InSAR System Research Articles

GB‐InSAR interferogram processing method to generate DEM based on PS technology

Ground-based interferometry synthetic aperture radar (GB-InSAR) technology is becoming an important terrain mapping technology as it has the characteristics of short observation intervals, flexible operation environment and high data precision. Compared with air/space borne InSAR system, it is much easier for GB-InSAR to acquire repeat-pass/short-baseline data set, which can bring huge convenience on permanent scatterer (PS) technology. By using PS technology, on the one hand, the error caused by low coherence can be avoided, and on the other hand, the speed of the phase unwrapping part can be increased. In order to overcome the disadvantages of the non-uniform PS points distribution and low coherence cavities, the Kriging interpolation method is used to get an uniform digital elevation model (DEM) eventually. This study proposed a GB-InSAR interferogram processing method. First, it proposes a PS point selection method considering both accuracy and efficiency. Second, the study shows a network programming phase unwrapping method to unwrap the PS points. Then, Kriging interpolation method is analysed and used to fill the low coherence cavities. Finally, a field test is carried out in an open pit in Hebei, China. The DEM result of the observation area is shown to verify the correctness of this study's method.

Analysis and correction of spatial variant background ionosphere impacts on single‐pass InSAR system

Compared with the repeat-pass interferometry synthetic aperture radar (InSAR) system, the single-pass InSAR system, such as TanDEM-X and TanDEM-L, has better performance and less decorrelation. However, InSAR measurements can be seriously influenced by the background ionosphere, especially for InSAR system operating at lower frequencies, such as L-band and P-band. Low-frequency signals propagating in the ionosphere suffer serious group delay, dispersion, scintillation and Faraday rotation, which further induce the image shift and decorrelation of SAR interferometry pairs. Since the ionosphere shows significant space-varying and time-varying features, the conventional ionosphere spatial invariant model is invalid for space-borne single-pass InSAR system. It is supposed that the time variance of ionosphere in short integration time can be neglected for low-earth orbit InSAR system. The effect of the spatial variant ionosphere on single-pass InSAR measurement is analysed and a correction method for InSAR products based on the prior knowledge is presented in this paper. Simulations are performed by using total electron content data obtained from the international reference ionosphere model, and the results indicate the significant error induced by spatial variant ionosphere.

Optimal Baseline Design for Multibaseline InSAR Phase Unwrapping

Multibaseline (MB) synthetic aperture radar interferometry (InSAR) has the potential to improve the traditional single-baseline InSAR from the ill-posed problem to the well-posed problem. It is because MB InSAR phase unwrapping (PU) can take advantage of the baseline diversity to significantly increase the ambiguity intervals of interferometric phases, so it completely overcomes the limitation of the phase continuity assumption. However, due to the mathematical foundation of most of the MB PU methods, i.e., the Chinese remainder theorem (CRT), has poor measurement bias robustness (measurement bias could be caused by surface deformation, atmospheric artifact, and phase noise), CRT is sensitive to the normal baseline length. In other words, even if we choose the same CRT-based MB PU method, different system baseline lengths could result in different PU performances. Therefore, how to choose the baseline lengths to optimize CRT performance is crucial to all the CRT-based MB PU methods. In this paper, a nonlinear mixed-integer programming-based baseline design criterion (referred to NIP criterion) is proposed to maximize the measurement bias tolerance of the CRT-based MB PU. The optimality condition of the NIP criterion quantitatively provides important instructions for the CRT-based MB PU applications and offers significant guidance in the development of the practical MB InSAR system. The experiment results are shown to verify the effectiveness of the NIP criterion by using three representative CRT-based MB PU methods.

Height estimation improvement via motion compensation based on sub‐aperture method for interferometry SAR system

Baseline is the key factor for highly accuracy terrain elevation measurement in InSAR system. Variation of baseline attitude induced by aircraft's unstable motion leads to phase errors varying along the aperture. The variation will generate prodigious deterioration in DEM's precision. Therefore, in order to reduce the phase errors, critical motion compensation has to be implemented. Here, the sub-aperture method is introduced to resolve the above issue. The new method is described with mathematical analysis and modelling. The influence of the new method on the sensitivity of roll estimation is also analysed. The simulation and real testing show a very positive result. The roll errors are eliminated greatly in case the sub-aperture length is optimised. Moreover, the requirements of SNR and azimuth resolution are satisfied.

