A three-dimensional particle image velocimetry (PIV) system is introduced in this paper. Based on camera array light field technology and Tomographic PIV principle, this system is designed for the measurement of instantaneous or continuous three-dimensional velocity of the flow field section or for the measurement of instantaneous three-dimensional velocity within a volume. The camera array light field technology is capable of collecting four-dimensional light field data, and can flexibly adjust the observation field of view, focus position and depth of field through calculation processing. Therefore, combining the camera array light field technology with the Tomo-PIV a 3-dimensional PIV system is achieved. In this paper, the design and development of the system is presented, experimental results and analysis based on this system are discussed.
Scattering is the fundamental issue in the field of underwater optics, meanwhile polarization state is also a key feature in underwater laser communications, laser imaging, and underwater quantum optical communication. Aiming at this problem, a software package Geant4 is applied in the simulation, furthermore, an algorithm based on the basic Henyey-Greenstein phase functions and typical polarization Monte Carlo model is proposed, the algorithm is used to simulate the polarization state when the laser is propagating underwater at different concentrations of water or transmission length. At the same time, the experiment is tested in a sink whose length is 10m and the polarization state detector is a laser power meter with accuracy up to 10nW. In this paper, the change of polarization state is expressed by the depolarization ratio. The result of numerical simulation and experimental show the variation of polarization state with concentration and distance respectively, the simulation result of Geant4 is more ideal, due to different kinds of external factors the experimental results are roughly, however, the overall change trend of the two is consistent.
The change of quantities and categories of plankton is essential for studying marine ecosystems. For decades development, there has been an accelerating advancement of plankton imaging system. To detect plankton accurately and effectively, the In situ Dark-field Microscope (OUC-IDM) was designed based on the principle of dark-field microscopy, with the purpose of detecting the plankton and macroscopic particles at the range of 100 μm to 10mm. The OUC-IDM is in a position to non-invasively imaging plankton in-situ at nearly micrometer resolution. It is worthwhile to mention that the design of OUC-IDM is more compact, smaller, and lighter than its predecessor, not only that, both cameras and embedded computers have been upgraded. Furthermore, Full-color information of plankton can be obtained by using a high-power white color LED as light source, which is favorable for identification of plankton in the advanced stage. To validate the usefulness of the OUC-IDM, the instrument was deployed along the coast in Qingdao several times, colorful and vividly in-situ images have been taken and directly used without or with sample image post-processing. Have regard to the functional differences, the OUC-IDM is best employed to complement rather than replace traditional studying.
Three-dimensional terrain data have a wide range of applications in urban planning, environmental monitoring, disaster prediction, game entertainment and many other fields. With the development of science and technology and the progress of cognitive psychology, displaying technology has also been improved to fulfill the demand of humans, and promotes the rapid development of three-dimensional display technology. Nowadays, the visualization technology of three-dimensional terrain is a research hotspot in related fields. Through the terrain data model building, simulation and three-dimensional displaying, a variety of techniques have been used to achieve the display of three-dimensional terrain. The three-dimensional display is a technique for displaying three-dimensional images with the medium of two-dimensional plane, which can visually present the different angles and depth information of object and bring the realism close to the objective world. The effect is very similar to people's visual and cognitive habits, which makes it accepted as an ideal real three-dimensional display technology. How to realize the visualization of 3D terrain data without any special glasses or relying on electronic display devices is the research topic of this paper. In this paper, a method of combining Fourier holography with full parallax holographic stereogram is presented to realize the display of three-dimensional terrain by making full parallax hologram. Firstly, the SRTM terrain (elevation) data is processed, the three-dimensional digital model of terrain is established and then is sampled according to the principle of holographic stereogram, and thus a two-dimensional image array containing parallax information is obtained. Then, according to the holographic diffraction formula, the image transformation of two-dimensional image array is carried out to meets the requirement of Fourier holographic transform. Finally, the holographic recording optics setup is designed and the following procedures are take: laser beam is divided into object beam and reference beam, Fourier transform are involved in the procession of object beam, interference between the reference light beam and the Fourier transform image is recorded in the focus point of the objective lens, a microscopic objective with large NA is used to achieve enough view angle, images need to be recorded are displayed one at a time by a LCOS light modulator, under the position of the precision platform every unit of the hologram is recorded automatically, precisely and effectively. After post - processing, the three-dimensional topographic hologram with large view field and full parallax are accomplished. The method presented in this paper realizes the efficient automatic production of three-dimensional topographic hologram based on SRTM terrain data. Under the white light illumination, using the large-view-field and full-parallax three-dimensional hologram display, the elevation data of the terrain are displayed intuitively, accurately, clearly and delicately, which is of great significance for the research of high quality and large field holographic three-dimensional display, and has practical application value in Landform Surveying, commodity exhibition, anti-counterfeiting, advertising and so on.
