Lidar System For Measurement Research Articles

Intelligent extraction of road cracks based on vehicle laser point cloud and panoramic sequence images

In light of the limited efficacy of conventional methods for identifying pavement cracks and the absence of comprehensive depth and location data in two-dimensional photographs, this study presents an intelligent strategy for extracting road cracks. This methodology involves the integration of laser point cloud data obtained from a vehicle-mounted system and a panoramic sequence of images. The study employs a vehicle-mounted LiDAR measurement system to acquire laser point cloud and panoramic sequence image data simultaneously. A convolutional neural network is utilized to extract cracks from the panoramic sequence image. The extracted sequence image is then aligned with the laser point cloud, enabling the assignment of RGB information to the vehicle-mounted three dimensional (3D) point cloud and location information to the two dimensional (2D) panoramic image. Additionally, a threshold value is set based on the crack elevation change to extract the aligned roadway point cloud. The three-dimensional data pertaining to the cracks can be acquired. The experimental findings demonstrate that the use of convolutional neural networks has yielded noteworthy outcomes in the extraction of road cracks. The utilization of point cloud and image alignment techniques enables the extraction of precise location data pertaining to road cracks. This approach exhibits superior accuracy when compared to conventional methods. Moreover, it facilitates rapid and accurate identification and localization of road cracks, thereby playing a crucial role in ensuring road maintenance and traffic safety. Consequently, this technique finds extensive application in the domains of intelligent transportation and urbanization development. The technology exhibits significant promise for use in the domains of intelligent transportation and city development.

Validation of Solid-State LiDAR Measurement System for Ballast Geometry Monitoring in Rail Tracks

The inspection and maintenance of track ballast are fundamental tasks for the preservation of the condition of railway networks. This work presents an application based on a low-cost solid-state LiDAR system, which allows the user to accurately measure the ballast geometry from a mobile inspection trolley or draisine. The solid-state LiDAR system, the LiVOX Avia, was validated on a test track through comparison with a traditional static LiDAR system, the Faro Focus 3D. The results show a standard deviation of around 6 mm for the solid-state LiDAR system. The LiVOX system also provides the capability to measure the ballast digital elevation model and profiles. The LiVOX results are in agreement with those obtained from the Faro Focus. The results demonstrate that the LiVOX system can sufficiently measure even the displacement of a single layer of ballast stones typically between 2.5 cm and 5 cm. The data provided can be easily digitalized using image processing tools and integrated into geographic information systems for infrastructure management.

A measurement point planning method based on lidar automatic measurement technology.

The automated measurement mode in the lidar measurement system (LMS) has advantages unmatched by other measurement equipment in measuring the surface of large components. Before starting the automatic measurement mode, it is necessary to plan the measurement guide points for the measurement area. The rationality of the measurement points planning will directly affect the quality of the measurement data and the measurement efficiency. This paper proposes a planning method for measurement points on the outer surface of components based on lidar automatic measurement technology. First, the geometric features to be measured are discretized into spatial point cloud data. Second, the edge points of the point clouds are extracted and indented to meet the measurement requirements, which improves the measurement accuracy of the edge areas. Finally, by planning the path of the measurement points, the laser beam of the lidar can traverse the points of the measurement features with the shortest paths. Through the analysis of two cases, the method proposed in this paper will provide a huge advantage for the LMS: (1) The edge points of all features can be identified and indented in a short time to ensure the measurement accuracy of the edge areas of each measurement feature. (2) Through the measurement path planning, the repetitive measurement path of the lidar can be significantly reduced, improving the measurement efficiency. The method proposed in this paper has important guiding significance for the subsequent measurement station planning and constructing large-scale spatial measurement fields of the LMS.

Ground-based LiDAR measurement system integrating BeiDou/GNSS positioning and 5G communication

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Double-Threshold Segmentation of Panicle and Clustering Adaptive Density Estimation for Mature Rice Plants Based on 3D Point Cloud

Crop density estimation ahead of the combine harvester provides a valuable reference for operators to keep the feeding amount stable in agriculture production, and, as a consequence, guaranteeing the working stability and improving the operation efficiency. For the current method depending on LiDAR, it is difficult to extract individual plants for mature rice plants with luxuriant branches and leaves, as well as bent and intersected panicles. Therefore, this paper proposes a clustering adaptive density estimation method based on the constructed LiDAR measurement system and double-threshold segmentation. The Otsu algorithm is adopted to construct a double-threshold according to elevation and inflection intensity in different parts of the rice plant, after reducing noise through the statistical outlier removal (SOR) algorithm. For adaptively parameter adjustment of supervoxel clustering and mean-shift clustering during density estimation, the calculation relationship between influencing factors (including seed-point size and kernel-bandwidth size) and number of points are, respectively, deduced by analysis. The experiment result of density estimation proved the two clustering methods effective, with a Root Mean Square Error (RMSE) of 9.968 and 5.877, and a Mean Absolute Percent Error (MAPE) of 5.67% and 3.37%, and the average accuracy was more than 90% and 95%, respectively. This estimation method is of positive significance for crop density measurement and could lay the foundation for intelligent harvest.