Going to Any Lengths: Solving for Fault Size and Fractal Slip for the 2016, Mw 6.2 Central Tottori Earthquake, Japan, Using a Transdimensional Inversion Scheme

AbstractMany earthquake properties, including slip, show self‐similar (fractal) features. We can incorporate self‐similarity into Bayesian slip inversions via von Karman correlation, so that the regularization applied is representative of observed fault features. In von Karman regularization, each slip patch has a relationship to every other patch. This means that von Karman regularization only has meaning when applied to patches that actually slipped; if applied to nonslipping patches, spurious slip can be added to meet the von Karman correlation criteria. Additionally, the fault size, usually chosen in advance, also affects the von Karman correlation lengths meaning that the final slip solution may be biased by initial geometry choices. Here we present a method for solving for the size of the fault plane during the slip inversion process, as well as slip, rake, and a hyperparameter controlling slip variance. We use a transdimensional Bayesian inversion scheme constrained by geodetic surface displacements and regularized using von Karman correlation. We use circular harmonics to solve for the size of the slipping area, to allow for a complex shape that is connected and continuous across the fault. We apply this method to the 2016 Mw 6.2 Central Tottori earthquake, Japan, constrained by interferometric synthetic aperture radar InSAR (Sentinel‐1 and ALOS‐2) and Global Navigation Satellite System data (GNSS). We find an area of slip extending from approximately 2‐ to 10‐km depth, with the slipping area elongated in the downdip direction. In contrast to some seismic studies, we find slip ruptured most of the seismogenic layer.

Generation of Large-Scale Moderate-Resolution Forest Height Mosaic With Spaceborne Repeat-Pass SAR Interferometry and Lidar

This paper provides an overview of the scattering model, inversion approach, and validation of the application results for creating large-scale moderate-resolution (hectare-level) mosaics of forest height through using spaceborne repeat-pass SAR interferometry and lidar. By incorporating several improvements to the forest height inversion and mosaicking approach, the height estimation accuracy along with the robustness of this approach have been considerably enhanced from its originally reported accuracy of RMSE of 3–4 m at a 20-hectare aggregated pixel size to RMSE of 3–4 m on the order of 3–6 hectares. Furthermore, practical data processing schemes are provided in detail. Extensive validation results are demonstrated which include: 1) a forest height mosaic (total area of 11.6 million hectares) is generated for the U.S. states of Maine and New Hampshire using Japanese Aerospace Exploration Agency’s (JAXA) ALOS-1 InSAR correlation data and a small airborne lidar strip (44 000 hectares); 2) the mosaic height estimates are further compared with the available airborne lidar data and field measurements over both flat and mountainous areas; and 3) feasibility of using modern repeat-pass InSAR satellites with short repeat interval is also examined by using JAXA’s ALOS-2 data. This simple and efficient approach is a potential observational prototype with much smaller error budget for the future spaceborne repeat-pass L-band InSAR systems with small spatial baseline and moderate/large temporal baseline (such as NISAR) in combination with lidar (such as GEDI) on the application of large-scale forest height/biomass mapping. It also serves as a complementary tool to the spaceborne single-pass InSAR systems using InSAR/PolInSAR methods when full-pol data are not available and/or when the underlying topography slope causes problems for these approaches.

Antenna Phase Center Calibration for Array InSAR System Based on Orthogonal Subspace

The array InSAR system obtains a three-dimensional image of an observed scene using a combination of pulse compression and synthetic and real aperture techniques. However, Antenna Phase Center (APC) errors can occur within a practical array InSAR system, which thus degrades the imaging quality in a height direction. The aim of this paper is to improve calibration problems occurring with APC errors. The effect of APC errors is analyzed, and a calibration method based on the orthogonal subspace principle is proposed that utilizes SAR Single Look Complex (SLC) to obtain the noise subspace through eigenvalue decomposition. The subspace orthogonal principle is then used to solve the APC positions of multiple channels simultaneously. In addition, a calibration scheme for the APC position is presented for application with an array InSAR system. The effectiveness of the proposed calibration method is verified using simulations and experimental results.

