STRICT GEOMETRIC CALIBRATION OF AN UNDERWATER LASER TRIANGULATION SYSTEM

Abstract. This paper will describe a novel approach for the calibration of an underwater laser triangulation system. Underwater triangulation systems, consisting of a line laser and a camera can be used to determine the geometry of submerged objects or the topography of a water body bottom. Placing camera and laser line projector inside a waterproof housing leads to refraction effects at the air-glass-water interfaces, both of the laser light-sheet and image rays. This implies a deformed laser plane in the water and a curved line on the object surface. The proposed approach strictly models the geometry between camera, laser and housing. First experiments show, that the calibration method can be applied for water depth measurements with accuracies of 0.2–0.3 mm at depths in the order of 100 mm.

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Underwater laser triangulation sensor calibration method with refraction

OCEANS 2016 MTS/IEEE Monterey ◽

10.1109/oceans.2016.7761235 ◽

2016 ◽

Cited By ~ 1

Author(s):

Gabriel Matos ◽

Pedro Buschinelli ◽

Tiago Pinto

Keyword(s):

Calibration Method ◽

Sensor Calibration ◽

Laser Triangulation ◽

Underwater Laser ◽

Laser Triangulation Sensor ◽

Triangulation Sensor

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A Multi Camera and Multi Laser Calibration Method for 3D Reconstruction of Revolution Parts

Sensors ◽

10.3390/s21030765 ◽

2021 ◽

Vol 21 (3) ◽

pp. 765

Author(s):

Hugo Álvarez ◽

Marcos Alonso ◽

Jairo R. Sánchez ◽

Alberto Izaguirre

Keyword(s):

3D Reconstruction ◽

Calibration Method ◽

Laser Plane ◽

Calibration Methods ◽

Laser Calibration ◽

Calibration Object ◽

Focus Plane ◽

Chessboard Pattern ◽

Line Patterns

This paper describes a method for calibrating multi camera and multi laser 3D triangulation systems, particularly for those using Scheimpflug adapters. Under this configuration, the focus plane of the camera is located at the laser plane, making it difficult to use traditional calibration methods, such as chessboard pattern-based strategies. Our method uses a conical calibration object whose intersections with the laser planes generate stepped line patterns that can be used to calculate the camera-laser homographies. The calibration object has been designed to calibrate scanners for revolving surfaces, but it can be easily extended to linear setups. The experiments carried out show that the proposed system has a precision of 0.1 mm.

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Visualization of Internal Flow Field of Propeller Fan

Volume 1A, Symposia: Keynotes; Advances in Numerical Modeling for Turbomachinery Flow Optimization; Fluid Machinery; Industrial and Environmental Applications of Fluid Mechanics; Pumping Machinery ◽

10.1115/fedsm2017-69261 ◽

2017 ◽

Author(s):

Takaya Onishi ◽

H. Sato ◽

M. Hayakawa ◽

Y. Kawata

Keyword(s):

Flow Field ◽

High Performance ◽

Laser Light ◽

Internal Flow ◽

Light Sheet ◽

Tip Vortex ◽

Laser Light Sheet ◽

Blade Surface ◽

Similar Tendency ◽

Flow Phenomena

Propeller fans are required not only to have high performance but also to be extremely quiet. The internal flow field of ventilation propeller fans is even more complicated because they usually have a very peculiar configuration with protruding blades upstream. Thus, many kinds of internal vortices yield which cause noise and their cause and countermeasures are needed to be clarified. The purposes of this paper are to visualize the internal flow of the propeller fan from the static and rotating frame of reference. The internal flow visualization measured from the static frame gives approximately the scale of the tip vortex. The visualization from the rotating coordinate system yields a better understanding of the flow phenomena occurring at the specific blade. The experiment is implemented by using a small camera mounted on the shaft of the fan and rotated it to capture the behavior of the vortices using a laser light sheet to irradiate the blade surface. Hence, the flow field of the specific blade could be understood to some extent. The visualized results are compared with the CFD results and these results show a similar tendency about the generation point and developing process of the tip vortex. In addition, it is found that the noise measurement result is relevant to the effect of tip vortex from the visualization result.

