Laser Meter Research Articles

Free oscillations of water level in the Posyet Gulf bays (the Sea of Japan)

The results of the experiments on the registration of hydrosphere pressure variations are analyzed. The experiments were conducted in 2011, 2012, and 2014 using the laser meter ofhydrosphere pressure variations and the laser hydrophone in some bays of the Posyet Gulf in the Sea of Japan. Basic attention is given to the wind waves and fundamental modes of free oscillations in the bays.

Design of a scanning laser meter for monitoring the spatio-temporal evolution of snow depth and its application in the Alps and in Antarctica

Abstract. Although both the temporal and spatial variations of the snow depth are usually of interest for numerous applications, available measurement techniques are either space-oriented (e.g. terrestrial laser scans) or time-oriented (e.g. ultrasonic ranging probe). Because of snow heterogeneity, measuring depth in a single point is insufficient to provide accurate and representative estimates. We present a cost-effective automatic instrument to acquire spatio-temporal variations of snow depth. The device comprises a laser meter mounted on a 2-axis stage and can scan ≈ 200 000 points over an area of 100–200 m2 in 4 h. Two instruments, installed in Antarctica (Dome C) and the French Alps (Col de Porte), have been operating continuously and unattended over 2015 with a success rate of 65 and 90 % respectively. The precision of single point measurements and long-term stability were evaluated to be about 1 cm and the accuracy to be 5 cm or better. The spatial variability in the scanned area reached 7–10 cm (root mean square) at both sites, which means that the number of measurements is sufficient to average out the spatial variability and yield precise mean snow depth. With such high precision, it was possible for the first time at Dome C to (1) observe a 3-month period of regular and slow increase of snow depth without apparent link to snowfalls and (2) highlight that most of the annual accumulation stems from a single event although several snowfall and strong wind events were predicted by the ERA-Interim reanalysis. Finally the paper discusses the benefit of laser scanning compared to multiplying single-point sensors in the context of monitoring snow depth.

A measuring method for large antenna assembly using laser and vision guiding technology

Abstract In this paper a new conception of a measuring method is proposed to assist precision automatic assembly of large radar antenna. Different from conventional 6-DOF tracking methods, the measuring system decomposes the measurement task into several independent steps. The measuring system consists of a camera, two laser distance meters, two position sensitive detectors (PSD) and an inclination angle sensor. The camera is adopted to guide antenna position and orientation adjustment over a large space. Laser meters and PSD sensor is used to precisely measure the position and orientation of radar antenna. To improve the practicability of measuring system, a robust vision measurement method is proposed. The mathematical models and practical calibration methods for measurement are elaborated. The preliminary experimental results agree with the methods currently being used for orientation and position measurement. The measuring method provides an alternative choice for the metrology in precision assembly. By using the method proposed in this paper, the measuring system can achieve a measurement accuracy of approximately 1 mm, which meets the accuracy requirement of large radar antenna automatic assembly application. Besides, the measuring method provides an alternative solution for large scale metrology which take the environmental impact into account.

Compensation for the temperature effect on operation of laser interferometers

A temperature-compensated design of laser meters of hydrosphere pressure variations and laser hydrophones has been developed and introduced. Owing to this design, it is possible to perform long-term measurements without tuning the optical section of an instrument.

Лазерный измеритель характеристик атмосферных аэрозольных неоднородностей в видимом и ультрафиолетовом диапазонах спектра

Лазерный измеритель характеристик атмосферных аэрозольных неоднородностей в видимом и ультрафиолетовом диапазонах спектра

APPLICATIONS OF STRUCTURED IN SPACE AND TIME laser beam in vibrometer

Developed laser meters vibratory, allowing simultaneous capture of three spatial components displacement surface - two corner and one progressive. To measure the angular displacement components used mirror component reflected by the surface of the radiation, and translational - diffuse. Repetitively pulsed mode laser provides a measurement of the frequency of vibration. It is shown that a primation in vibrometers structured in space and time of the laser beams, the performance of vibration meters and extends the range of the measured parameters.

Laser Gas-Analyser for Monitoring a Source of Gas Pollution

Currently, the problem of growing air pollution of the Earth is of relevance. Many countries have taken measures to protect the environment in order to limit the negative anthropogenic impacts. In such a situation an objective information on the actual content of pollutants in the atmosphere is of importance. For operational inspection of the pollutant concentrations and for monitoring pollution sources, it is necessary to create high-speed high-sensitivity gas analysers. Laser meters are the most effective to provide operational remote and local inspection of gas pollution of the Earth atmosphere. Laser meter for routine gas analysis should conduct operational analysis of the gas mixture (air). For this a development of appropriate information support is required. Such information support should include a database with absorption coefficients of pollutants (specific to potential sources of pollution) at possible measuring wavelengths (holding data for a particular emitter of the laser meter) and an efficient algorithms to search the measuring wavelengths and conduct a quantitative analysis of gas mixtures. Currently, the issues, important for practice and related to the development of information support for the laser gas analyzer to conduct important for practice routine measurements remain unclear. In this paper we develop an algorithm to provide an operational search of the measuring wavelengths of laser gas analyser and an algorithm to recover quantitively the gaseous component concentrations of controlled gas mixture from the laser multi-spectral measurements that take into account a priori information about the source-controlled gas pollution and do not require a large amount of computation. The method of mathematical simulation shows the effectiveness of the algorithms described both for seach of measuring wavelengths and for quantitative analysis of gas releases.