Digital evaluation of leaf area of an individual tree canopy in the apple orchard using the LIDAR measurement system

This paper compares LIDAR and manual measurements of leaf area in orchards. The LIDAR measurements were performed in real orchard conditions. LIDAR data were used to count the number of points and to measure the canopy volume of individual volume elements. Manual measurements included defoliation, counting and leaf area measurements. Both types of measurements were performed in 8 volume elements for 20 apple trees of three different ages and varieties (‘Golden delicious’, ‘Jonagold’ and ‘Gala’). Using regression analysis, we estimated the relation between number of points in the cloud, canopy volume (both LIDAR measurements) and the leaf area (manual measurement). The maximum value of the correlation coefficient was 0.87816, when established from the relation between the number of points in the cloud and the canopy leaf area. The maximum value of the correlation coefficient was 0.80167, when established between the volume of tree canopy volume element and the leaf area.

LiDAR measurement system and the calibration method of loading robot

To carry out the measurement of vehicle body position and dimension of loading robot before loading, an intelligent vehicle body measurement system based on two-dimensional LiDAR was provided, and the calibration method of this system was studied as a key point. The two-dimension LiDAR was driven by rotating the platform, and the three-dimensional information of car body measured was obtained by using the single two-dimensional laser radar. In allusion to the complexity of calibration method of LiDAR measurement system and the difficulty in making calibration pieces, a system parameter calibration method was proposed based on 321 coordinate system building method, and mathematical models of calibration was established, with the principle and procedure of calibration method in detail. Measurement system was set up in a laboratory to carry out calibration experiment and measurement experiment on simulation vehicle body, and the measurement experiment for real vehicle body was conducted outside. The experiment result shows that the maximum measurement error of vehicle body size and length of this measurement system was 26.4 mm; maximum angle measurement error was 0.18 degree, which fully meets the precision requirements of loading.

户外型探测臭氧和气溶胶激光雷达系统研制

户外型探测臭氧和气溶胶激光雷达系统研制

HIGH RESOLUTION AIRBORNE SHALLOW WATER MAPPING

Abstract. In order to meet the requirements of the European Water Framework Directive (EU-WFD), authorities face the problem of repeatedly performing area-wide surveying of all kinds of inland waters. Especially for mid-sized or small rivers this is a considerable challenge imposing insurmountable logistical efforts and costs. It is therefore investigated if large-scale surveying of a river system on an operational basis is feasible by employing airborne hydrographic laser scanning. In cooperation with the Bavarian Water Authority (WWA Weilheim) a pilot project was initiated by the Unit of Hydraulic Engineering at the University of Innsbruck and RIEGL Laser Measurement Systems exploiting the possibilities of a new LIDAR measurement system with high spatial resolution and high measurement rate to capture about 70 km of riverbed and foreland for the river Loisach in Bavaria/Germany and the estuary and parts of the shoreline (about 40km in length) of lake Ammersee. The entire area surveyed was referenced to classic terrestrial cross-section surveys with the aim to derive products for the monitoring and managing needs of the inland water bodies forced by the EU-WFD. The survey was performed in July 2011 by helicopter and airplane and took 3 days in total. In addition, high resolution areal images were taken to provide an optical reference, offering a wide range of possibilities on further research, monitoring, and managing responsibilities. The operating altitude was about 500 m to maintain eye-safety, even for the aided eye, the airspeed was about 55 kts for the helicopter and 75 kts for the aircraft. The helicopter was used in the alpine regions while the fixed wing aircraft was used in the plains and the urban area, using appropriate scan rates to receive evenly distributed point clouds. The resulting point density ranged from 10 to 25 points per square meter. By carefully selecting days with optimum water quality, satisfactory penetration down to the river bed was achieved throughout the project. During the data processing meshes for multiple purposes like monitoring sediment transport or accumulation and hydro-dynamic numeric modeling were generated. The meshes were professionally conditioned considering the adherence of, both, geometric and physical mesh quality criterions. Whereas the research is focused on the design and implementation of monitoring database structures, the airborne hydrographic data are also made available for classical processing means (cross sections, longitudinal section).