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Noncontacting Vibration Measurement Using a Massless Interferometric Accelerometer

Volume 3C: 15th Biennial Conference on Mechanical Vibration and Noise — Vibration Control, Analysis, and Identification ◽

10.1115/detc1995-0721 ◽

1995 ◽

Author(s):

Keyu Li

Keyword(s):

Elevated Temperatures ◽

Laser Light ◽

Vibration Measurement ◽

Object Surface ◽

Out Of Plane ◽

Plates And Shells ◽

Fringe Patterns ◽

Hostile Environments ◽

Derivatives Of ◽

Object Behavior

Abstract An interferometric strain measurement technique is extended to vibration measurements. The technique is based on two micro-indentations placed on an object surface using a combination of diffraction and interference of laser light. Relative displacements between the two indentations and derivatives of in-plane and out-of-plane vibrational displacements are measured by analyzing the phase shift of the interference fringe patterns. The technique can be used to study bending stress and deflection problems in vibrational beams, plates and shells. The displacement derivatives are measured in real time, from which time derivatives or the velocity and acceleration of the displacement derivative as well as vibrational frequency can be determined. The technique has advantages over an accelerometer in that it is noncontacting and does not require attachment of the transducer to the object which could alter the object behavior. In addition, it has many desirable features such as being extremely compact, massless, and applicable to hostile environments such as those associated with production and elevated temperatures.

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On-Orbit Geometric Calibration from the Relative Motion of Stars for Geostationary Cameras

Sensors ◽

10.3390/s21196668 ◽

2021 ◽

Vol 21 (19) ◽

pp. 6668

Author(s):

Linyi Jiang ◽

Xiaoyan Li ◽

Liyuan Li ◽

Lin Yang ◽

Lan Yang ◽

...

Keyword(s):

Relative Motion ◽

Calibration Method ◽

System Structure ◽

Calibration Model ◽

Control Points ◽

Penetration Process ◽

Geometric Calibration ◽

Positioning Errors ◽

Ground Control Points ◽

Motion Transformation

Affected by the vibrations and thermal shocks during launch and the orbit penetration process, the geometric positioning model of the remote sensing cameras measured on the ground will generate a displacement, affecting the geometric accuracy of imagery and requiring recalibration. Conventional methods adopt the ground control points (GCPs) or stars as references for on-orbit geometric calibration. However, inescapable cloud coverage and discontented extraction algorithms make it extremely difficult to collect sufficient high-precision GCPs for modifying the misalignment of the camera, especially for geostationary satellites. Additionally, the number of the observed stars is very likely to be inadequate for calibrating the relative installations of the camera. In terms of the problems above, we propose a novel on-orbit geometric calibration method using the relative motion of stars for geostationary cameras. First, a geometric calibration model is constructed based on the optical system structure. Then, we analyze the relative motion transformation of the observed stars. The stellar trajectory and the auxiliary ephemeris are used to obtain the corresponding object vector for correcting the associated calibration parameters iteratively. Experimental results evaluated on the data of a geostationary experiment satellite demonstrate that the positioning errors corrected by this proposed method can be within ±2.35 pixels. This approach is able to effectively calibrate the camera and improve the positioning accuracy, which avoids the influence of cloud cover and overcomes the great dependence on the number of the observed stars.

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OPTICAL TRIANGULATION ON INSTATIONARY WATER SURFACES

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprsarchives-xli-b5-85-2016 ◽

2016 ◽

Vol XLI-B5 ◽

pp. 85-91

Author(s):

C. Mulsow ◽

H.-G. Maas ◽

B. Hentschel

Keyword(s):

Water Level ◽

Laser Light ◽

Light Sheet ◽

Water Levels ◽

Laser Line ◽

Frame Rate ◽

Measuring System ◽

Optical Triangulation ◽

Dynamic Experiments ◽

Water Surfaces

The measurement of water surfaces is a key task in the field of experimental hydromechanics. Established techniques are usually gauge-based and often come with a large instrumental effort and a limited spatial resolution. The paper shows a photogrammetric alternative based on the well-known laser light sheet projection technique. While the original approach is limited to surfaces with diffuse reflection properties, the developed technique is capable of measuring dynamically on reflecting instationary surfaces. Contrary to the traditional way, the laser line is not observed on the object. Instead, using the properties of water, the laser light is reflected on to a set of staggered vertical planes. The resulting laser line is observed by a camera and measured by subpixel operators. A calibration based on known still water levels provides the parameters for the translation of image space measurements into water level and gradient determination in dynamic experiments. As a side-effect of the principle of measuring the reflected laser line rather than the projected one, the accuracy can be improved by almost a factor two. In experiments a standard deviation of 0.03 mm for water level changes could be achieved. The measuring rate corresponds to the frame rate of the camera. A complete measuring system is currently under development for the Federal Waterways Engineering and Research Institute (BAW). <br><br> This article shows the basic principle, potential and limitations of the method. Furthermore, several system variants optimised for different requirements are presented. Besides the geometrical models of different levels of complexity, system calibration procedures are described too. The applicability of the techniques and their accuracy potential are shown in several practical tests.

