and high-resolution 3D image of a pavilion is reconstructed at the range of 2.9km. A total variation restoration optimization algorithm is performed to reduce the acquisition time of the entire 3D images. Experimental results show that this system is feasible for imaging at longer range by refining the setup, and have potential for target recognition.
A division of aperture medium wave infrared Stokes imaging polarimeter (ISIP) with optimal linear polarization measurements is presented. The focal plane array of the ISIP is divided into four independent imaging channels by a lens array, which is turned into four independent polarimetric analyzing channels by placing four linear polarizers of different orientation angles in front of each channel and a wave plate in one of the channels. The experiments are performed for detecting camouflaged targets by using the optimized ISIP, which demonstrate that the polarimetric images are effective in detecting camouflaged targets form natural background and improving the signal to noise ratio of target images.
A division of aperture infrared Stokes imaging polarimeter (ISIP) with optimal linear polarization measurements is presented. The focal plane array of the ISIP is divided into four independent imaging channels by a lens array, which is turned into four independent polarimetric analyzing channels by placing four linear polarizers of different orientation angles in front of each channel and a wave plate in one of the channels. An optimization method for the four polarization analyzing channels is proposed to improve measurement accuracy. For a high priority to linear polarization measurement, instead of optimization for full states of polarization components, we optimize the ISIP first for linear polarization components and then for circular polarization component. We demonstrate that the orientation angles of the polarizers are set at 0°, 60°, 90° and 120°, respectively. The optimal retardance of the wave plate is 90° with the orientation angle of 0°.
The dual rotating-compensator Mueller matrix ellipsometer based on the optical configuration PC1r(ω1)SC2r(ω2)A has been developed recently with many applications such as characterization of thin film growth and surface modification. In this paper, the optimal configuration of this ellipsometer is performed by minimizing the condition number of the systematic data reduction matrix. We present the optimal orientation angles of the polarizer (P) and the analyzer (A), as well as the optimal number of sampling points and the optimal retardance of both compensators, and find that these optimal configurations at different frequency ratios of the two compensators (C1r and C2r) yield almost equal performance. Simulations conducted on this ellipsometer with different parameters have demonstrated that the optimal configuration improves the measurement accuracy.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.