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Target geolocation using UAVs is crucial for search and rescue missions. A method based on laser trilateration using the EO/IR pod on a UAV is proposed, with no deed for accurate camera orientation and reference maps that methods like aerial triangulation require. The target geolocation model is established using least square optimization, with additional steps to reduce errors, including 1) atmospheric refraction correction; 2) Earth Centered Earth Fixed (ECEF) frame usage to avoid length distortion introduced by map projection. Experimental validation at 15,000 m distance shows a 5.8 m geolocation error, offering a reliable and efficient alternative to existing methods. [ABSTRACT FROM AUTHOR]

Abstract Mount Rainier has had at least 11 large lahars over the last 6,000 years, including one occurring without evidence of eruptive activity. This prompted the creation of a lahar detection system that uses a combination of seismic, infrasound, and tripwires. We test a laser rangefinder placed on a river channel bank for detecting and confirming mass movements flowing past a station as an alternative to the physical tripwires. After testing the device at an experimental debris-flow flume, the laser rangefinder successfully captured a small debris flow on Mount Rainier in 2023, confirming its effectiveness as a lahar detection and monitoring tool. Over the 2-month deployment at Mount Rainier, we find that spurious recordings in the laser rangefinder data (noise) tend to correlate with high humidity, and that periods of noise do not correlate with increased co-located seismic amplitude. Therefore, the impact of the noise on future alarms can be mitigated by coupling a laser rangefinder alarm with that of independent datasets.

The paper provides a detailed treatment of the expected range performance for the laser rangefinder (LRF) developed for the Polish ImAging SaTellites (PIAST) space mission, where the distance between satellites within a constellation has to be measured during orbital flight. The satellites are equipped with corner cube retroreflectors (CCR) to increase the efficiency of laser back-reflection. A theoretical signal-to-noise range-dependence model was developed to determine the maximum expected range of the measurements. This model included the tilt-angle-dependent properties of the CCR far-field diffraction patterns (FFDP) which were measured experimentally. In addition, the specific parameters of the receiving optoelectronic circuit used were considered. The obtained results show that in the case of the constructed PIAST LRF (peak laser pulse power of 100 W, laser beam divergence of 5 mrad, receiving optical aperture diameter of 2 in, CCR diameter of 2 in), depending on the CCR angular inclination, a maximum measurement distance of 15-40 km is expected. [ABSTRACT FROM AUTHOR]

Currently, for underwater close-range large-target localization, visual localization techniques fail since large targets completely occupy the camera's field of view at ultraclose ranges. To address the issue, a multi-stage optical localization method combining a binocular camera and a single-point laser rangefinder is proposed in this paper. The proposed method comprises three parts. First, the imaging model of the underwater camera is modified, and a laser rangefinder is used to further correct the underwater calibration results of the binocular camera. Second, YOLOv8 is applied to recognize the targets to prepare for target localization. Third, extrinsic calibration of the binocular camera and laser rangefinder is performed, and a Kalman filter is employed to fuse the target position information measured by the binocular camera and laser rangefinder. The experimental results show that, compared with using a binocular camera alone, the proposed method can accurately and stably locate the target at close ranges with an average error of only 2.27 cm, without the risk of localization failure, and reduces binocular localization error by 90.57%. [ABSTRACT FROM AUTHOR]

The safety enhancement of small fixed-wing UAVs regarding obstacle detection is addressed using optimization techniques to find the best sensor orientations of different multi-sensor configurations. Four types of sensors for obstacle detection are modeled, namely an ultrasonic sensor, laser rangefinder, LIDAR, and RADAR, using specifications from commercially available models. The simulation environment developed includes collision avoidance with the Potential Fields method. An optimization study is conducted using a genetic algorithm that identifies the best sensor sets and respective orientations relative to the UAV longitudinal axis for the highest obstacle avoidance success rate. The UAV performance is found to be critical for the solutions found, and its speed is considered in the range of 5–15 m/s with a turning rate limited to 45°/s. Forty collision scenarios with both stationary and moving obstacles are randomly generated. Among the combinations of the sensors studied, 12 sensor sets are presented. The ultrasonic sensors prove to be inadequate due to their very limited range, while the laser rangefinders benefit from extended range but have a narrow field of view. In contrast, LIDAR and RADAR emerge as promising options with significant ranges and wide field of views. The best configurations involve a front-facing LIDAR complemented with two laser rangefinders oriented at ±10° or two RADARs oriented at ±28°. [ABSTRACT FROM AUTHOR]