Studying the variability of the wind wave period

Analyzed are the experimental data on the range of the sea wind waves obtained using a laser meter of hydrospheric pressure variations in 2007, 2010, 2011, and 2012 at different points of the shelf of the Sea of Japan. It is demonstrated that the variations of wind wave periods at their leaving the zone of cyclonic action can be associated not only with the dispersion but also with the Doppler effect and variations of the wind speed and wind direction in the zone of cyclonic action. Carried out was the analysis of the results of the processing of experimental data of the laser meter of hydrospheric pressure variations and the mobile laser meter of hydrospheric pressure variations; this analysis revealed that the transformation of wind waves with the decrease in the period and energy takes place in the case of their movement along the shelf of the decreasing depth.

SURVEYING WORLD HERITAGE ISLAMIC MONUMENTS IN NORTH AFRICA: EXPERIENCES WITH SIMPLE PHOTOGRAMMETRIC TOOLS AND NO PREVIOUS PLANNING

Abstract. Different experiences of surveys of Islamic monuments from different sites of Tunisia, Algeria and Morocco are presented. They have been made with simple tools: one photographic camera and a laser meter, without a previous planning or prevision for the survey, profiting from visits organized during scientific meetings to which the author was invited. Some of these monuments belong to sites included in the World Heritage List, but no metric documents or only low quality information is available. Monumental Almohad gates from Rabat and Marrakech, the al-Badi palace of Marrakech, the minarets of Mansura and the Qala of Beni Hammad, the dome in front of the mihrab of the mosque of Tlemcen are some of the examples to be presented. The methodology applied is based on ideas and tools acquired in CIPA meetings proving the usefulness of these encounters but supporting the idea that "providers" should provide tools and methods and "users" should be responsible for documentation, never missing the opportunity of acquiring knowledge from the heritage during the survey process.

Design and development of guidance navigation and control algorithms for spacecraft rendezvous and docking experimentation

This paper presents the design of the GNC system of a ground test-bed for spacecraft rendezvous and docking experiments. The test-bed is developed within the STEPS project (Systems and Technologies for Space Exploration). The facility consists of a flat floor and two scaled vehicles, one active chaser and one “semi-active” target. Rendezvous and docking maneuvers are performed floating on the plane with pierced plates as lifting systems. The system is designed to work both with inertial and non-inertial reference frame, receiving signals from navigation sensors as: accelerometers, gyroscopes, laser meter, radio finder and video camera, and combining them with a digital filter. A Proportional-Integrative-Derivative control law and Pulse Width Modulators are used to command the cold gas thrusters of the chaser, and to follow an assigned trajectory with its specified velocity profile. The design and development of the guidance, navigation and control system and its architecture—including the software algorithms—are detailed in the paper, presenting a performance analysis based on a simulated environment. A complete description of the integrated subsystems is also presented.

Multi-Sensor Localization and Navigation for Remote Manipulation in Smoky Areas

When localizing mobile sensors and actuators in indoor environments laser meters, ultrasonic meters or even image processing techniques are usually used. On the other hand, in smoky conditions, due to a fire or building collapse, once the smoke or dust density grows, optical methods are not efficient anymore. In these scenarios other type of sensors must be used, such as sonar, radar or radiofrequency signals. Indoor localization in low-visibility conditions due to smoke is one of the EU GUARDIANS [ 1 ] project goals. The developed method aims to position a robot in front of doors, fire extinguishers and other points of interest with enough accuracy to allow a human operator to manipulate the robot's arm in order to actuate over the element. In coarse-grain localization, a fingerprinting technique based on ZigBee and WiFi signals is used, allowing the robot to navigate inside the building in order to get near the point of interest that requires manipulation. In fine-grained localization a remotely controlled programmable high intensity LED panel is used, which acts as a reference to the system in smoky conditions. Then, smoke detection and visual fine-grained localization are used to position the robot with precisely in the manipulation point (e.g., doors, valves, etc.).

Multisensor remote robot localization and manipulation in low-visibility conditions

Indoor sensor localization is a complex task. In normal circumstances, laser meters, ultrasonic meters or even image processing may be used to estimate the position of a given node at a particular moment. Indoor localization in low-visibility conditions due to smoke is one of the EU GUARDIANS (GUARDIANS (2010)) project goals. When smoke density grows, optical sensors are not efficient anymore. In these scenarios other sensors must be studied, such as sonar, radar or radio-frequency signals. The developed multisensor method aims to position a robot in front of doors, fire extinguishers and other points of interest with enough accuracy to, know the doorknob position, grasp it and open the door. In the coarse grain localization, ZigBee and WiFi signals are used to calculate the localization of the robot inside a building and guide it near enough to the point of interest to glimpse a programmable high intensity LED panel. Then, smoke detection and visual fine grained localization are used to position the robot with precision.

