Spatial and temporal phase-measurement techniques: a comparison of major error sources in one dimension

1993 ◽  
Author(s):  
Joanna Schmit ◽  
Katherine Creath ◽  
Malgorzata Kujawinska
Keyword(s):  
Phase Measurement ◽  
Measurement Techniques ◽  
One Dimension ◽  
Major Error ◽  
Error Sources ◽  
Temporal Phase

scholarly journals High-Quality Pixel Selection Applied for Natural Scenes in GB-SAR Interferometry

2021 ◽  
Vol 13 (9) ◽  
pp. 1617
Author(s):  
Yunkai Deng ◽  
Weiming Tian ◽  
Ting Xiao ◽  
Cheng Hu ◽  
Hong Yang
Keyword(s):  
Phase Measurement ◽  
High Amplitude ◽  
Sar Interferometry ◽  
Spatial Density ◽  
Natural Scenes ◽  
Sar Images ◽  
High Quality ◽  
Temporal Phase ◽  
Permanent Scatterers ◽  
High Phase

Phase analysis based on high-quality pixel (HQP) is crucial to ensure the measurement accuracy of ground-based SAR (GB-SAR). The amplitude dispersion (ADI) criterion has been widely applied to identify pixels with high amplitude stability, i.e., permanent scatterers (PSs), which typically are point-wise scatterers such as stones or man-made structures. However, the PS number in natural scenes is few and limits the GB-SAR applications. This paper proposes an improved method to take HQP selection applied for natural scenes in GB-SAR interferometry. In order to increase the spatial density of HQP for phase measurement, three types of HQPs including PS, quasi-permanent scatter (QPS), and distributed scatter (DS), are selected with different criteria. The ADI method is firstly utilized to take PS selection. To select those pixels with high phase stability but moderate amplitude stability, the temporal phase coherence (TPC) is defined. Those pixels with moderate ADI values and high TPC are selected as QPSs. Then the feasibility of the DS technique is explored. To validate the feasibility of the proposed method, 2370 GB-SAR images of a natural slope are processed. Experimental results prove that the HQP number could be significantly increased while slightly sacrificing phase quality.

scholarly journals Single image geometry inspection using inverse endoscopic fringe projection

ACTA IMEKO ◽  
2015 ◽  
Vol 4 (2) ◽  
pp. 4 ◽  
Author(s):  
Steffen Matthias ◽  
Christoph Ohrt ◽  
Andreas Pösch ◽  
Markus Kästner ◽  
Eduard Reithmeier
Keyword(s):  
Phase Measurement ◽  
Measurement Techniques ◽  
Measuring Method ◽  
Pattern Generation ◽  
Fringe Projection ◽  
Free Form ◽  
Projection System ◽  
New Device ◽  
Early Results ◽  
Geometry Inspection

Fringe projection is an important technology for the measurement of free form elements in several application fields. It can be applied for geometry elements smaller than one millimeter. In combination with deviation analysis algorithms, errors in fabrication lines can be found promptly to minimize rejections. However, some fields cannot be covered by the classical fringe projection approach. Due to shadowing, filigree form elements on narrow or internal carrier geometries cannot be captured. To overcome this limitation, a fiberscopic micro fringe projection sensor was developed. The new device is capable of resolutions of less than 15 µm with uncertainties of about 35 µm in a workspace of 3 × 3 × 3 mm³.<br />Using standard phase measurement techniques, such as Gray-code and cos²-patterns, measurement times of over a second are too high for in-situ operation. The following work will introduce a new approach of applying a new one image measuring method to the fiberscopic system, based on inverse fringe projection. The fiberscopic fringe projection system employs a laser light source in combination with a digital micro-mirror device (DMD) to generate fringe patterns. Fiber optical image bundles (FOIB) are used in combination with gradient-index lenses to project these patterns on the specimen. This advanced optical system creates high demands on the pattern generation algorithms to generate exact inverse patterns for arbitrary CAD-modelled geometries. Approaches of the optical simulations in the context of the complex beam path, together the drawbacks of the limited resolutions of the FOIBs shall be discussed. Early results of inverse pattern simulations using a ray tracing approach of a pinhole system model are presented.<br />

scholarly journals Temporal phase unwrapping using deep learning

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Wei Yin ◽  
Qian Chen ◽  
Shijie Feng ◽  
Tianyang Tao ◽  
Lei Huang ◽  
...  
Keyword(s):  
Machine Learning ◽  
Deep Learning ◽  
High Frequency ◽  
Phase Unwrapping ◽  
Motion Artifacts ◽  
Error Sources ◽  
Actual Measurement ◽  
Temporal Phase ◽  
Fringe Patterns ◽  
Frequency Phase