Feasibility of the Sentinel-1 Multi-temporal InSAR system based on the SNAP and StaMPS: Case study from the Tatra Mts., Slovakia

We present first full-resolution and large area Sentinel-1 multi-temporal InSAR analysis of the Tatra Mts. region within Slovakia as a case study on a feasibility of processing chain based on the Sentinels Application Platform (SNAP) and Stanford method for Persistent Scatterers (StaMPS). We utilize all Sentinel-1 data from three individual orbits, acquired from the beginning of the mission until the end of 2017. Study area was chosen to test the performance of our system over mountainous and sparsely urbanized land characteristic for strong atmospheric perturbations. Our results reveal several distinct areas of small-scale deformation phenomena, e.g. rockslides or land subsidence. InSAR displacement time series are validated via GNSS observations at the points of Slovakian permanent reference network. We conclude with the potential of proposed workflow for the future Slovakian nation-wide multi-temporal InSAR processing.

Determination of The Water Catchment Area in Semarang City Using a Combination of Object Based Image Analysis (OBIA) Classification, InSAR and Geographic Information System (GIS) Methods Based On a High-Resolution SPOT 6 Image and Radar Imagery

Semarang is the biggest city in central Java-Indonesia which has a rapid and massive infrastructure development nowadays. In order to control water resources and flood, the local goverment has been built east and west flood canal in Kaligarang and West Semarang River. One of main problem in Semarang city is the lack of fresh water in dry season because ground water is not rechargeable well. Rechargeable groundwater ability depends on underground water recharge rate and catchment area condition. The objective of the study is to determine condition and classification of water catchment area in Semarang city. The catchment area conditions will be determine by five parameters as follows soil type, land use, slope, ground water potential and rainfall intensity. In this study, we use three methods approach to solve the problem which is segmentation classification to acquire land use classification from high resolution imagery using nearest neighborhood algorithm, Interferometric Synthetic Aperture Radar (SAR) to derive DTM from SAR Imagery and multi criteria weighting and spatial analysis using GIS method. There are three types optical image (ALOS PRISM, SPOT-6 and ALOS PALSAR) to calculate water catchment area condition in Semarang city. For final result, this research will divide the water catchment into six criteria as follows good, naturally normal, early critical, a little bit critical, critical and very critical condition. The result shows that water catchment area condition is in an early critical condition around 2607,523 Ha (33,17 %), naturally normal condition around 1507,674 Ha (19,18 %), a little bit critical condition around 1452,931 Ha (18,48 %), good with 1157,04 Ha (14,72 %), critical with 1058,639 Ha (13,47 %) and very critical with 75,0387 Ha (0,95 %). The distribution of water catchment area conditions in West and East Flood Canal have an irreguler pattern. In northern area of watershed consists of begin to critical, naturally normal and good condition. Meanwhile in southern area of watershed consists of a little bit critical, critical and very critical condition.

Landslide monitoring by fixed-base terrestrial stereo-photogrammetry

Abstract. Photogrammetry has been used since long to periodically control the evolution of landslides; however, true monitoring is reserved to robotic total stations and ground based InSAR systems, capable of high frequency, high accurate 24h/day response. This paper presents the first results of a fixed terrestrial stereo photogrammetric system developed to monitor shape changes of the scene. The system is made of two reflex cameras, each contained in a sealed box with a control computer that periodically acquires an image and send it to a host computer; once an image pair is received from the two cameras, the DSM of the scene is generated by image correlation and made available for archiving or analysis. The system has been installed and is being tested on the Mont de la Saxe landslide, where several monitoring system are active. Some instability of the camera attitude has been noticed and is corrected with an automated procedure. First comparisons with InSAR data show a good agreement.

Research on Block Adjustment of Airborne InSAR Images

Airborne InSAR system and InSAR data processing algorithm have been one of the hot topics in the international SAR field. Geometric constraint relation of images is set up through airborne InSAR block adjustment, adjustment parameters are adjusted and refined, and the three-dimensional(3D) ground coordinates of tie-points(TPs) are solved according to least squares theory. The number of the ground control points(GCPs) is reduced. The airborne InSAR block adjustment experiment was done using self-developed Airborne InSAR Block Adjustment Software System. The 76 airborne InSAR images which are 0.5 m resolution and cover an area of 472 square kilometers generated a block of 4 strips and 19 rows with approximately 30% overlap between adjacent strips. The study site is located in in Jiangyou Sichuan province and characterized by a hilly topography. The result meets DEM and DOM mapping accuracy requirements at scale of 1:10000.