The safety enhancement of small fixed-wing UAVs regarding obstacle detection is addressed using optimization techniques to find the best sensor orientations of different multi-sensor configurations. Four types of sensors for obstacle detection are modeled, namely an ultrasonic sensor, laser rangefinder, LIDAR, and RADAR, using specifications from commercially available models. The simulation environment developed includes collision avoidance with the Potential Fields method. An optimization study is conducted using a genetic algorithm that identifies the best sensor sets and respective orientations relative to the UAV longitudinal axis for the highest obstacle avoidance success rate. The UAV performance is found to be critical for the solutions found, and its speed is considered in the range of 5–15 m/s with a turning rate limited to 45°/s. Forty collision scenarios with both stationary and moving obstacles are randomly generated. Among the combinations of the sensors studied, 12 sensor sets are presented. The ultrasonic sensors prove to be inadequate due to their very limited range, while the laser rangefinders benefit from extended range but have a narrow field of view. In contrast, LIDAR and RADAR emerge as promising options with significant ranges and wide field of views. The best configurations involve a front-facing LIDAR complemented with two laser rangefinders oriented at ±10° or two RADARs oriented at ±28°.

A unique rangefinder that, as far as we know, was not mentioned in previous publications has been studied. It is based on an injection diode laser with an eye-safe radiation density (below 1 μJ/cm2) and a single-photon avalanche diode (SPAD). A new lasing mode of the nanosecond laser with a 200-ps-long step at the leading edge of a 4-ns-long pulse with spatial extension of about 1.2 m has been implemented. It has been found that the discovered step of the optical pulse amplitude is initiated by a current avalanche in a field-effect transistor (FET) that switches capacitance discharge in the feed circuit of the diode laser. The detection of the 200-ps-long amplitude step by a quick-response SPAD detector (20 ns) improves the accuracy of the rangefinder by 12 times. The application of such rang finder to measure critical distances (shorter than the laser pulse extension), e.g., in the problems of space ship landing or docking and underwater robot rendezvous and approach has been discussed. [ABSTRACT FROM AUTHOR]

An instrument and technique for assessing errors of measuring optical surface radius of curvature with a laser rangefinder are presented. Errors of optical instrument alignment with a wave-front sensor are shown to influence the accuracy of measuring the mirror radius. Errors of the rangefinder-aided technique for measuring the surface radius are estimated. A computer analysis shows that the developed scheme of misalignment measurement allows a relative error of 0.02 – 0.3 % to be attained for mirrors ranging in radius from 1 m to 10 m. The choice of the accuracy characteristics of the rangefinders used for measuring the optical surface radius of curvature is justified.

A prototype of a pulsed diode-pumped laser based on Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) crystal emitting at 1064 nm is presented for use in airborne rangefinders and atmospheric LIDARs without use of expensive production technologies and components.Actively Q-Switched laser pulse energy was estimated. Spatial characteristics of laser beam and dependence of pulse energy on the pump pulse energy were obtained at room temperature. Results of diodepumped laser pulse energy measurements are provided within 2 min for pulse repetition rates of 1, 4, 12.5, 22 Hz at ambient temperature range from -40 to +60 °C. Laser diode arrays temperature stabilization was achieved by the use of Peltier module with cooling capacity of 30 W.Pulse energy values not less than 80 mJ were achieved in the studied ranges of ambient temperature and pulse repetition rate. Laser beam divergence at room temperature does not exceed 1.9 mrad.

