scholarly journals A Robust InSAR Phase Unwrapping Method via Phase Gradient Estimation Network

2021 ◽  
Vol 13 (22) ◽  
pp. 4564
Author(s):  
Liming Pu ◽  
Xiaoling Zhang ◽  
Zenan Zhou ◽  
Liang Li ◽  
Liming Zhou ◽  
...  

Phase unwrapping is a critical step in synthetic aperture radar interferometry (InSAR) data processing chains. In almost all phase unwrapping methods, estimating the phase gradient according to the phase continuity assumption (PGE-PCA) is an essential step. The phase continuity assumption is not always satisfied due to the presence of noise and abrupt terrain changes; therefore, it is difficult to get the correct phase gradient. In this paper, we propose a robust least squares phase unwrapping method that works via a phase gradient estimation network based on the encoder–decoder architecture (PGENet) for InSAR. In this method, from a large number of wrapped phase images with topography features and different levels of noise, the deep convolutional neural network can learn global phase features and the phase gradient between adjacent pixels, so a more accurate and robust phase gradient can be predicted than that obtained by PGE-PCA. To get the phase unwrapping result, we use the traditional least squares solver to minimize the difference between the gradient obtained by PGENet and the gradient of the unwrapped phase. Experiments on simulated and real InSAR data demonstrated that the proposed method outperforms the other five well-established phase unwrapping methods and is robust to noise.

2011 ◽  
Vol 105-107 ◽  
pp. 1876-1879
Author(s):  
Wei Ke Liu ◽  
Gou Lin Liu ◽  
Xiao Qing Zhang

The phase of complex signals is wrapped since it can only be measured modulo-2; unwrapping searches for the 2-combinations that minimize the discontinuity of the unwrapped phase, as only the unwrapped phase can be analyzed and interpreted by further processing. Weighted least squares phase unwrapping algorithm could avoid errors transmission in the whole phase images, but it could not avoid defect and overlay of interference fringes caused by topographic factors. Therefore, a new phase unwrapping and weights choosing method based on local phase frequency estimate of topographic factors was presented. Experiments show it is an efficient phase unwrapping method which well overcome the defect of under-estimate slopes by least squares algorithm, and has higher accuracy and stability than other methods.


2017 ◽  
Vol 53 (10) ◽  
pp. 683-685 ◽  
Author(s):  
Tao Zhang ◽  
Xiaolei Lv ◽  
Jiang Qian ◽  
Jun Hong ◽  
Ye Yun

2020 ◽  
Vol 10 (1) ◽  
pp. 53-61
Author(s):  
E. Mysen

AbstractA network of pointwise available height anomalies, derived from levelling and GPS observations, can be densified by adjusting a gravimetric quasigeoid using least-squares collocation. The resulting type of Corrector Surface Model (CSM) is applied by Norwegian surveyors to convert ellipsoidal heights to normal heights expressed in the official height system NN2000. In this work, the uncertainty related to the use of a CSM to predict differences in height anomaly was sought. As previously, the application of variograms to determine the local statistical properties of the adopted collocation model led to predictions that were consistent with their computed uncertainties. For the purpose of predicting height anomaly differences, the effect of collocation was seen to be moderate in general for the small spatial separations considered (< 10 km). However, the relative impact of collocation could be appreciable, and increasing with distance, near the network. At last, it was argued that conservative uncertainties of height anomaly differences may be obtained by rescaling output of a grid interpolation by \sqrt \Delta, where Δ is the spatial separation of the two locations for which the difference is sought.


Author(s):  
Katsumasa Miyazaki ◽  
Kunio Hasegawa ◽  
Koichi Saito

The fitness-for-service codes require the characterization of non-aligned multiple flaws for flaw evaluation, which is performed using a flaw proximity rule. Worldwide, almost all such codes provide their own proximity rule, often with unclear technical bases of the application of proximity rule to ductile or fully plastic fracture. In particular, the effect of flaw dimensions of multiple surface flaws on fully plastic fracture of non-aligned multiple flaws had not been clear. To clarify the effect of the difference of part through-wall and through-wall flaws on the behavior of fully plastic fracture, the fracture tests of flat plate specimens with non-aligned multiple part through-wall flaws were conducted. When the flaw depth a was shallow with 0.4 in ratio of a to thickness t, the maximum load Pmax occurred at penetration of multiple flaws and the effect of vertical distance of non-aligned multiple flaws H on Pmax was not so significant. However, when flaw depth was deep with 0.8 in a/t, Pmax occurred after penetration of flaws and the effect of H on Pmax could be seen clearly. It was judged that the through-wall flaw tests were appropriate for discussion of the effect of H on Pmax and the alignment rule of multiple flaws. In addition, in order to clarify the appropriate length parameter to estimate Pmax of test specimens with dissimilar non-aligned through-wall multiple flaws, the fracture tests of plate specimens were also conducted. The effect of different flaw length on Pmax was discussed with maximum, minimum and averages of dissimilar non-aligned multiple flaw lengths. Experimental results showed that the maximum length lmax would be an appropriate length parameter to estimate Pmax, when the non-aligned multiple through-wall flaws were dissimilar.


2012 ◽  
Vol 6-7 ◽  
pp. 76-81
Author(s):  
Yong Liu ◽  
Ding Fa Huang ◽  
Yong Jiang

Phase-shifting interferometry on structured light projection is widely used in 3-D surface measurement. An investigation shows that least-squares fitting can significantly decrease random error by incorporating data from the intermediate phase values, but it cannot completely eliminate nonlinear error. This paper proposes an error-reduction method based on double three-step phase-shifting algorithm and least-squares fitting, and applies it on the temporal phase unwrapping algorithm using three-frequency heterodyne principle. Theoretical analyses and experiment results show that this method can greatly save data acquisition time and improve the precision.


2018 ◽  
Vol 63 (05) ◽  
pp. 1385-1403 ◽  
Author(s):  
KITAE SOHN ◽  
ILLOONG KWON

Trust was found to promote entrepreneurship in the US. We investigated whether this was true in a developing country, Indonesia. We failed to replicate this; this failure was true whether trust was estimated at the individual or community level or whether ordinary least squares (OLS) or two stage least squares (2SLS) was employed. We reconciled the difference between our results and those for the US by arguing that the weak enforcement of property rights in developing countries and the consequent hold-up problem make it more efficient for entrepreneurs to produce generic goods than relationship-specific goods—producing generic goods does not depend on trust.


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