MELISSA, a new class of ground based InSAR system. An example of application in support to the Costa Concordia emergency

Ground Based Interferometric Synthetic Aperture Radars (GB-InSAR) have proved to be fully operational tools for the monitoring of ground displacement and structural deformation. The main limiting factor of the existing systems is the time to acquire a single image, typically ranging from few seconds to few minutes. This paper presents the validation and the operational use of a new system – Mimo Enhanced LInear Short SAr (MELISSA), belonging to a new class of GB-InSAR devices. MELISSA is based on a Multiple Input Multiple Output Synthetic Aperture Radar (MIMO SAR) and is capable of acquiring and processing image data at an unprecedented high speed. A configuration of the system acquiring a 0.96m synthetic aperture and 260m swath image in 2.6ms was tested in a controlled environment. The results prove its ability to reach an image refreshing time smaller than 4ms and Line-Of-Sight (LOS) displacement accuracies better than 10μm. Thus, MELISSA was able to help with the monitoring of the Costa Concordia ship movements in the immediate aftermath of grounding during both the rescue operations and subsequent wreckage removal. The accurate displacement measurements of specific points of the structure are presented in a global interferogram sequence (2-D displacement maps of the whole structure). The collected data contributed to a precise wreck deformation reconstruction. MELISSA’s ability to update the information almost every second has proven to be extremely reassuring as early warning on potentially catastrophic movements.

Research Development of High Precision Real-time Airborne InSAR System

The technique of Interferometric Synthetic Aperture Radar can generate high precise Digital Elevation Model (DEM) fast, which makes it play a very important role in the development of social economy and construct of national defense. Once the high precise DEM can be acquired in real-time, the worthiness of the technique will be embodied fully. In this thesis, the research dynamic of generating DEM in real-time at home and abroad is discussed in detail, the characteristic of the several interferometric system at home and abroad acquired some progress in course of real-time interferometry processing is introduced, the key techniques in acquiring DEM in real-time are summarized and analyzed, and finally the development trend is discussed.

Design of Multi-Mode Microwave Control Combination for InSAR System

This paper provides a multi-mode Microwave Control Combination (MCC) for InSAR system, where the center frequency is F0 with 800 MHz bandwidth, and the size is smaller than 355mm×480mm×155mm. A special InSAR system is introduced with finite baseline between antennas, gets the equal baseline longer by the way of MCC fast switch and makes the channel phrase satisfy the special InSAR system demand. In the MCC design, isolation between antenna channels, high-power and fast channel switch of the system are considered firstly, which are very important in finite airborne space for this InSAR system. The combination system can be changed to three working modes with different configuration but same external interface. This MCC can support average power 400w and peak power 4000w, achieve isolation between radiation channels more than 48dB and channel switch time less than 10μs.

A Systematical Study on the Accuracy of Air-Borne InSAR System in DGPS/IMU

With respect to the principle of Digital Elevation Modeling (DEM), through analyzing on the overall measurement accuracy of an InSAR in DGPS/IMU, the authors have mathematically inferred that the dominant factors for system accuracy are: Baseline Length, Baseline Inclination Angle, Radar Side-looking Angle, Phase Difference, the distance from radar antenna to various ground target points, Positioning Coordinate and Velocity of the flying platform, Center Doppler Estimation and such on, put forth a set of delicate formula for the factors on system measurement accuracy and error, verified the aforementioned outcomes by a variety of digital simulations, and thus established the principle in system design for air-borne InSAR system. Therefore, this paper is consequential for surveying and mapping both in theory and engineering.