Currently, for underwater close-range large-target localization, visual localization techniques fail since large targets completely occupy the camera’s field of view at ultraclose ranges. To address the issue, a multi-stage optical localization method combining a binocular camera and a single-point laser rangefinder is proposed in this paper. The proposed method comprises three parts. First, the imaging model of the underwater camera is modified, and a laser rangefinder is used to further correct the underwater calibration results of the binocular camera. Second, YOLOv8 is applied to recognize the targets to prepare for target localization. Third, extrinsic calibration of the binocular camera and laser rangefinder is performed, and a Kalman filter is employed to fuse the target position information measured by the binocular camera and laser rangefinder. The experimental results show that, compared with using a binocular camera alone, the proposed method can accurately and stably locate the target at close ranges with an average error of only 2.27 cm, without the risk of localization failure, and reduces binocular localization error by 90.57%.

Satellite photogrammetry is an important way to obtain geospatial information of the earth, and it is also an effective way to solve the mapping issue for difficult areas in the world. The development process of optical surveying and mapping satellites are briefly summarized, and the optical surveying and mapping satellites of China are introduced in detail. After years of technological development, the results of optical photogrammetry satellites in China can meet the accuracy requirements of 1∶50 000 and 1∶10 000 scale surveying and mapping products. And the development status of optical surveying and mapping satellites are summarized, and the future development trends of surveying and mapping satellites are proposed, including on-board intelligent detection and storage, on-board and ground data intelligent processing, and multi-satellite network collaborative detection. With the support of global high-precision basic information data, the future photogrammetry satellites will be developed in the direction of an integrated, ubiquitous and intelligent type to improve the guarantee capability of surveying and mapping products. [ABSTRACT FROM AUTHOR]

Sweetness or sugar content, represented by soluble solids contents (SSC), is a vital quality trait in watermelon breeding which can be assessed by the refractive index method. However, sampling watermelon juice out of the pulp is a process that is both labor-intensive and error-prone. In this study, we developed an automatic SSC measurement system for watermelon breeding to improve efficiency and decrease costs. First, we built an automatic cutting system to cut watermelons into precise halves, in which a laser rangefinder is used to measure the distance from the upper surface of the watermelon to itself, and thus, the diameter is estimated. The experiments showed a high correlation between the estimated diameters and the ground truths, with R 2   =   0.9608 and RMSE   =   4.321 . Then, we built an automatic Brix measurement system to obtain the Brix data from a central point on the watermelon's section, where an image analysis procedure is applied to locate the testing point. This is then transformed to the camera coordination system, and a refractometer is driven by a 3-axis robotic arm to reach the testing point. Brix measurement experiments were conducted using three vertical gaps and four lateral gaps between the probe of the refractometer and the pulp. The result showed that the best parameters were a vertical gap of 4 mm and a lateral gap of 2 mm. The average accuracy reached 98.74%, which indicates that this study has the potential to support watermelon breeding research. [ABSTRACT FROM AUTHOR]

A new method providing for formation of the power of pulses within the required range of laser rangefinders is given. For this, a special device for illuminating the input lens of the installation is used. [ABSTRACT FROM AUTHOR]

We present the design and experimental characterization of a CMOS sensor based on Single-Photon Avalanche Diodes for direct Time-Of-Flight single-point distance ranging, under high background illumination for short-range applications. The sensing area has a rectangular shape ( $40\,\,\mathbf {\mathrm {\times }}\,\,10$ SPADs) to deal with the backscattered light spot displacement across the detector, dependent on target distance, due to the non-confocal optical setup. Since only few SPADs are illuminated by the laser spot, we implemented a smart laser-spot tracking within the active area, so to define the specific Region-Of-Interest (ROI) with only SPADs hit by signal photons and a smart sharing of the timing electronics, so to significantly improve Signal-to-Noise Ratio (SNR) of TOF measurements and to reduce overall chip area and power consumption. The timing electronics consists of 80 Time-to-Digital Converter (TDC) shared among the 400 SPADs with a self-reconfigurable routing, which dynamically connects the SPADs within the ROI to the available TDCs. The latter have 78 ps resolution and 20 ns Full-Scale Range (FSR), i.e., up to 2 m maximum distance range. An on-chip histogram builder block accumulates TDC conversions so to provide the final TOF histogram. We achieve a precision better than 2.3 mm at 1 m distance and 80% target reflectivity, with 3 klux halogen lamp background illumination and 2 kHz measurement rate. The sensor rejects 10 klux of background light, still with a precision better than 20 mm at 2 m.