A lidar for water vapour measurements in daytime at Lampedusa, Italy

ENEA is planning to develop a lidar system for measurement of the vertical profi le of water vapour mixing ratio in daytime at a remote site, the Station for Climate Observations located in Lampedusa, Italy. The Raman lidar technique has been retained because of its experimental simplicity with respect to DIAL, and the UV spectral range has been chosen because Raman cross-sections and detector effi ciencies are larger. For a wavelength larger than ~ 300 nm the signal is limited in daytime by sky background, but extinction is acceptable, and the aims of the system can be reached with a strong laser source. The 355 nm wavelength of a frequency-tripled Nd:YAG laser has been retained as this laser source permits to reach a large pulse energy while keeping the system simple to operate. Geometrical form factor calculations need to be performed to evaluate the near-range overlap between the laser beam and the fi eld-of-view of the receiver. Among several options, a dual-receiver system has been retained to account for the several orders of magnitude expected in the backscattered signal intensity: a smaller receiver, with a primary mirror of 200 mm diameter for the 0.2-1 km range, and a larger 500 mm receiver for the 1-3 km range.

Raman lidar for profiling atmospheric CO2

Based on laser atmosphere backscattering spectrum, the design and experiment of a Raman lidar system for measurement of atmospheric CO2 are presented. 354.7nm third harmonic of Nd∶YAG laser is transmitted with 350mJ pulse energy and repetition rate of 20Hz. The receiver employs a photomultiplier tube with quantum efficiency of 25% and 200MHz photon counter, and it detects Raman backscattering 371.66nm(shift 1285cm-1) signal. At 1h integration, the signal to noise ratio below 2.5km is greater than 8. Combinatorial filter is used to reject interference presented by 354.7nm intense Mie-Rayleigh backscattering and 375.4nm Raman backscattering from O2. We compare the Raman return signal at 371.66nm from atmospheric CO2 with the reference Raman return signal at 386.7nm from atmospheric N2 to retrieve the atmospheric CO2 concentration.

Intensity-modulated, stepped frequency cw lidar for distributed aerosol and hard target measurements

A compact frequency-modulated, continuous wave (FM-cw) lidar system for measurement of distributed aerosol plumes and hard targets is presented. The system is based on intensity modulation of a laser diode and quadrature detection of the return signals. The advantages of using laser diode amplitude modulation and quadrature detection is a large reduction in the hardware required for processing and storing return signals as well as the availability of off-the-shelf integrated electronic components from the wireless and telecommunication communities. Equations to invert the quadrature signal components and determine spatial distributions of multiple targets are derived. Spatial scattering intensities are used to extract aerosol backscatter coefficients, which can then be directly compared to microphysics aerosol models for environmental measurements. Finally, results from laboratory measurements with a monostatic FM-cw lidar system with both hard targets and aerosols are discussed.

Development of a differential-absorption lidar system for measurement of atmospheric atomic mercury by use of the third harmonic of an LDS-dye laser

A differential-absorption lidar system that uses a long-life transmitter for monitoring of atomic-mercury concentrations in the atmosphere has been developed. The third harmonic of a tunable dye laser with LDS 765 dye pumped by the second harmonic of a Nd:YAG laser was used as the emitted beam from the transmitter. By use of this system, atmospheric concentrations of atomic mercury of less than 0.4 part in 10(12) were measured. The time trend of the measured concentration agreed with that obtained by a conventional gold amalgamation method combined with atomic absorption spectroscopy on the ground.

Evaluation of differential absorption lidar (DIAL) measurement error by simultaneous DIAL and null profiling

A differential absorption lidar system for measurement of trace atmospheric substances in the visible and UV regions is developed. The system is based on a pair of Nd:YAG pumped dye lasers, each capable of emitting two wavelengths on alternate shots. The measurement error of the system was evaluated by measurement of tropospheric O3 using two identical differential absorption lidar (DIAL) pairs, from which two null profiles and four DIAL profiles are obtained simultaneously. The null profiles, obtained for both the on and off wavelengths used in DIAL measurement, are useful to evaluate systematic DIAL measurement error due to beam misalignment. The null profiles show that this systematic error is at most 1.3%. The total DIAL measurement error is about 5%, most of which can be attributed to statistical error.

Frequency stabilization of a Ho:Tm:YLF laser to absorption lines of carbon dioxide

A single-frequency Ho:Tm:YLF laser, operating at an eye-safe wavelength of 2 mum, has been developed with tuning characteristics optimized for spectroscopy of absorption features. The laser frequency was stabilized to three different absorption lines of carbon dioxide by a wavelength modulation technique. Long-term frequency drift has been eliminated from the laser, and shorter-term jitter has been reduced to within 13.5 MHz of the absorption line center. This stabilized laser is an ideal injection seed source for a differential absorption lidar system for measurement of atmospheric gases.

