When multiple ground-based radars (GB-rads) are utilized together to resolve three-dimensional (3-D) deformations, the resolving accuracy is related with the measurement geometry constructed by these radars. This paper focuses on constrained geometry analysis to resolve 3-D deformations from three GB-rads. The geometric dilution of precision (GDOP) is utilized to evaluate 3-D deformation accuracy of a single target, and its theoretical equation is derived by building a simplified 3-D coordinate system. Then for a 3-D scene, its optimal accuracy problem is converted into determining the minimum value of an objective function with a boundary constraint. The genetic algorithm is utilized to solve this constrained optimization problem. Numerical simulations are made to validate the correctness of the theoretical analysis results.
Affected by the natural environmental and human activity factors, significant seasonal differences appear on the regional scattering characteristic and ground deformation of saline soil. Interferometric decorrelation due to season replacement limits the conventional multi-temporal interferometric synthetic aperture radar (MT-InSAR) technique and its application in such areas. To extend the monitoring capability in the salt desert area, we select a vast basin of saline soil around Howz-e-Soltan Salt Lake of Iran as the study area and present an improved MT-InSAR for experimental research. Based on 131 C-band Sentinel-1A images collected between October 2014 to July 2020,1896 refined interferograms in total are selected from all interferogram candidates. Interferometric coherence analysis shows that the coherence in the saline soil area has an apparent seasonal variation, and the soil moisture affected by the precipitation may be the main factor that leads to the seasonal variation. Subsequently, the deformation characteristics of saline soil under different environmental conditions and human activity factors are compared and analyzed in detail. Related deformation mechanisms of different saline soil types are initially revealed by combining interferometric coherence, meteorological data, and engineering geological characteristics of saline soil. Related results would provide reference for the large-scale infrastructure construction engineering in similar saline soil areas.
The permafrost development in the Qinghai-Tibet Engineering Corridor (QTEC) is affected by natural environment changes and human engineering activities. Human engineering activities may damage the permafrost growing environment, which in turn impact these engineering activities. Thus high spatial-temporal resolution monitoring over the QTEC in the permafrost region is very necessary. This paper presents a method for monitoring the frozen soil area using the intermittent coherence-based small baseline subset (ICSBAS). The method can improve the point density of the results and enhance the interpretability of deformation results by identifying the discontinuous coherent points according to the coherent value of time series. Using the periodic function that models the seasonal variation of permafrost, we separate the long wavelength atmospheric delay and establish an estimation model for the frozen soil deformation. Doing this can raise the monitoring accuracy and improve the understanding of the surface deformation of the frozen soil. In this study, we process 21 PALSAR data acquired by the Alos satellite with the proposed ICSBAS technique. The results show that the frozen soil far from the QTR in the study area experiences frost heave and thaw settlement (4.7 cm to 8.4 cm) alternatively, while the maximum settlement along the QTR reaches 12 cm. The interferomatric syntnetic aperture radar (InSAR)-derived results are validated using the ground leveling data nearby the Beiluhe basin. The validation results show the InSAR results have good consistency with the leveling data in displacement rates as well as time series. We also find that the deformation in the permafrost area is correlated with temperature, human activities and topography. Based on the interfering degree of human engineering activities on the permafrost environment, we divide the QTEC along the Qinghai-Tibet Railway into engineering damage zone, transition zone and natural permafrost.
Synthetic aperture radar (SAR) is able to detect surface changes in urban areas with a short revisit time, showing its capability in disaster assessment and urbanization monitoring. Most presented change detection methods are conducted using couples of SAR amplitude images. However, a prior date of surface change is required to select a feasible image pair. We propose an automatic spatio-temporal change detection method by identifying the temporary coherent scatterers. Based on amplitude time series, ${\chi ^2} $ -test and iterative single pixel change detection are proposed to identify all step-times: the moments of the surface change. Then the parameters, e.g., deformation velocity and relative height, are estimated and corresponding coherent periods are identified by using interferometric phase time series. With identified temporary coherent scatterers, different types of temporal surface changes can be classified using the location of the coherent periods and spatial significant changes are identified combining point density and F values. The main advantage of our method is automatically detecting spatio-temporal surface changes without prior information. Experimental results by the proposed method show that both appearing and disappearing buildings with their step-times are successfully identified and results by ascending and descending SAR images show a good agreement.
In the application of persistent scatterer interferometry (PSI), deformation information is extracted from persistent scatterer (PS) points. Thus, the density and position of PS points are critical for PSI. To increase the PS density, a time-series InSAR chain termed as “super-resolution persistent scatterer interferometry” (SR-PSI) is proposed. In this study, we investigate certain important properties of SR-PSI. First, we review the main workflow and dataflow of SR-PSI. It is shown that in the implementation of the Capon algorithm, the diagonal loading (DL) approach should be only used when the condition number of the covariance matrix is sufficiently high to reduce the discontinuities between the joint images. We then discuss the density and positioning accuracy of PS when compared with traditional PSI. The theory and experimental results indicate that SR-PSI can increase the PS density in urban areas. However, it is ineffective for the rural areas, which should be an important consideration for the engineering application of SR-PSI. Furthermore, we validate that the positioning accuracy of PS can be improved by SR-PSI via simulations.
For ship targets with complex motion, it is difficult for the traditional monostatic inverse synthetic aperture radar (ISAR) imaging to improve the cross-range resolution by increasing of accumulation time. In this paper, a distributed ISAR imaging algorithm is proposed to improve the cross-range resolution for the ship target. Multiple stations are used to observe the target in a short time, thereby the effect of incoherence caused by the complex motion of the ship can be reduced. The signal model of ship target with three-dimensional (3-D) rotation is constructed firstly. Then detailed analysis about the improvement of cross-range resolution is presented. Afterward, we propose the methods of parameters estimation to solve the problem of the overlap or gap, which will cause a loss of resolution and is necessary for subsequent processing. Besides, the compressed sensing (CS) method is applied to reconstruct the echoes with gaps. Finally, numerical simulations are presented to verify the effectiveness and the robustness of the proposed algorithm.