High-power lasers have severe thermal effects. The heat buildup during long-term operation will increase the threshold current of the laser and the internal defects, which will seriously affect the lifetime of the device. A temperature sensor is difficult to install on the laser rangefinder due to the small size of the solid-state laser device. Considering this situation, this work analyses the thermal mechanism of the laser rangefinder and proposes a temperature calculation method for the crystal working substance inside the laser rangefinder based on the finite element simulation to obtain the crystal center temperature and thermal model with the working time. Then, the prediction model of the maximum continuous working time of the laser can be obtained. The proposed model can provide an early scientific warning for the remaining continuous working time of the solid-state laser and improve the single-shot utilization of the solid-state laser to a certain extent. A comprehensive health management framework of laser rangefinders including FMEA is also proposed. [ABSTRACT FROM AUTHOR]

The article presents results of research on the influence of changes in parameters of the digitally recorded echo signals on the uncertainty of pulsed Time-of-Flight (p-ToF) laser distance measurements. The main objective of the study was to evaluate the distance calculation method developed by the authors. This method is based on the acquisition of the full-waveform of the echo pulse signal and approximation of its shape by the second-degree polynomial (we called it SDPA for short). To determine the pulse transit time and measure the distance, the position of the vertex of this parabola is sought. This position represents the maximum intensity of the incoming echo signal and is related to the round-trip propagation time of the laser pulse. In the presented work, measurement uncertainty was evaluated using simulation tests for various parameters of the echo pulse. All obtained results were used to formulate the general relationship between the measurement uncertainty of the SDPA algorithm and the parameters of the received echo signals. This formula extends the base knowledge in the domain of laser p-ToF distance measurements. It can be used to estimate the measurement uncertainty of a FW LiDAR at an early design stage. This greatly improves capabilities of analysis of expected performance of the device. It can also be implemented directly into the rangefinder's measurement algorithm to estimate the measurement uncertainty based on the emission of a single pulse rather than a series of pulses. [ABSTRACT FROM AUTHOR]

In order to meet the demand of the mine robot powered by battery for self fast and safe charging in the mine, a charging method of mutual conversion between electric energy and mechanical energy in the mine is proposed. This paper designs an autonomous and fast charging system for coal mine robot, which is composed of robot, walking track, guiding mechanism and charging station. The robot drives to the charging station independently along the walking track under the guidance of the guiding mechanism. The accurate and reliable docking between the robot and the charging station is ensured by the rotary encoder and laser rangefinder. The safety of charging docking is ensured by the flame retardant and antistatic modified nylon butt joint male and female. After successful docking, the motor of the charging station drives the generator of the robot to charge the battery of the robot with high power and fast speed. After successful docking, the motor of the charging station drives the generator of the robot to charge the battery of the robot with high power and fast speed. The test results show that the stable output power of the generator is more than 800 W when the rated power of the motor is 2.2 kW, which provides a new method for autonomous fast and safe charging of coal mine robot.

The acceptance of binding and rebar installation is the last and vital step in construction engineering. However, there are many environmental constraints in the acceptance of the quality of rebar binding, which affect the acceptance. To address these problems, this study proposes an image-based intelligent distance measurement system, proving convenient for workers to measure long distances. The solution could effectively improve the measurement range during the acceptance process of rebar binding. The proposed method is divided into three steps. In the first step, a laser rangefinder was employed to measure the distance between the camera and the rebar; in the second step, the corner detector, based on the improved Harris corner detection algorithm, was used to detect the corners of the rebar images; and in the third step, the value of laser distance measured and the pixel value obtained by the corner detector was adopted for distance measurement. The method our proposed has a positive impact on the quality acceptance process of rebar binding, which can greatly improve the acceptance efficiency and save time. [ABSTRACT FROM AUTHOR]