Ozone and aerosol distributions and air mass characteristics over the South Pacific during the burning season

In situ and laser remote measurements of gases and aerosols were made with airborne instrumentation to establish a baseline chemical signature of the atmosphere above the South Pacific Ocean during the NASA Global Tropospheric Experiment (GTE)/Pacific Exploratory Mission‐Tropics A (PEM‐Tropics A) conducted in August‐October 1996. This paper discusses general characteristics of the air masses encountered during this experiment using an airborne lidar system for measurements of the large‐scale variations in ozone (O3) and aerosol distributions across the troposphere, calculated potential vorticity (PV) from the European Centre for Medium‐Range Weather Forecasting (ECMWF), and in situ measurements for comprehensive air mass composition. Between 8°S and 52°S, biomass burning plumes containing elevated levels of O3, over 100 ppbv, were frequently encountered by the aircraft at altitudes ranging from 2 to 9 km. Air with elevated O3 was also observed remotely up to the tropopause, and these air masses were observed to have no enhanced aerosol loading. Frequently, these air masses had some enhanced PV associated with them, but not enough to explain the observed O3 levels. A relationship between PV and O3 was developed from cases of clearly defined O3 from stratospheric origin, and this relationship was used to estimate the stratospheric contribution to the air masses containing elevated O3 in the troposphere. The frequency of observation of the different air mass types and their average chemical composition is discussed in this paper.

Large‐scale air mass characteristics observed over western Pacific during summertime

Remote and in situ measurements of gases and aerosols were made with airborne instrumentation to investigate the sources and sinks of tropospheric gases and aerosols over the western Pacific during the NASA Global Tropospheric Experiment (GTE)/Pacific Exploratory Mission‐West A (PEM‐West A) conducted in September–October 1991. This paper discusses the general characteristics of the air masses encountered during this experiment using an airborne lidar system for measurements of the large‐scale variations in ozone (O3) and aerosol distributions across the troposphere and airborne in situ instrumentation for comprehensive measurements of air mass composition. In low latitudes of the western Pacific the airflow was generally from the east, and under these conditions the air was observed to have low aerosol loading and low ozone levels throughout the troposphere. Ozone was found to be below 10 parts per billion volume (ppbv) near the surface to 40–50 ppbv in the middle to upper troposphere. In the middle and high latitudes the airflow was mostly westerly, and the background O3 was generally less than 55 ppbv. On 60% of the PEM‐West A flights, O3 was observed to exceed these levels in regions that were determined to be associated with stratospheric intrusions. In convective outflows from typhoons, near‐surface air with low ozone (<25 ppbv) was transported into the upper troposphere (>10 km). Several cases of continental plumes from Asia were observed over the Pacific during westerly flow conditions. These plumes were found in the lower troposphere with ozone levels in the 60–80 ppbv range and enhanced aerosol scattering. At low latitudes over the central Pacific the troposphere primarily contained air with background or low ozone levels; however, stratospherically influenced air with enhanced ozone (40–60 ppbv) was observed several times in the lower troposphere. The frequency of observation of the air masses and their average chemical composition are also discussed in this paper.

Airborne differential absorption lidar system for measurements of atmospheric water vapor and aerosols

An airborne differential absorption lidar (DIAL) system has been developed at the NASA Langley Research Center for remote measurements of atmospheric water vapor (H(2)O) and aerosols. A solid-state alexandrite laser with a 1-pm linewidth and > 99.85% spectral purity was used as the on-line transmitter. Solid-state avalanche photodiode detector technology has replaced photomultiplier tubes in the receiver system, providing an average increase by a factor of 1.5-2.5 in the signal-to-noise ratio of the H(2)O measurement. By incorporating advanced diagnostic and data-acquisition instrumentation into other subsystems, we achieved additional improvements in system operational reliability and measurement accuracy. Laboratory spectroscopic measurements of H(2)O absorption-line parameters were perfo med to reduce the uncertainties in our knowledge of the absorption cross sections. Line-center H(2)O absorption cross sections were determined, with errors of 3-6%, for more than 120 lines in the 720-nm region. Flight tests of the system were conducted during 1989-1991 on the NASA Wallops Flight Facility Electra aircraft, and extensive intercomparison measurements were performed with dew-point hygrometers and H(2)O radiosondes. The H(2)O distributions measured with the DIAL system differed by ≤ 10% from the profiles determined with the in situ probes in a variety of atmospheric conditions.

DIAL technique for pollution monitoring: improvements and complementary systems

Improvements to and complementary systems for a differential absorption lidar system for field work are discussed. A dual-wavelength laser and a dual-wavelength detection system, which make DIAL with simultaneous lidar measurements at two wavelengths possible, are described. A multiwavelength measurement routine, which will improve accuracy and detection limits, is proposed. A dual-beam lidar system for measurements of plume velocity is also described.