Light Field camera is a kind of device which uses a microlens array to record the four-dimensional light field information in the scene and matches the light with the CCD to realize the function of image refocusing according to given relationship. In this paper, we apply the microlens array in the underwater microscopy system and use microscopic objective, microlens array and CCD to construct an underwater light field microscope. We improve microscopy system which has small depth and is difficult to focus and evaluate effect of microlens array on light field sampling and resolution of refocused images at different positions. In the experiments, we calibrate camera, confirm the magnification and field size and take some photos of marine plankton in the experimental environment.
Aiming at being carried on various underwater vehicles for the detection of plankton, a miniaturized in-situ digital inline holographic system named OUC-HoloCam200 is designed and developed. Although the structure of OUC-HoloCam200 is simple and compact, the system performance is still excellent. Tests have been carried out and the result shows that the optical resolution of OUC-HoloCam200 is 8.77 μm, the depth of field is up to 30 cm, the field of view is 8.44×6.75 mm2 , which means theoretically with each exposure, about 300 mL of seawater can be investigated. OUC-HoloCam200 have been deployed in the nearshore area of the South China Sea and have worked continuously over 48 hours, after holographic reproduction and image processing the data is able to show the trends of changing in number and species of plankton over time in the same location.
Plankton is an important part of the marine life, which plays a significant role in studying the change of global climate and the marine ecological environment. In order to detect plankton accurately and effectively, we design the Underwater In-situ Dark-field Microscopy Detection System based on the principle of dark-field microscopy. The experiment results show that while the 2× microscope objective is used, the resolution is 90.5lp/mm and the horizontal field of view is 2.6×2.6mm and while the 10× microscope objective is used, the resolution is 181lp/mm and the horizontal field of view is 2.2×2.2mm, when the microscope objective is replaced by 0.9× large format telecentric lens, the detection area will be 11mm with the resolution of 32lp/mm. Double compartment structure is designed, such that the system can work underwater.
This paper proposes a new method for three-dimensional dynamic holographic display that combines computer
generated holography (CGH) and holographic stereogram. Theoretically, three-dimensional (3D) dynamic holographic
display can be achieved by using CGH alone, however the application of CGH is still limited because large amounts of
data processing and complex mathematical calculation of off-axis diffracted light field. A new method combining CGH
and stereogram is proposed, since stereogram uses a set of 2D images instead of a 3D object, both the complexity of the
calculation and the resolution requirements of spatial light modulator (SLM) is reduced. To prove the feasibility of this
method, experiments of making hologram using this method is carried out and the result shows that 3D displaying with a
view angle of 28 is achieved.
Due to the absorption and scattering of water, images acquired in underwater environment have different colors from
those in air, which can cause problem for image processing and object recognition. Addressing the problem of color
correction, this paper presents a method of color restoration based on water absorption spectrum. Considering the
nonlinear attenuate of light in different wavelength at different depths, the changes of tri-stimulus values are calculated.
Experiments are carried out in coastal seawater. The change of tri-stimulus values are used to compensate color loss. The
results demonstrate the feasibility of our method.
This paper presents a novel synthetic generated hologram (SGH) system, in which a digital micromirror device (DMD) is used as space light modulator (SLM). In the system, the object light beam is directed through a sequence of digital images on a space light modulator, digital micromirror device (DMD), rather than the transparent films used in the conventional SGH. A computer controlled distributing device replace manual operation. With this system, threedimensional full color hologram can be generated by synthesizing a series of two-dimension digital images, obtained by digital camera or generated by computer software. The preliminary experimental results have been obtained with this system. The possible future development has also been discussed.