Pines (genus Pinus) are cultivated extensively for forestry purposes, particularly in regions that are outside the genus' native range. The most common forestry species are also typically those most likely to escape cultivation and spread rapidly, and thus pines constitute a substantial weed problem in many regions. However, there is limited knowledge of the factors underlying the spread of pines from plantations. Assessments across heterogeneous landscapes are required to provide rigorous data to support management tools and policies aiming to protect vulnerable ecosystems from pine invasions.We examined the spread of Pinus radiata from forestry plantations over a ~9,000 km2 landscape on Banks Peninsula, New Zealand. We used ground‐based surveys from a set of viewpoints to determine tree locations, coupled with geographical information system (GIS) viewsheds to define the area surveyed. We used boosted regression trees to build a habitat model for P. radiata establishment on Banks Peninsula.We surveyed an area approximately 107 km2, recording 470 naturally established P. radiata individuals. Our habitat models suggested that proximity to the nearest plantation forest was the most important variable predicting P. radiata establishment, with individuals most likely to establish within 150 m of a plantation. Individuals were also most likely to establish in early successional shrub communities, proximate to roads, and on steeper topography. Highly grazed habitats were least vulnerable to P. radiata establishment.The slope and aspect of the source plantation influenced the distances from the plantation at which P. radiata individuals were recorded, with individuals recorded furthest away likely to have originated from plantations that were south‐facing or on steeper slopes, and therefore most exposed to strong winds.Synthesis and applications. Our findings on distances from plantations at which individuals established, vulnerable habitats, and the interactions we detected among our predictor variables, can be extended to aid management of non‐native conifer plantings elsewhere in the Southern Hemisphere. These data can be used to contribute to improvements of decision support systems that assess likely spread risk from non‐native conifer plantings. Such tools can reduce the likelihood of future pine establishment, potentially preventing biological invasions. [ABSTRACT FROM AUTHOR]

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A target tracking system with a laser rangefinder is developed, and the performance of the developed system is verified by a numerical simulation and field tests. To develop the target tracking system, appropriate coordinate systems, motion models, and estimation methods are selected, and a range filter is designed to compensate for the measurement errors of the laser rangefinder. The range filter independently processes the range measurements so that the target filter continuously produces the target information. The entire target tracking system development process is described in detail to facilitate future work of a similar nature. A scenario-based Monte Carlo simulation is performed to compare the performances of various state estimation methods. Experimental tests involving a low-speed fishing boat and a drone are performed to verify the performance and effectiveness of the proposed scheme. A separate performance analysis program with a graphical user interface is developed to analyze the simulation and field test results.

Quantifying the spatial extent, location and habitat associations of invasive tree species is critical to predict their future spread and prioritise areas for management. Species–environment relationship analyses are useful tools for understanding and predicting the potential geographical distribution of these species; however, such tools require rigorous and extensive data about species presence and, crucially, the area surveyed.Here, we describe a method for performing ground‐based visual surveys of invasive trees from a set of viewpoints that utilises laser rangefinder and global navigation satellite system (GNSS) technology to detect tree locations. We then highlight the novel use of geographical information system (GIS) viewsheds as a tool to define the area surveyed.Using the invasive conifer, Pinus radiata, as our target, we undertook a ground‐truthing exercise for 50 trees established in the wild to assess the accuracy of the method and determine the suitable spatial resolution for GIS data that would be used in subsequent species–environment relationship analyses. For these trees, location error was positively related to distance from the tree to the viewpoint. The calculated locations for all trees within 600 m of the observer were within 25 m of the location as determined by the GNSS unit, with a median location error of 4 m. These results indicate that data of a resolution suitable for mapping invasive trees can be efficiently collected over large areas. We also outline suggestions and instructions for computing the viewsheds to determine the surveyed area.This approach allows for efficient collection of accurate data on the occurrence of non‐native trees and the land area surveyed. These data can underpin species–environment relationship analyses that then form the basis of risk maps for areas prone to future invasion. Given the speed and accuracy with which data can be obtained using this method, and the use of standard and easily accessible field equipment and GIS software, we recommend this approach to other spatial and invasion ecologists. [ABSTRACT FROM AUTHOR]