AbstractThe multi-frequency temporal phase unwrapping (MF-TPU) method, as a classical phase unwrapping algorithm for fringe projection techniques, has the ability to eliminate the phase ambiguities even while measuring spatially isolated scenes or the objects with discontinuous surfaces. For the simplest and most efficient case in MF-TPU, two groups of phase-shifting fringe patterns with different frequencies are used: the high-frequency one is applied for 3D reconstruction of the tested object and the unit-frequency one is used to assist phase unwrapping for the wrapped phase with high frequency. The final measurement precision or sensitivity is determined by the number of fringes used within the high-frequency pattern, under the precondition that its absolute phase can be successfully recovered without any fringe order errors. However, due to the non-negligible noises and other error sources in actual measurement, the frequency of the high-frequency fringes is generally restricted to about 16, resulting in limited measurement accuracy. On the other hand, using additional intermediate sets of fringe patterns can unwrap the phase with higher frequency, but at the expense of a prolonged pattern sequence. With recent developments and advancements of machine learning for computer vision and computational imaging, it can be demonstrated in this work that deep learning techniques can automatically realize TPU through supervised learning, as called deep learning-based temporal phase unwrapping (DL-TPU), which can substantially improve the unwrapping reliability compared with MF-TPU even under different types of error sources, e.g., intensity noise, low fringe modulation, projector nonlinearity, and motion artifacts. Furthermore, as far as we know, our method was demonstrated experimentally that the high-frequency phase with 64 periods can be directly and reliably unwrapped from one unit-frequency phase using DL-TPU. These results highlight that challenging issues in optical metrology can be potentially overcome through machine learning, opening new avenues to design powerful and extremely accurate high-speed 3D imaging systems ubiquitous in nowadays science, industry, and multimedia.

scholarly journals Transparent Object Shape Measurement Based on Deflectometry

Proceedings ◽  
2018 ◽  
Vol 2 (8) ◽  
pp. 548
Author(s):  
Zhichao Hao ◽  
Yuankun Liu
Keyword(s):  
Data Acquisition ◽  
Phase Measurement ◽  
Focal Length ◽  
Three Dimensional ◽  
Normal Direction ◽  
Calibration Data ◽  
Actual Measurement ◽  
Temporal Phase ◽  
Convex Lens ◽  
Normal Orientation

This paper proposes a method for obtaining surface normal orientation and 3-D shape of plano-convex lens using refraction stereo. We show that two viewpoints are sufficient to solve this problem under the condition that the refractive index of the object is known. What we need to know is that (1) an accurate function that maps each pixel to the refraction point caused by the refraction of the object. (2) light is refracted only once. In the simulation, the actual measurement process is simplified: light is refracted only once; and the accurate one-to-one correspondence between incident ray and refractive ray is realized by known object points. The deformed grating caused by refraction point is also constructed in the process of simulation. A plano-convex lens with a focal length of 242.8571 mm is used for stereo data acquisition, normal direction acquisition, and the judgment of normal direction consistency. Finally, restoring the three-dimensional information of the plano-convex lens by computer simulation. Simulation results suggest that our method is feasibility. In the actual experiment, considering the case of light is refracted more than once, combining the calibration data acquisition based on phase measurement, phase-shifting and temporal phase-unwrapping techniques to complete (1) calibrating the corresponding position relationship between the monitor and the camera (2) matching incident ray and refractive ray.

scholarly journals Wavefront measurement techniques used in high power lasers

2014 ◽  
Vol 2 ◽  
Author(s):  
Haiyan Wang ◽  
Cheng Liu ◽  
Xiaoliang He ◽  
Xingchen Pan ◽  
Shenlei Zhou ◽  
...  
Keyword(s):  
High Power ◽  
Phase Measurement ◽  
Measurement Techniques ◽  
Wavefront Sensor ◽  
Power Laser ◽  
Laser Applications ◽  
High Power Lasers ◽  
Coherent Diffraction Imaging ◽  
Wavefront Measurement ◽  
Diffraction Imaging

AbstractThe properties of a series of phase measurement techniques, including interferometry, the Hartmann–Shack wavefront sensor, the knife-edge technique, and coherent diffraction imaging, are summarized and their performance in high power laser applications is compared. The advantages, disadvantages, and application ranges of each technique are discussed.

scholarly journals Spectral and temporal phase measurement by optical frequency-domain reflectometry

2014 ◽  
Author(s):  
Bruno Robillart ◽  
Cosimo Calò ◽  
Abdoulaye Fall ◽  
François Lamare ◽  
Yaneck Gottesman ◽  
...  
Keyword(s):  
Frequency Domain ◽  
Phase Measurement ◽  
Optical Frequency ◽  
Temporal Phase ◽  
Optical Frequency Domain Reflectometry ◽  
Frequency Domain Reflectometry
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