Comparative research and its significance of deformation measurements by technologies of laser real-time holographic interferome-try and radar differential interferometry

The principles and applications of laser real-time holographic interferometry （LRTHI） and radar differential interferometry （RDI） technologies are described in this paper, respectively. By using LRTHI, we can observe the deformation of samples under pressure in the lab and study the anomaly characteristics relating to different strain fields in different fracture-developing areas; while by using RDI, we can observe the landform and surface deformation. The results of deformation observed before and after the Ms=7.9 Mani earthquake （Tibet） and Ms=6.2 Shangyi-Zhangbei earthquake in China are obtained. It is pointed out that LRTHI and RDi are similar, which study the characteristics of anomalous deformation field by fringe variations for both of them. Therefore, the observation of deformation field in the seismogenic process, especially in the period impending an earthquake by RDI, and the comparative study in the lab by LRTHI are of great significance.

Method for differential phase delay resolution of phase referencing VLBI technique and its experimental verification

The phase referencing Very Long Baseline Interferometry(VLBI)technique is a newly developed tool to measure the angular position of a deep space exploration probe in the plane-of-the-sky.Through alternating observations between the probe and a nearby reference radio source,their accurate relative angular separation can be obtained from the radio images generated by this technique.To meet the requirements of the current orbit determination software,differential delay should be firstly derived from those radio images.A method to resolve the differential phase delay from the phase referencing VLBI technique is proposed in this paper,and as well the mathematical model for differential phase ambiguity resolution is established.This method is verified with practical measurement data from the Chang’E-3 mission.The differential phase delay between the Chang’E-3 lander and rover was derived from the phase referencing VLBI measurements,and was then imported into the Shanghai astronomical observatory Orbit Determination Program(SODP)to calculate the position of the rover relative to the lander on the lunar surface.The results are consistent with those acquired directly from radio images,indicating that the differential phase ambiguity has been correctly resolved.The proposed method can be used to promote applications of the phase referencing VLBI technique in future lunar or deep space explorations,and more accurate orbit determination becomes promising.

A new method for resolving phase ambiguity in radio interferometry using Earth rotation synthesis

As a key technique in deep space navigation, radio interferometry can be used to determine the accurate location of a spacecraft in the plane-of-sky by measuring its signal propagation time delay between two remote stations. To improve the measurement accuracy, differential phase delay without phase ambiguity is usually desired. Aiming at the difficulties of resolving phase ambiguity with few stations and narrowband downlink signals, a new method is proposed in this work by taking advantage of the Earth rotation. The high accurate differential phase delay between the spacecraft and a calibrator can be achieved not only in the in-beam observation mode but also in the out-of-beam observation mode. In this paper we firstly built the model of phase ambiguity resolution. Then, main measurement errors of the model are analyzed, which is followed by tests and validations of the model and method using the tracking data of the Cassini mission and Chang'E-3 mission. The results show that the phase ambiguities can be correctly resolved to generate a 10-picosecond level accuracy differential phase delay. Angular measurement accuracy of the Cassini reaches the milli-arc-second level, and the relative position accuracy between the Chang'E-3 rover and lander reaches the meter level.

Homomorphic partial differential equation filtering method for electronic speckle pattern interferometry fringes based on fringe density

Noise reduction is one of the most exciting problems in electronic speckle pattern interferometry. We present a homomorphic partial differential equation filtering method for interferometry fringe patterns. The diffusion speed of the equation is determined based on the fringe density. We test the new method on the computer-simulated fringe pattern and experimentally obtain the fringe pattern, and evaluate its filtering performance. The qualitative and quantitative analysis shows that this technique can filter off the additive and multiplicative noise of the fringe patterns effectively, and avoid blurring high-density fringe. It is more capable of improving the quality of fringe patterns than the classical filtering methods.

同步轨道共位卫星差分CEI测量技术

同步轨道卫星共位是指在一个地球同步轨道±0.1°的窗口上放置2颗或2颗以上的卫星。文章介绍了同步轨道卫星多星共位的必要性和差分连接端站干涉测量的原理,对同步轨道共位卫星位置测量精度进行分析,得出结论:差分连接端站干涉测量技术能够满足同步轨道共位卫星位置测量的要求。

Optimum selection of common master image for ground deformation monitoring based on PS-DInSAR technique

Considering the joint effects of various factors such as temporal baseline, spatial baseline, thermal noise, the difference of Doppler centroid frequency and the error of data processing on the interference correlation, an optimum selection method of common master images for ground deformation monitoring based on the permanent scatterer and differential SAR interferometry （PS-DInSAR） technique is proposed, in which the joint correlation coeficient is used as the evaluation function. The principle and realization method of PS-DInSAR technology is introduced, the factors affecting the DInSAR correlation are analysed, and the joint correlation function model and its solution are presented. Finally an experiment for the optimum selection of common master images is performed by using 25 SAR images over Shanghai taken by the ERS-1/2 as test data. The results indicate that the optimum selection method for PS-DInSAR common master images is effective and reliable.