Sweetness or sugar content, represented by soluble solids contents (SSC), is a vital quality trait in watermelon breeding which can be assessed by the refractive index method. However, sampling watermelon juice out of the pulp is a process that is both labor-intensive and error-prone. In this study, we developed an automatic SSC measurement system for watermelon breeding to improve efficiency and decrease costs. First, we built an automatic cutting system to cut watermelons into precise halves, in which a laser rangefinder is used to measure the distance from the upper surface of the watermelon to itself, and thus, the diameter is estimated. The experiments showed a high correlation between the estimated diameters and the ground truths, with and . Then, we built an automatic Brix measurement system to obtain the Brix data from a central point on the watermelon’s section, where an image analysis procedure is applied to locate the testing point. This is then transformed to the camera coordination system, and a refractometer is driven by a 3-axis robotic arm to reach the testing point. Brix measurement experiments were conducted using three vertical gaps and four lateral gaps between the probe of the refractometer and the pulp. The result showed that the best parameters were a vertical gap of 4 mm and a lateral gap of 2 mm. The average accuracy reached 98.74%, which indicates that this study has the potential to support watermelon breeding research.

Processing of batch signals of a laser rangefinder, designed for measuring the spacecraft orbit altitude by the pulsed method in the altitude range 180–370 km, is simulated for a photodetector operating in the charge-integration mode with allowance for the background solar radiation power. The rangefinder emits a batch of five 10-ns pulses with a pulse spacing of 250 μs. Digital processing of the echo signals received is based on the method of synchronous postdetector summation of the amplitudes of all pulses in a batch. When simulating the signal processing procedure, a 180–367.5 km strobe was used. The simulation program and its interface are described. The program generates normal Gaussian noise with the mean value and the variance dependent on the mean background radiation power. The probabilities of false alarm and correct signal detection are determined with allowance for the threshold number of photoelectrons for different numbers of signal photoelectrons in a single pulse of the batch. The altitude range measurement errors are analyzed throughout the strobe. [ABSTRACT FROM AUTHOR]

This paper focuses on integrating a laser rangefinder system with an anthropomorphic robot (NAO6—Aldebaran, United Robotics Group) to improve its sensory and operational capabilities, as part of a larger project concerning the use of these systems in “assisted living” activities. This additional sensor enables the robot to reconstruct its surroundings by integrating new information with that identified by the on-board sensors. Thus, it can identify more objects in a scene and detect any obstacles along its navigation path. This feature will improve the efficiency of navigation algorithms, increasing movement competence in environments where people live and work. Indeed, these environments are characterized by details and specificities within a range of distances that best suit the new robot design. The paper presents a laser finder integration project that consists of two different parts, which are as follows: the former, the mechanical part, provided the NAO robot’s head; the latter, the software, provided the robot with proper software drivers to enable integration of the new sensor with its acquisition system. Some experimental results in an actual environment are presented.

Recent implementations of sensory systems have addressed gait characterization in several assistive, rehabilitation and human-robot interaction scenarios. Sensors such as laser rangefinders, force platforms and motion tracking systems have been widely used to achieve legs’ position tracking, as well as to estimate gait spatio-temporal parameters. However, the validation of those measurements with a gold standard system is still lacking. In this sense, this work is aimed at proposing an online system for the estimation of gait parameters for walker-assisted gait with smart or robotic devices. Moreover, a validation study with an optoelectronic system was carried out. A group of 30 healthy volunteers was recruited. The trials were performed on a treadmill, where the subjects were asked to walk at 4 different speeds. The proposed system is equipped with a laser rangefinder to calculate the users’ legs position. Additionally, two adaptive filters, as well as a linear mathematical model were used to adjust the estimations of the users’ gait parameters. Results show that our proposed system is able to estimate the stride cadence and the step length with an error lower than 5% compared with the gold standard system. [ABSTRACT FROM AUTHOR]

