This work studies the application of laser structured light scanning to measure the small scale roughness of seabed. We use a CCD camera to capture the dislocation of laser light. The location of the laser light in pixel coordinates can be converted into world coordinates if the CCD camera is calibrated. We propose an algorithm which is analogous to the idea of longitudes/latitudes in map projection. The idea is to place a calibration board to be aligned with the laser scanning sheet. On the calibration board, grid points of 50mm are laid to represent the intersection of the longitudes and latitudes. The position of a point in pixel coordinates can be obtained by referring to its neighboring graticule. We designed three experiments to verify the accuracy of the system: The first experiment consists of measuring the distance between feature points on the calibration board, then check and correct the optic distortion effects of the lenses. The second experiment is to measure the slice of laser scanning image of a known object, and check the accuracy of our laser scanning system by measuring the object's height and width. In the third experiment, we measure an object which has a small height variety of its surface, to test the resolution of the system. The results indicate that the error is under 1%, only then that we proceed with the design, analysis, and measurement of artificial seabed. The artificial seabed model is made by using a 210mm * 210mm * 30mm acrylic board with sand ripples forms in the 150mm * 150mm square. The amplitude of the ripples is no higher/larger than ¡Ó 8mm, and no lower/smaller than ¡Ó 1.5mm. Contour map of the sand ripples would be plotted to analyze the results obtained from the measurements. The analysis is carried out by obtaining slice data from a reconstructed surface of the sand ripples, then compare it with the theoretical values. From the result we know that the error between sand dune ideal wave index and measured index is in the range of ¡Ó 2mm. To further test the system's tolerance with turbidity, we incorporate conditions which would alter environmental turbidity into the seabed experiments before running the experiments for analysis. The results show that the system is able to maintain a stable performance in an environment below 2.3 NTU (Nephelometric Turbidity Unit), and the error between ideal sand dune ideal wave index and measured index is still in the range of ¡Ó 2mm.

This paper reports the design and development of an underwater laser scanning system to measure the geometry of underwater objects. The application of structure light scanning method requires a calibrated CCD camera as the input device. Because the underwater environment is by far different from that in the air. Conventional calibration methods adopted in the air can not be applied for the underwater cases. In this paper we propose an algorithm which is analogous to the idea of longitudes/latitude in map projection to calibration the CCD. The calibration board pattern is fabricated by laying vertical and horizontal grid dots of 5cm span with an NC milling machine. To obtain the higher accuracy, we redesign the laser source holder to make the board and laser scan line coplane. We use a new laser that is focus adjustable. So we can capture clearer image of the edge on the target. Then, we calibrate the CCD camera with the calibration board. For testing our new system, two test pieces are used. One is sine waves ripples with varying amplitudes from 8mm to 3 mm. The other one is a rough surface with know spatial power spectrum. Scanning results show that: Scanning from rough 1 meter away, the absolute error for the sine wave ripples is less than 1mm along vertical direction. The power spectrum for the rough surface is accurate to the order of 3 to 5mm wave number. In order to survive in the harsh underwater environment, we design and make a rotational scanning system. The system was designed as an automatic image-capturing system, utilizing single board computer as control plane to work in conjunction with PLC(Programmable Logic Controller) for System power management. When using two 12V batteries as main power source, obtaining samples once per hour, capturing 360 images per operation, the system may run for approximately 39 hours.

This work reports the system integration of the underwater seafloor laser scanner, designed and fabricated by Institute of Undersea Technology, National Sun Yat-sen University, with the in situ porosity measurement system, known as IMP2, developed by Applied Physics Lab, University of Washington. Our original prototype underwater seafloor laser scanner worked more like an indoor experimental setup rather than an instrument. It is the goal of this work to modify the detail design of hardware and software of the system such that the operation of the scanner and the data analysis of the results can be done like a commercial instrument. Our laser scanning module adopts structural light method with a single camera approach. The calibration of the camera is achieved with a template board on which sets of grid points are laid with numerical control milling machine. These grid points are used to create longitudinal and latitudinal lines for pixel-to-coordinate conversion. Three sub-pixel sampling methods, namely, intensity weighted centroid, second order polynomial intensity fitting and Gaussian intensity fitting, are developed to locate the center of the laser light strip on pixel plane and to be converted into engineering coordinates. For the convenience of post-processing, grid point meshing and spectrum analysis packages are built-in to provide standard output for further studies. The overall performance of the system was validated by four tests in indoor tanks and field as well. One scanning in air was undertaken to verify if synchronization signal between the laser scanner and the motion of the linear track was correct; several models of known dimension were placed in the water tank for scanning to see if the system reaches the desired accuracy; an integration of the laser scanner and the IMP2 was tested prior to the deployment in the sea, and a scanning a artificial seafloor model of known spatial spectra indicated the proper functioning of the combined system; finally a successful 20-meter deep field deployment and retrieve assured the bases for the acquisition of seafloor roughness field for acoustics related research.