Mobile laser meter of hydrosphere pressure variations

A device for measuring hydrosphere pressure variations at depths of down to 1000 m in the frequency range of 0–1000 Hz with an accuracy of 10–30 mPa is described.

Free Flap Blood Flow Evaluated Using Two-Dimensional Laser Speckle Flowgraphy

Objective. We investigated the efficiency of laser speckle flowgraphy for evaluating blood flow in free flaps used for plastic surgery. Methods. We measured blood flow using a visual laser meter capable of providing two-dimensional color graphic representations of flow distribution for a given area using a dynamic laser speckle effect. Using laser speckle flowgraphy, we examined the blood flow of 20 free flaps applied following the excision of head and neck tumors. Results. After anastomosis of the feeding and draining blood vessels and sewing the flap, musculocutaneous (MC) flaps showed significantly lower blood flow than jejunal or omental flaps (P < .05). The ratio of blood flow decrease from the edge to the center was significantly greater in MC flaps than in jejunal or omental flaps (P < .001). Conclusion. Laser speckle flowgraphy is useful for the perioperative measurement of blood flow in free flaps used in plastic surgery. This method is a highly useful, practical, and reliable tool for assessing cutaneous blood flow and is expected to be applicable to several clinical fields.

A fuzzy rule-based system for predicting the live weight of Holstein cows whose body dimensions were determined by image analysis

The aim of this study was to determine the body measurement of Holstein cows through image analysis (IA) and to estimate their live weight (LW) by means of a fuzzy rule-based model using the body measurements. For this purpose, a photography environment was established at a dairy cattle farm where a large number of cows were kept. First, digital photographs of each animal were synchronously taken from different directions with Canon EOS 400D cameras. At the same time, body dimensions, namely wither height (WH), hip height (HH), body length (BL), and hip width (HW), of the cows were manually measured using a laser meter and measuring stick. The LWs of the cows were found with a weighing scale and the data were automatically saved on a computer. In the second stage, the photos were analyzed by IA software developed in the Delphi programming language and body measurements were computed. Manually measured values were very close to IA results. Finally, a fuzzy system was developed by using these body measurements. This fuzzy system was developed by using MATLAB software. Weights that were estimated with the developed knowledge-based system were compared with those found by the platform scale. The correlation coefficient was calculated (r = 0.99). There was a statistically meaningful relationship between the compared data. The developed system can be used confidently, and the system on which the experiments were performed can be modeled successfully.

Multiple calibration bench for focal length of cameras by means of laser distance meter

The calibration of the cameras used in close-range photogrammetry is usually performed using auxiliary elements with known geometry and/or dimensions, through one or several photographs of elements with geometrical restrictions, which enable the calculation of the different parameters needed. This research suggests an improvement in these procedures through the use of one or several laser meters. The method is based on the use of calibration pillars in a laboratory, in which the cameras and laser meters subject to calibration are fixed. The cameras are calibrated by determining the relative positions of all the devices at the same time, which enables the application of the algorithm designed for hybrid laser-camera systems used for measuring in civil engineering and robotics. For this purpose, photographs and measurements are taken by laser meters over a moving object of unknown geometry and dimensions.

Super-low-frequency laser instrument for measuring hydrosphere pressure variations

The operating principle and specifications of a laser meter for measuring hydrosphere pressure variations are described in this article. The meter was designed to measure the hydrosphere pressure variations to a depth of 500 m within the frequency range of 0–1000 Hz at the level of background oscillations. Some results obtained using the apparatus under consideration when recording sea oscillations and waves of natural and artificial origin are presented.

Flat elements on buildings using close-range photogrammetry and laser distance measurement

The dimensions of building facades and window apertures are usually measured by direct methods using tapes and plummets. These methods require several operators, are slow and in many cases imply working in conditions of high risk. This paper proposes to replace these procedures by indirect methods based on close-range photogrammetry and laser distance measurement, resulting in a low cost, quick, simple and safe method. The method is based on taking three photographs with a digital camera and measuring the three distances with a laser meter, with both instruments mounted on a support that is calibrated in multiple turning positions in order to simultaneously measure different elements on a plane that has regular or irregular geometry.

Focus on test and measurement

Focus on test and measurement

Effect of noise and vibration on the performance of a particle concentration laser meter and optimization of its parameters

Spurious illumination penetrating into a gas duct adversely affects the performance of a laser gage measuring the concentration of solid particles dispersed in the air flow. The noise and gas duct vibration caused by the noise and vibration of the flow driver and other sources mechanically connected to the gas duct modulate the spurious radiation so that it may generate a signal that is perceived as a useful one by a photodetector. The noise-and vibration-modulated spurious illumination, as well as its optical-to-electric conversion with consideration for the spectral characteristics and the connection of the photodetector to the laser gage, is analyzed. From the amplitude and frequency properties of real noise and vibration sources causing the gas duct walls, on which the laser gage is mounted, to vibrate, the effect of the parasitic illumination is estimated. The operating parameters of a laser gage with double amplitude modulation and subsequent double synchronous detection, which make it possible to considerably improve its noise immunity, are proposed.