In this paper, a method for trackless adjustment and testing of special purpose laser rangefinders and the scheme and design of the installation process developed for these purposes are presented. A new principle of the distance setting and its algorithmic correction using special software to improve the accuracy is implemented in the installation. The technical characteristics of the installation are given. [ABSTRACT FROM AUTHOR]

Abstract Background Plant height is an important morphological and developmental phenotype that directly indicates overall plant growth and is widely predictive of final grain yield and biomass. Currently, manually measuring plant height is laborious and has become a bottleneck for genetics and breeding programs. The goal of this research was to evaluate the performance of five different sensing technologies for field-based high throughput plant phenotyping (HTPP) of sorghum [Sorghum bicolor (L.) Moench] height. With this purpose, (1) an ultrasonic sensor, (2) a LIDAR-Lite v2 sensor, (3) a Kinect v2 camera, (4) an imaging array of four high-resolution cameras were evaluated on a ground vehicle platform, and (5) a digital camera was evaluated on an unmanned aerial vehicle platform to obtain the performance baselines to measure the plant height in the field. Plot-level height was extracted by averaging different percentiles of elevation observations within each plot. Measurements were taken on 80 single-row plots of a US × Chinese sorghum recombinant inbred line population. The performance of each sensing technology was also qualitatively evaluated through comparison of device cost, measurement resolution, and ease and efficiency of data analysis. Results We found the heights measured by the ultrasonic sensor, the LIDAR-Lite v2 sensor, the Kinect v2 camera, and the imaging array had high correlation with the manual measurements (r ≥ 0.90), while the heights measured by remote imaging had good, but relatively lower correlation to the manual measurements (r = 0.73). Conclusion These results confirmed the ability of the proposed methodologies for accurate and efficient HTPP of plant height and can be extended to a range of crops. The evaluation approach discussed here can guide the field-based HTPP research in general.

A line point cloud is a series of sequential discrete points acquired by a laser ranging sensor. Geometric properties estimation from line point clouds plays a crucial role in many applications, such as reverse engineering, industrial inspection, and autonomous navigation. This article proposes a new method for estimating the geometric properties, such as tangent, normal, curvature, and torsion, from line point clouds based on derivative estimation. According to the geometric meaning of the derivative, the derivative of a discrete function at a point is defined by using the Gaussian-weighted least squares, which is called the Gaussian-weighted discrete derivative (GDD) for short. By using the GDDs, classical differential geometry is discretized, and the geometric properties are estimated from a line point cloud based on its parametrized expression. Moreover, the noise intensity of the line point cloud is computed by using the Gaussian process regression for adaptive neighborhood adjustment to improve the estimation accuracy. The proposed method introduces the Gaussian weight into derivative estimation and estimates the geometric properties directly from line point clouds, which makes the estimation process reliable and understandable. The experimental results show that the proposed method is accurate, robust to noise, and suitable for different shapes. [ABSTRACT FROM AUTHOR]

Silicon photomultipliers (SiPM) have drawn considerable attention due to their superior sensitivity with a multi-pixel matrix structure. SiPM can be the choice of a detector for time of flight measurement which is one of the most promising applications in the field of light detection and ranging (LiDAR). In this work, we take advantage of SiPM and attempt to measure longer distances with a low peak power semiconductor laser under outdoor sunny and windy conditions. We achieved a long detection range of a few kilometers by using SiPM and a laser with a pulse energy of 9 µj at 0.905 µm and 3 dB enhancement in signal to noise ratio (SNR) by the implemented signal extraction algorithm. From the simulation performed, the minimum SNR value and detection probability were also determined for the outdoor field tests. [ABSTRACT FROM AUTHOR]