This master thesis has been performed by request of Dekra Industrial AB. Dekra Industrial AB is a Swedish subsidiary company of the German company Dekra and works for example with safety inspections within the nuclear power industry. The inspections performed by the company are often non-destructive testing (NDT) such as visual inspections of nuclear reactor pressure vessels. The inspection methods used today are considered to be further developed and there is a strong demand of improving the visual inspection. 3D-Imaging techniques are starting to be used as a measuring tool within the industry and could be a potential aid tool for the visual inspection. The purpose with the master thesis is to gain an understanding of 3D-Imaging technique to propose a suitable implementation so that it may be used as an aid tool for visual inspection. The main goal with the master thesis work is to gain knowledge about 3D-Imaging techniques and propose an implementation which may be used in the nuclear power industry. However there are different types of techniques and all of them have advantages and disadvantages. The method began with a comprehensive study about 3D-Imaging techniques, optics of 3D-Imaging and behaviour of electronics in radioactive environment. Information that could not be acquired by literature alone is acquired by interviews and meetings. The chosen 3D-Imaging technique that was considered to be the most suitable was structural light. Structural light is built on a triangulation principle that uses a projector and a camera for acquiring 3D coordinates. By using patterns displayed by the projector onto the object the camera may detect the reflected patterns and thus creating 3D coordinates. A structural light system was built and tested. The main test consisted about a two-level factorial design. The tested factors were triangulation angle, brightness and measurement distance. The test run that had the largest triangulation angle, highest brightness and shortest measurement distance gave the best accuracy. The accuracy was determined by measuring the flatness of the object. The best accuracy was measured to 91.5 μm. Besides the accuracy the technique has proven its potential by being able to scan weld tests and reconstruct well defined point clouds of the weld profiles. In conclusion the goal of the master thesis was reached and the demanded accuracy was reached. The accuracy is comparable with some industrial systems available today. This was possible due to use of a high resolution still camera. Since the camera and projector are commercially available products the tests proves that there is room for further improvements in order to reach better and a more robust accuracy. Keywords: Dekra Industrial AB, Visual testing, Imaging technique, Structural light / Detta examensarbete har utförts på uppdrag av Dekra Industrial AB. Dekra Industrial AB är ett dotterbolag till Dekra. Dekra Industrial AB arbetar främst med kontroller och provningar inom industrin. Kärnkraftindustrin är en industrigren där DEKRA arbetar med sådan kontroll Inspektionerna som utförs består huvudsakligen av oförstörande provning såsom visuell provning. Metoderna som används idag behöver vidareutvecklas och det finns en stark efterfrågan att förbättra den visuella inspektionen. 3D-avbildningsteknik är allt vanligare inom industrin idag och skulle kunna användas som ett mäthjälpmedel för att komplettera den visuella inspektionen. Syftet med examensarbetet är att få en förståelse för hur väl tekniken fungerar samt att föreslå en tillämpning där den kan komma att användas som ett komplement till den visuella inspektionen. Målet med arbetet är att ta fram underlag och föreslå en tillämpning för provning i högstrålande miljö. 3D-avbildningsteknik är ett generellt namn för många olika typer av tekniker som har sina fördelar respektive nackdelar. Arbetet inleds med en litteraturstudie kring 3D-avbildningstekniker, fysik med avseende på avbildningsteknik, den visuella proceduren idag samt hur elektronik påverkas av högstrålande miljö. Information som inte kan fås via studier inhämtas via intervjuer och möten. Tekniken som valdes att analyseras var strukturerat ljus. Tekniken bygger på en trianguleringsprincip som använder en projektor och kamera för att tillförskaffa 3D-koordinater. Genom att projicera mönster på ett objekt kan kameran detektera det reflekterade mönstret och på så vis skapa 3D koordinater. Ett strukturerat ljus system ställdes upp och testades. Testet bestod huvudsakligen av en försöksplanering där de testade faktorerna var trianguleringsvinkel, ljusstyrka och mätavstånd. Testuppställningen som gav bäst resultat var med störst trianguleringsvinkel, högsta ljusstyrka samt kortast mätavstånd. Noggrannheten bestämdes genom att mäta planheten på objektet. Den bästa noggrannheten som uppnåddes med testet var 91.5 μm. Förutom den goda noggrannheten har tekniken visat sin potential genom att avbilda ett svetsprov som genererade ett väldefinierat punktmoln av svetsprofilen. Sammanfattningsvis uppfylldes målen och det uppställda systemet gav en noggrannhet som är jämförbar med en del system ute på marknaden. Detta var möjligt på grund av att en högupplöst stillbildskamera användes. Det finns potential för förbättringar då komponenterna som används i systemet är kommersiella produkter. Nyckelord: Dekra Industrial AB, Visuell inspektion, Avbildningsteknik, Strukturerat ljus