KEY TECHNOLOGY OF D-INSAR AT X-BAND FOR MONITORING LAND SUBSIDENCE IN MINING AREA AND ITS APPLICATION

In theory, land subsidence measurement results with high accuracy can be obtained by using the Differential Interferometry Synthetic Aperture Radar(D-InSAR) at X-band. In practice, however, the measuring accuracy of D-InSAR at X-band has been seriously affected by some factors, e.g., decorrelation and high deformation gradient. In this work, the monitoring capability of D-InSAR for coal-mining subsidence is evaluated by using SAR data acquired by TerrraSAR-X system. The SAR image registration method for low coherence image pairs, the denoising phase filter for high noise level interferogram and atmospheric effects mitigation method are the key technical aspects which directly influence the measurement results of D-InSAR at X-band. Thus, a robust image registration method, an improved phase filter method and an atmospheric effects mitigation method are proposed in this paper. The proposed image registration method successfully achieves InSAR coregistration, while the amplitude cross-correlation cannot properly coregister low coherence SAR image pairs. Moreover, the time complexity of the proposed image registration method is obviously slighter than that of the Singular Value Decomposition(SVD) method. The comparing experiment results and the unwrapping phase results show that the improved Goldstein filter is more effective than the original Goldstein filter in noise elimination. The atmospheric influence correction experiment results show that the land subsidence areas with atmospheric influence correction are more clarified than that of without atmospheric influence correction. In summary, the presented methods directly improved the measurement results of D-InSAR at X-band.

Characteristics of Unsteady Boundary Layer Induced by the Compression Wave Propagating in a Tunnel

A compression wave is generated ahead of a high-speed train, while entering a tunnel. This compression wave propa- gates to the tunnel exit and spouts out as a micro pressure wave, causing an exploding sound. In order to estimate the magnitude correctly, the mechanism of the attenuation and distortion of a compression wave propagating along a tunnel must be understood and experimental information on these phenomena is required. An experimental and numerical in- vestigation is carried out to clarify the mechanism of the propagating compression wave in a tube. The final objective of our study is to understand the mechanism of the attenuation and distortion of propagating compression waves in a tun- nel. In the present paper, experimental investigations are carried out on the transition of the unsteady boundary layer induced by a propagating compression wave in a model tunnel by means of a developed laser differential interferometry technique.

Source model of 2016 Mw6.6 Aketao earthquake,Xinjiang derived from Sentinel-1 InSAR observation

On 25 November 2016（14:24:30 UTC）, an Mw6.6 earthquake occurred in Aketao county of Xinjiang. We derived the coseismic deformation field of the earthquake from ESA’s Sentinel-1 B images and inverted the fault geometry and slip distribution by using a homogenous half-space elastic model and the Steepest Decent Method（SDM） program. The slip model shows that the rupture plane is about 68 km in length and 40 km in width and has an average strike of 105.2°SE and an average dip of 76.0°S. The average amount of slip is-0.16 m and the maximum amount of slip is 0.59 m. The estimated seismic moment is 1.31 × 1019 N·m and the corresponding moment magnitude is Mw6.68. The dislocation is mainly distributed in the depth of 5-22 km, where the rupture center is located at 39.170 E, 74.38°N, and a depth of-8.8 km, so this earthquake is a shallow earthquake. In terms of the tectonic settings, the earthquake was triggered by the release of residual stresses on the seismogenic Muji fault. The ruptures were stimulated simultaneously by the main shock, which made the slip distribution pattern of a strike-slip fault with a double fracture. Due to the tectonic setting and the seismic gap between the ruptures, the Muji fault would have a risk of rupture to some extent and trigger an earthquake in future.

Quantifying glacial elevation changes in the central Qilian Mountains during the early 21^(st) century

Glaciers in the central Qilian Mountains provide important water resources for the arid Hexi corridor and Qaidam Basin;however,changes in these glaciers interact with climate change.Twenty-four bi-static image pairs of TerraSAR-X add-on for Digital Elevation Measurement(TanDEM-X)data,in addition to a Shuttle Radar Topography Mission-C/X band digital elevation model,and the technology of iterative differential synthetic aperture radar interferometry were used to carry out glacier elevation change analysis in the central Qilian Mountains in China during 2000–2014.Glacier elevation changed with an average rate of(−0.47±0.06)m yr^(−1),while changes in elevation of(−0.51±0.06)m yr^(−1) and(−0.44±0.06)m yr^(−1) were found in the northern(including the Zoulangnan,Tuolai,and Tuolainan mountains)and southern(including the Shulenan and Hark mountains)regions,respectively.Summer mean temperature has risen by 0.51℃(10 yr)^(−1)in the northern region and 0.48℃(10 yr)^(−1) in the southern region during 1989–2014;however,the change in amplitude of annual precipitation was 2.69 mm yr^(−1) in the northern region and 4.77 mm yr^(−1) in the southern region for the same period.These changes can be ascribed as major driving factors for the differences in the changes in glacial elevation in the northern and southern regions.Four types of glaciers existed in the region when considering the change in elevation of the glacial tongue and variation in the position of the glacial terminus:surging,advancing,intensively retreating,and slightly retreating glaciers.If elevation decreased more than 20 m on the part of glacier tongue,the glacier terminus position had commonly retreated more than 100 m.

Variational denoising method for electronic speckle pattern interferometry

Traditional speckle fringe patterns by electronic speckle pattern interferometry （ESPI） are inherently noisy and of limited visibility, so denoising is the key problem in ESPI. We present the variational denoising method for ESPI. This method transforms the image denosing to minimizing an appropriate penalized energy function and solving a partial differential equation. We test the proposed method on computer- simulated and experimental speckle correlation fringes, respectively. The results show that this technique is capable of significantly improving the quality of fringe patterns. It works well as a pre-processing for the fringe patterns by ESPI.