The calibration of a 3D laser rangefinder (LRF) and a camera is a key technique in the field of computer vision and intelligent robots. This paper proposes a new method for the calibration of a 3D LRF and a camera based on optimization solution. The calibration is achieved by freely moving a checkerboard pattern in front of the camera and the 3D LRF. The images and the 3D point clouds of the checkerboard pattern in various poses are collected by the camera and the 3D LRF respectively. By using the images, the intrinsic parameters and the poses of the checkerboard pattern are obtained. Then, two kinds of geometric constraints, line-to-plane constraints and plane-to-plane constraints, are constructed to solve the extrinsic parameters by linear optimization. Finally, the intrinsic and extrinsic parameters are further refined by global optimization, and are used to compute the geometric mapping relationship between the 3D LRF and the camera. The proposed calibration method is evaluated with both synthetic data and real data. The experimental results show that the proposed calibration method is accurate and robust to noise. [ABSTRACT FROM AUTHOR]

This paper proposes an improved method for the calibration of a 2D LiDAR or a planar scanning laser rangefinder with respect to a camera, which uses the same checkerboard target as in the camera calibration. To address one of the drawbacks in the LiDAR calibration with a checkerboard, the sensitivity to checkerboard poses, laser points on the checkerboard are obtained from both the originally positioned LiDAR and the same LiDAR vertically rotated from the original position, in the proposed calibration. They construct the additional constraints with the normal vector of the checkerboard, and strengthen the basic point-on-plane constraints in the LiDAR calibration with a checkerboard. However, in practice, the LiDAR rotation can be imprecise. Thus, we further develop the calibration procedure and examine its calibration performance, in the presence of such impreciseness in the LiDAR rotation. A performance analysis is conducted with synthetic noisy data, and it is confirmed that the proposed calibration yields smaller error in the parameter estimation than a conventional baseline calibration method. Subsequently, we examine the calibration performance with real data, where the proposed calibration is carried out by building a calibration system. It is shown that the proposed calibration also has more consistency in the parameter estimation. For further study, we compare the proposed calibration based on point-on-plane constraints with a calibration based on point-to-point constraints, and show that the proposed calibration, with easier data acquisition, yields comparable results. [ABSTRACT FROM AUTHOR]

An integrated receiver–time-to-digital converter (TDC) chip set is developed for pulsed time-of-flight (TOF) laser rangefinding. The receiver detects the current pulse from the optical detector and produces a timing mark for the TDC. The receiver uses time mode walk error compensation scheme achieving <±2.5-mm residual timing-walk error within a dynamic range of ~1:40 000. The multichannel TDC measures the time position, width, and rise time of the echo pulses simultaneously with ~10-ps precision. Both chips are manufactured in 0.35- $\mu \text{m}$ complementary metal–oxide–semiconductor (CMOS) technology. The functionality of the chip set was demonstrated in a laser radar platform using 12 W and 3-ns optical pulses produced by a laser diode (LD). Measurement accuracy of ~ ±3 mm was achieved with noncooperative targets at a distance range of a few tens of meters within an amplitude range of received echoes of 1:40 000. [ABSTRACT FROM AUTHOR]

The first experiments on lunar laser ranging, which were carried out by Soviet and American scientists, date back to the early 1960s. Those studies refined the main parameters of the Earth–Moon system and achieved a considerable progress in solving the problems of selenodesy, astrometry, geodesy, and geophysics. The beginning of space exploration of the Moon and the planets of the Solar System gave scientists and engineers worldwide an opportunity to conduct both ground-based and space observations using laser reflectors onboard low-orbit and geodynamic satellites, space probes, and robotic rovers on the surface of the Moon and planets. Future remote and contact scientific studies of the lunar surface are expected to provide new information about the Earth–Moon system. [ABSTRACT FROM AUTHOR]

The article presents methods of long range distance measurements using pulsed lasers and the Time of Flight principle. Various algorithms of laser distance measurements with digital acquisition of echo pulses (acquisition of a signal’s full waveform) are presented. The main focus of work is concentrated on the method of distance measurements developed by the authors. With this method, during laboratory trials, a total measurement error of one centimeter was achieved using a 905 nm pulsed laser diode and pulse width of 39 ns. The maximum range of measurements with such high precision is limited only by a signal to noise ratio, duration of measurements and atmospheric conditions. All algorithms were implemented in a laser rangefinder module developed by the authors. Simulations and laboratory experiments were conducted and algorithm’s accuracy and precision were tested for various SNR conditions and changing distances.