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Use of Magnetic Field for Mitigating Gyroscope Errors for Indoor Pedestrian Positioning

Sensors ◽

10.3390/s18082592 ◽

2018 ◽

Vol 18 (8) ◽

pp. 2592 ◽

Cited By ~ 4

Author(s):

Ming Ma ◽

Qian Song ◽

Yang Gu ◽

Zhimin Zhou

Keyword(s):

Magnetic Field ◽

Static Magnetic Field ◽

Inertial Navigation System ◽

Three Dimensional ◽

Calibration Method ◽

Rate Of Change ◽

Superior Performance ◽

Novel Approach ◽

Straight Line ◽

Magnetometer Calibration

In the field of indoor pedestrian positioning, the improved Quasi-Static magnetic Field (iQSF) method has been proposed to estimate gyroscope biases in magnetically perturbed environments. However, this method is only effective when a person walks along straight-line paths. For other curved or more complex path patterns, the iQSF method would fail to detect the quasi-static magnetic field. To address this issue, a novel approach is developed for quasi-static magnetic field detection in foot-mounted Inertial Navigation System. The proposed method detects the quasi-static magnetic field using the rate of change in differences between the magnetically derived heading and the heading derived from gyroscope. In addition, to eliminate the distortions caused by system platforms and shoes, a magnetometer calibration method is developed and the calibration is transformed from three-dimensional to two-dimensional coordinate according to the motion model of a pedestrian. The experimental results demonstrate that the proposed method can provide superior performance in suppressing the heading errors with the comparison to iQSF method.

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Locomotion in scombrid fishes: visualization of flow around the caudal peduncle and finlets of the chub mackerel Scomber japonicus

Journal of Experimental Biology ◽

10.1242/jeb.204.13.2251 ◽

2001 ◽

Vol 204 (13) ◽

pp. 2251-2263 ◽

Cited By ~ 9

Author(s):

Jennifer C. Nauen ◽

George V. Lauder

Keyword(s):

Laser Light ◽

Light Sheet ◽

Flow Speed ◽

The Body ◽

Scomber Japonicus ◽

Laser Light Sheet ◽

Chub Mackerel ◽

Caudal Peduncle ◽

Local Flow ◽

Scombrid Fishes

SUMMARY Scombrid fishes are known for high-performance locomotion; however, few data are available on scombrid locomotor hydrodynamics. In this paper, we present flow visualization data on patterns of water movement over the caudal peduncle and finlets (small fins on the dorsal and ventral body margin anterior to the caudal fin). Chub mackerel, Scomber japonicus, ranging in fork length from 20 to 26 cm, swam steadily at 1.2forklengthss−1 in a recirculating flow tank. Small, reflective particles in the flow tank were illuminated by a vertical (xy) or horizontal (xz) laser light sheet. Patterns of flow in the region near the caudal peduncle were measured using digital particle image velocimetry. Patterns of flow along the peduncle and finlets were quantified using manual particle tracking; more than 800 particles were tracked for at least 12ms over a series of tailbeats from each of four fish. In the vertical plane, flow trajectory and flow speed were independent of the position of the finlets, indicating that the finlets did not redirect flow or affect flow speed. Along, above and below the trailing surface of the peduncle, where the finlets were oriented along the peduncular surface, flow was convergent. Along, above and below the leading surface of the peduncle, where the finlets were absent, the flow trajectory was effectively horizontal. The lack of divergent flow on the leading surface of the peduncle is consistent with cross-peduncular flow formed by the lateral motion of the peduncle interacting with convergent flow resulting from forward movement of the body. In the horizontal plane, particles illuminated by the xz light sheet situated approximately 3 mm below the ventral body surface were tracked within the laser light sheet for up to 40ms, indicating strong planar flow. As the peduncle decelerates, the most posterior finlet is frequently at an angle of attack of at least 20° to the incident flow, but this orientation does not result in thrust production from lift generation. Finlet 5 does redirect cross-peduncular flow and probably generates small vortices undetectable in this study. These data are the first direct demonstration that the finlets have a hydrodynamic effect on local flow during steady swimming.

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