- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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ObstacleWatch
摘要： Walking while using a smartphone is becoming a major pedestrian safety concern as people may unknowingly bump into various obstacles that could lead to severe injuries. In this paper, we propose ObstacleWatch, an acoustic-based obstacle collision detection system to improve the safety of pedestrians who are engaged in smartphone usage while walking. ObstacleWatch leverages the advanced audio hardware of the smartphone to sense the surrounding obstacles and infers fine-grained information about the frontal obstacle for collision detection. In particular, our system emits well-designed inaudible beep signals from the smartphone built-in speaker and listens to the reflections with the stereo recording of the smartphone. By analyzing the reflected signals received at two microphones, ObstacleWatch is able to extract fine-grained information of the frontal obstacle including the distance, angle and size for detecting the possible collisions and to alert users. Our experimental evaluation under two real-world environments with different types of phones and obstacles shows that ObstacleWatch achieves over 92% accuracy in predicting obstacle collisions with distance estimation errors at about 2 cm. Results also show that ObstacleWatch is robust to different sizes of objects and is compatible to different phone models with low energy consumption.
关键词： Smartphone,Acoustic Ranging,Mobile Sensing,Pedestrian Safety,Acoustic Localization
更新于2025-09-23 15:23:52
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[IEEE OCEANS 2018 MTS/IEEE Charleston - Charleston, SC, USA (2018.10.22-2018.10.25)] OCEANS 2018 MTS/IEEE Charleston - Developments and applications of underwater LiDAR systems in support of marine science
摘要： Light Detection and Ranging (LiDAR) has been used extensively to accumulate high-resolution topographical data in air. Over the last few decades, the technology has been extended to capture bathymetric data in coastal waters. With a large portion of the ocean unmapped, there is opportunity for technology advancement to deliver improved quality and efficiency in the mapping of shallow water regions. This paper assesses existing technology and the history of underwater LiDAR profiling and bathymetric mapping to identify potential opportunities for future growth. Alternative uses for laser ranging systems, both subsea and in-air will drive expected system specifications. The findings assist with classifying important design choices that drive the functionality and suitability of a LiDAR for different marine science applications.
关键词： ranging,SLAM,bathymetry,subsea,topography,lidar,underwater
更新于2025-09-23 15:22:29
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A correction method for range walk error in time-correlated single-photon counting using photomultiplier tube
摘要： Time-correlated single-photon counting (TCSPC) is one of the most active technologies for optical time-of-flight ranging and three-dimensional (3D) imaging. It has attracted much attention because of its high sensitivity, high ranging accuracy and excellent resolution. TCSPC is applicable for the cases of detecting weak signals, usually for the cases when the detection probability is not higher than 0.01 to 0.1 photons per signal period. However, the reflectivity of the targets to be measured varies greatly in practical applications. Usually the energy of the retuned signal from targets varies over two orders of magnitude. It is unrealistic to dynamically regulate the energy of the laser source at a high frequency to match the reflectivity of targets. A phenomenon of photon pile-up will occur in detecting strong signals, which will lead to a range walk error. The error is particular serious if the pulse width of the laser is relatively wide, such as a nanosecond laser which is extensively used in practical applications. Therefore, investigation of TCSPC under strong returned signal conditions has important significance to extend the application domains of the TCSPC lidar systems. In this paper, ranging accuracy under conditions of different signal intensities using PMT and one-stop TDC is focused on. The photon pile-up caused by the change of amplitude and distortion of reconstructed laser waveform are theoretically analyzed. A correction method for the range walk errors under strong signal situations is proposed and validated in a laser ranging experiment. The results show that, using the correction method, ranging errors can be reduced from 183 mm to 6 mm for the case when the average number of photon is 9.6. The applicable returned signal domain of the TCSPC technique is extended by two orders of magnitude compared to the conventional weak signals. The accuracy and flexibility of TCSPC ranging system will be greatly improved using the proposed error correction method under strong signal conditions.