SOURCES OF ARTEFACTS IN SYNTHETIC APERTURE RADAR INTERFEROMETRY DATA SETS

Abstract. In recent years, much attention has been devoted to digital elevation models (DEMs) produced using Synthetic Aperture Radar Interferometry (InSAR). This has been triggered by the relative novelty of the InSAR method and its world-famous product—the Shuttle Radar Topography Mission (SRTM) DEM. However, much less attention, if at all, has been paid to sources of artefacts in SRTM. In this work, we focus not on the missing pixels (null pixels) due to shadows or the layover effect, but rather on outliers that were undetected by the SRTM validation process. The aim of this study is to identify some of the causes of the elevation outliers in SRTM. Such knowledge may be helpful to mitigate similar problems in future InSAR DEMs, notably the ones currently being developed from data acquired by the TanDEM-X mission. We analysed many cross-sections derived from SRTM. These cross-sections were extracted over the elevation test areas, which are available from the Global Elevation Data Testing Facility (GEDTF) whose database contains about 8,500 runways with known vertical profiles. Whenever a significant discrepancy between the known runway profile and the SRTM cross-section was detected, a visual interpretation of the high-resolution satellite image was carried out to identify the objects causing the irregularities. A distance and a bearing from the outlier to the object were recorded. Moreover, we considered the SRTM look direction parameter. A comprehensive analysis of the acquired data allows us to establish that large metallic structures, such as hangars or car parking lots, are causing the outliers. Water areas or plain wet terrains may also cause an InSAR outlier. The look direction and the depression angle of the InSAR system in relation to the suspected objects influence the magnitude of the outliers. We hope that these findings will be helpful in designing the error detection routines of future InSAR or, in fact, any microwave aerial- or space-based survey. The presence of outliers in SRTM was first reported in Becek, K. (2008). Investigating error structure of shuttle radar topography mission elevation data product, Geophys. Res. Lett., 35, L15403.

REQUEST ANALYSIS OF DGPS/IMU ON THE AIR-BORNE INSAR SYSTEM

Abstract. The DGPS/IMU can measure position and velocity extremely high, and it is widely used in air-borne InSAR system. The passage based on the DGPS/IMU's action in the airborne InSAR system, makes sure the interference phase accuracy, from the analysis of the interference phase accuracy influence by InSAR imaging motivation compensation makes sure the interference phase accuracy, and analyzes the system's request of DGPS/IMU from the DEM accuracy's influence by DGPS/IMU's surveying error. At last the paper advances the accuracy request of the DGPS/IMU system, and provides basis for the InSAR system's selection of DGPS/IMU system.

Ground Moving Target Indication and Velocity Estimation Using an InSAR System

For InSAR systems with both along track baseline and cross track baseline, referred to as the hybrid baseline for simplicity, can be used to perform GMTI and DEM generation simultaneously. However, the cross-track baseline of such system is sensitive to the terrain fluctuation which badly affects the performance of clutter suppression. To solve the problem above, a GMTI method which takes advantage of the coherence information of neighboring pixel pairs of SAR images is presented in this paper. After neighboring pixel pairs are jointly used to compensate the terrain interferometric phase, an adaptive filtering method is used to suppress the stationary clutter with the benefit of calibrating the sensor responses. In addition, the accuracy of velocity estimation is improved due to the improvement of clutter suppression. Stimulation experiments illustrate the effectiveness of the proposed algorithm.

Analysis of the Effect of Radio Frequency Interference on Repeat Track Airborne InSAR System

工作在低频段的SAR 容易受到射频干扰(Radio Frequency Interference, RFI)的影响，而导致SAR图像质量的恶化。对于重复轨道InSAR来说，RFI的存在还会影响其干涉相位。针对此问题，该文将实测RFI信号加入仿真的典型圆锥场景回波，进行成像和干涉处理，给出了干扰前后的成像和干涉处理结果，分析了实测RFI对SAR 图像幅度、相位和重复轨道干涉处理的影响。最后使用频域陷波方法对机载P波段重复轨道InSAR实际数据中的RFI信号进行干扰抑制，给出了干扰抑制前后的重复轨道干涉处理结果，验证了仿真分析的正确性，表明了该文干扰抑制方法对减小由RFI引入干涉相位误差的有效性。

An Approach Based on Sinusoidal Model for RFI Suppression in InSAR System

The spectrum of P-band is heavily used for commercial communication,radio broadcast and so on.So there will be Radio Frequency Interference(RFI) in received signals.To resolve the problem of RFI suppression,an approach which can preserve phase information is presented.It is based on sinusoidal parametric model and adopts threshold detection and iterative strategy.The approach can both suppress RFI and preserve phase information which is especially important for InSAR system.Results using simulation data shows high-performance of the algorithm.