KEYWORDS: LIDAR, Stereoscopy, Reconstruction algorithms, Imaging systems, Detection and tracking algorithms, Time correlated single photon counting, Single photon detectors, Sensing systems, Active imaging, Statistical analysis
Laser 3D imaging system has a very wide range of applications, such as satellite remote sensing and airborne surveillance. With the development of single photon detection technology, 3D imaging system based on single photon detection can meet these demanding requirements. In particular, single-photon detectors can provide single-photon sensitivity and ultra-high temporal resolution, and this high sensitivity allows the use of lower power lasers with longer detection distances. In this paper we present an active imaging system based on the single-photon ToF approach to obtain depth profiles of targets. The bistatic system comprised a pulsed laser source with an operational wavelength of 1064nm and an InGaAs/InP SPAD detector array which is highly efficient in the SWIR region.
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.
Lidar is a promising active imaging technology that utilizes laser as the signal source to obtain accurate range, azimuth, speed, and other target characteristics, enabling 3D scene perception. Single photon lidar, using high sensitivity single photon detectors and high-frequency photon counting, has greatly improved the detection range of lidar. However, achieving large field of view and high resolution in single-photon 3D imaging remains a challenge. Therefore, we propose a long-distance single photon 3D imaging lidar based on dual wedge scanning, where the dual wedge scanning method is employed to extend the field of view, and the GM-APD array is utilized to improve imaging speed. In this work, we investigate the distribution characteristics of the point cloud in dual wedge scanning and propose a sub-pixel scanning-based 3D reconstruction and image processing method for point cloud. Through our approach, we successfully achieve large field of view, high resolution, and fast 3D imaging. Our method can be applied in a wide range of applications, including investigation, mapping, unmanned driving, and more.
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.
As a new type of active imaging technology, single photon counting 3D imaging has great application value in the fields of biophotonic imaging, remote sensing mapping, weak target detection, etc. Generally, in order to mitigate the influence of noise photons during the detection, it is necessary to accumulate hundreds of photons per pixel to form a histogram of arrival photons to obtain an accurate 3D image. However, in conditions of low illumination or long distances targets detecting, the available echo energy and the allowable integration time generally do not satisfy the collection of such large number of photons. Therefore, we research on single photon 3D imaging method based on a few echo photons, and several image reconstruction algorithm under strong background noise environment was proposed, including traditional methods based on pixels as well as newly proposed methods based on spatial correlation. We use the 3D point cloud signal to achieve the 3D reconstruction of the target reflectivity signal and distance information.
Dynamic laser speckle or biospeckle has become an important tool to investigate biological activity. Now, we present a method to study the viability of seed using dynamic laser speckle in frequency domain. Compared with other traditional method such as Fujii, our method has been demonstrated to be more accurate and we can evaluate the level of seed viability. The results obtained in experiment on both lived and died seeds are shown as examples
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