关键词： Three-dimensional imaging,Lidar,Laser ranging,Photon counting
更新于2025-09-23 15:22:29
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Background Light Rejection in SPAD-Based LiDAR Sensors by Adaptive Photon Coincidence Detection
摘要： Light detection and ranging (LiDAR) systems based on silicon single-photon avalanche diodes (SPAD) offer several advantages, like the fabrication of system-on-chips with a co-integrated detector and dedicated electronics, as well as low cost and high durability due to well-established CMOS technology. On the other hand, silicon-based detectors suffer from high background light in outdoor applications, like advanced driver assistance systems or autonomous driving, due to the limited wavelength range in the infrared spectrum. In this paper we present a novel method based on the adaptive adjustment of photon coincidence detection to suppress the background light and simultaneously improve the dynamic range. A major disadvantage of fixed parameter coincidence detection is the increased dynamic range of the resulting event rate, allowing good measurement performance only at a specific target reflectance. To overcome this limitation we have implemented adaptive photon coincidence detection. In this technique the parameters of the photon coincidence detection are adjusted to the actual measured background light intensity, giving a reduction of the event rate dynamic range and allowing the perception of high dynamic scenes. We present a 192 × 2 pixel CMOS SPAD-based LiDAR sensor utilizing this technique and accompanying outdoor measurements showing the capability of it. In this sensor adaptive photon coincidence detection improves the dynamic range of the measureable target reflectance by over 40 dB.
关键词： system-on-chip (SoC),single-photon avalanche diode (SPAD),CMOS,light detection and ranging (LiDAR),time-of-flight (TOF),background light rejection
更新于2025-09-23 15:22:29
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Massively parallel coherent laser ranging using a soliton microcomb
摘要： Coherent ranging, also known as frequency-modulated continuous-wave (FMCW) laser-based light detection and ranging (lidar)1 is used for long-range three-dimensional distance and velocimetry in autonomous driving2,3. FMCW lidar maps distance to frequency4,5 using frequency-chirped waveforms and simultaneously measures the Doppler shift of the reflected laser light, similar to sonar or radar6,7 and coherent detection prevents interference from sunlight and other lidar systems. However, coherent ranging has a lower acquisition speed and requires precisely chirped8 and highly coherent5 laser sources, hindering widespread use of the lidar system and impeding parallelization, compared to modern time-of-flight ranging systems that use arrays of individual lasers. Here we demonstrate a massively parallel coherent lidar scheme using an ultra-low-loss photonic chip-based soliton microcomb9. By fast chirping of the pump laser in the soliton existence range10 of a microcomb with amplitudes of up to several gigahertz and a sweep rate of up to ten megahertz, a rapid frequency change occurs in the underlying carrier waveform of the soliton pulse stream, but the pulse-to-pulse repetition rate of the soliton pulse stream is retained. As a result, the chirp from a single narrow-linewidth pump laser is transferred to all spectral comb teeth of the soliton at once, thus enabling parallelism in the FMCW lidar. Using this approach we generate 30 distinct channels, demonstrating both parallel distance and velocity measurements at an equivalent rate of three megapixels per second, with the potential to improve sampling rates beyond 150 megapixels per second and to increase the image refresh rate of the FMCW lidar by up to two orders of magnitude without deterioration of eye safety. This approach, when combined with photonic phase arrays11 based on nanophotonic gratings12, provides a technological basis for compact, massively parallel and ultrahigh-frame-rate coherent lidar systems.
关键词： photonic chip,FMCW lidar,soliton microcomb,parallel distance and velocity measurements,coherent ranging
更新于2025-09-23 15:21:01
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A Novel Topology for Process Variation-Tolerant Piezoelectric Micromachined Ultrasonic Transducers
摘要： This paper presents a novel architecture for piezoelectric micromachined ultrasonic transducers (PMUT) allowing for a drastic reduction in the impact of process variations on the accuracy of the resonant frequency. At the core of this new topology is a toroidal anchoring technique. Measurement results show that inter- and intra-die resonant frequency standard variations can be reduced from 101 kHz to 23 kHz and from 20 kHz to 5.9 kHz, respectively, by using the method proposed in this paper, showcasing devices fabricated using the PiezoMUMPs commercial fabrication technology. From the 16 chips that have been fabricated, each holding 12 PMUT devices of two different topologies, resonant frequency results are presented and analyzed to assess the effectiveness of the proposed approach. In addition, as a proof of concept, the fabricated PMUT are demonstrated to perform distance ranging measurements.
关键词： frequency,ranging measurements,variability,process variation,MEMS,PMUT,Piezoelectric ultrasonic transducers,microfabrication
更新于2025-09-23 15:21:01
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A Local Projection-Based Approach to Individual Tree Detection and 3-D Crown Delineation in Multistoried Coniferous Forests Using High-Density Airborne LiDAR Data
摘要： Accurate crown detection and delineation of dominant and subdominant trees are crucial for accurate inventorying of forests at the individual tree level. The state-of-the-art tree detection and crown delineation methods have good performance mostly with dominant trees, whereas exhibits a reduced accuracy when dealing with subdominant trees. In this paper, we propose a novel approach to accurately detect and delineate both the dominant and subdominant tree crowns in conifer-dominated multistoried forests using small footprint high-density airborne Light Detection and Ranging data. Here, 3-D candidate cloud segments delineated using a canopy height model segmentation technique are projected onto a novel 3-D space where both the dominant and subdominant tree crowns can be accurately detected and delineated. Tree crowns are detected using 2-D features derived from the projected data. The delineation of the crown is performed at the voxel level with the help of both the 2-D features and 3-D texture information derived from the cloud segment. The texture information is modeled by using 3-D Gray Level Co-occurrence Matrix. The performance evaluation was done on a set of six circular plots for which reference data are available. The high detection and delineation accuracies obtained over the state of the art prove the performance of the proposed method.
关键词： forest,3-D tree crown delineation,tree top detection,airborne laser scanner,Light Detection and Ranging (LiDAR)
更新于2025-09-23 15:21:01
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Application and Validation of a Model for Terrain Slope Estimation Using Space-Borne LiDAR Waveform Data
摘要： The terrain slope is one of the most important surface characteristics for quantifying the Earth surface processes. Space-borne LiDAR sensors have produced high-accuracy and large-area terrain measurement within the footprint. However, rigorous procedures are required to accurately estimate the terrain slope especially within the large footprint since the estimated slope is likely affected by footprint size, shape, orientation, and terrain aspect. Therefore, based on multiple available datasets, we explored the performance of a proposed terrain slope estimation model over several study sites and various footprint shapes. The terrain slopes were derived from the ICESAT/GLAS waveform data by the proposed method and five other methods in this study. Compared with five other methods, the proposed method considered the influence of footprint shape, orientation, and terrain aspect on the terrain slope estimation. Validation against the airborne LiDAR measurements showed that the proposed method performed better than five other methods (R2 = 0.829, increased by ~0.07, RMSE = 3.596?, reduced by ~0.6?, n = 858). In addition, more statistics indicated that the proposed method significantly improved the terrain slope estimation accuracy in high-relief region (RMSE = 5.180?, reduced by ~1.8?, n = 218) or in the footprint with a great eccentricity (RMSE = 3.421?, reduced by ~1.1?, n = 313). Therefore, from these experiments, we concluded that this terrain slope estimation approach was beneficial for different terrains and various footprint shapes in practice and the improvement of estimated accuracy was distinctly related with the terrain slope and footprint eccentricity.
关键词： terrain slope,Geoscience Laser Altimeter System (GLAS),estimation accuracy,footprint diameter,Light Detection and Ranging (LiDAR)
更新于2025-09-23 15:21:01
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Observation of topologically enabled unidirectional guided resonances
摘要： Unidirectional radiation is important for various optoelectronic applications, such as lasers, grating couplers and optical antennas. However, almost all existing unidirectional emitters rely on the use of materials or structures that forbid outgoing waves—that is, mirrors, which are often bulky, lossy and difficult to fabricate. Here we theoretically propose and experimentally demonstrate a class of resonances in photonic crystal slabs that radiate only towards one side of the slab, with no mirror placed on the other side. These resonances, which we name ‘unidirectional guided resonances’, are found to be topological in nature: they emerge when a pair of half-integer topological charges in the polarization field bounce into each other in momentum space. We experimentally demonstrate unidirectional guided resonances in the telecommunication regime by achieving single-side radiative quality factors as high as 1.6 × 105. We further demonstrate their topological nature through far-field polarimetry measurements. Our work represents a characteristic example of applying topological principles to control optical fields and could lead to energy-efficient grating couplers and antennas for light detection and ranging.
关键词： Unidirectional radiation,Light detection and ranging,Photonic crystal slabs,Telecommunication regime,Grating couplers,Topological charges
更新于2025-09-23 15:19:57
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Multilayer Thermal Model for Evaluating the Performances of Monofacial and Bifacial Photovoltaic Modules
摘要： This paper gives a detailed description of prelaunch and in-orbit calibrations of the Mercury Laser Altimeter (MLA) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, which was launched on August 3, 2004 and has been operating in orbit about Mercury since March 2011. A brief summary of the MLA instrument is given, followed by the instrument measurement model and calibration formulas. The prelaunch tests used to determine the values of various calibration coefficients are described. The boresight alignment parameters were verified and recalibrated by special tests, with the MESSENGER spacecraft en route to Mercury. The MLA instrument model and the calibration methods were largely derived from airborne and spaceborne lidar for Earth science observation at the NASA Goddard Space Flight Center and will benefit future space lidar developments for Earth and space science.
关键词： Laser ranging,lidar
更新于2025-09-23 15:19:57