InSAR Pairs Research Articles

Potential of EOS-4 imagery for SAR interferometry

ISRO recently launched the EOS-4 SAR satellite which is designed to provide images under all weather conditions for various applications. This paper reports on the generation of the Digital Elevation Model (DEM) from the EOS-4 interferometric pair of Alwar, Rajasthan, India. This is the first study on the feasibility of EOS-4 for SAR Interferometry (InSAR). The study finds that there exists proper coherency between the EOS-4 InSAR pair and the DEM has been generated through SAR interferometric processing algorithms which include Coregistration, Interferogram generation, Baseline estimation, Flattening of Interferogram, Phase unwrapping, Phase to height (DEM) conversion and Geocoding of DEM.

Pair Selection Optimization for InSAR Time Series Processing

AbstractThe ever‐increasing amount of Synthetic Aperture Radar (SAR) data motivates the development of automatic processing chains to fully exploit the opportunities offered by these large databases. The Synthetic Aperture Radar Interferometry (InSAR) Mass processing Toolbox for Multidimensional time series is an optimized tool to automatically download SAR data, select the interferometric pairs, perform the interferometric mass processing, compute the geocoded deformation maps, invert and display the velocity maps and the 2D time series on a web page updated incrementally as soon as a new image is available. New challenges relate to data management and processing load. We address them through methodological improvements dedicated to optimizing the InSAR pair selection. The proposed algorithm narrows the classical selection based on the shortest temporal and spatial baselines thanks to a coherence proxy and balances the use of each image as Primary and Secondary images thanks to graph theory methods. We apply the processing to three volcanic areas characterized with different climate, vegetation, and deformation characteristics: the Virunga Volcanic Province (DR Congo), the Reunion Island (France), and the Domuyo and Laguna del Maule area (Chile‐Argentina border). Compared to pair selection based solely on baseline criteria, this new tool produces similar velocity maps while reducing the total number of computed differential InSAR interferograms by up to 75%, which drastically reduces the computation time. The optimization also allows to reduce the influence of DEM errors and atmospheric phase screen, which increase the signal‐to‐noise ratio of the inverted displacement time series.

Investigation of temporal baseline effect on DEMs derived from COSMO Sky-Med data

Digital elevation models (DEM) are indispensable elements of sensitive earth science studies. It is important the production and usage of DEMs. The science of remote sensing offers scientists an important source of data on this subject. Radar data, which is an active remote sensing system, has an important capacity in this regard. DEM production using InSAR data has been widely used in the literature in the last decade. The temporal baseline parameter, which is an important factor in data generation from InSAR pairs, also affects the final products. In this study, it is aimed to examine the usability of these data by producing short (4days), medium (84 days) and long (440 days) baseline DEMs using InSAR pairs of COSMO Sky-Med satellite. At the same time, photogrammetric DEMs were produced with unmanned aerial vehicles (UAV) in selected pilot areas. The DEMs produced were evaluated in 4 land surface types, namely plain-bare, agricultural, urban and rugged area. In addition, by performing statistical analyzes such as RMSE, MAE, the accuracy of the produced DEMs compared to the DEMs produced with UAV was examined. The results showed that short and medium baseline data give more accurate results than long baseline InSAR pairs. Increasing the temporal baseline, increases the amount of error in the DEMs produced. Also, the effect of land surface types on the produced DEMs was revealed in the results of the study.

Optimization of three-dimensional multi-level surface deformation in mining areas through integration of deformation fusion model and Lagrange multiplier method based on single high resolution OTD-InSAR pair

Underground longwall mining activities usually induce three-dimensional (3-D) multi-level surface deformation, which could lead to serious natural hazards. Offset-tracking (OT) and differential interferometric synthetic aperture radar (DInSAR) technology (referred to as OTD-InSAR) can be used to observe the large-level and small-level mining deformations based on single InSAR pair, but the measured deformation is only along the radar line-of-sight (LOS) or the azimuth directions rather than in the 3-D directions. The conventional InSAR-based methods to resolve 3-D mining deformation have the strict restrictions and low south-north accuracy. In this paper, a novel methodology is proposed to utilize a multi-level deformation fusion model and the Lagrange multiplier method based on single OTD-InSAR pair (hereafter called MAOTD-InSAR) to estimate and optimize the 3-D multi-level surface deformation. The Daliuta coal mining area of China was selected to verify the feasibility and precision of the proposed method using high resolution TerraSAR-X (TSX) SAR images with six pairs. Results show that the root mean square errors (RMSEs) of MAOTD-InSAR against in-situ measured data are less than 0.2214 m, 0.1612 m and 0.1880 m in the east, north and vertical directions, respectively. The minimum RMSE in the horizontal direction could reach 0.0361 m with an improvement of about 82.6%, which particularly improve the accuracy in the south-north direction for the TSX satellite since its direction of azimuth deformation is approximately north direction, and this is also adequate for the other satellites in the near-polar orbit. In addition, an empirical model was generated with respect to the gradients of ground fissures on horizontal deformation, and this model enabled us to remove large errors caused by ground fissures. The verification results show that the proposed method provides higher precision and reliability for the resolved 3-D multi-level surface deformation, which presents 3-D mining deformation with more details from the edge to the center of the subsidence basin and will show some possibilities for new findings and interpretations in the process of coal mining.

SIP-Based Inversion Model of Mining-Induced 3D Deformation

Underground mining causes many forms of surface deformation, including vertical subsidence as well as strike and dip horizontal displacement. Differential interferometric synthetic-aperture radar (D-InSAR) has become a widely applied technique for precise and detailed mapping of the Earth's surface deformation caused by underground mining. However, the technology can only detect a one-dimensional displacement in the satellite's line of sight. To address this deficiency, we propose an improved three-dimensional displacement inversion model based on symmetry characteristics (imDIMSC) of a mining subsidence basin by the stacking technology of multiple single-track InSAR pairs. In this study, both field-observed surface displacement and simulated data were applied to calibrate and validate the proposed imDIMSC model. A methodology and algorithm were then developed to determine the symmetrical center for the two special mining circumstances. Comparison of the field-observed data, the proposed methodology, and the imDIMSC model provided significantly more accurate 3D displacement estimations.

Surface displacement revealed by L-band InSAR analysis in the Mayya area, Central Yakutia, underlain by continuous permafrost

Recent increases in global temperature have stimulated permafrost degradation associated with landform deformation caused by the melting of excess ground ice (thermokarst). Central Yakutia is underlain by ice-rich continuous permafrost, and there are complicated permafrost-related features in forested and deforested areas. This situation makes thermokarst monitoring necessary over a wide area to achieve a better understanding of its dynamics. As a case study, we applied L-band InSAR analysis to map surface subsidence due to thermokarst in this area and to demonstrate the suitability of L-band SAR for such monitoring. Our results show that InSAR detected subsidence/uplift signals in deforested areas and alasses; whereas, there were few ground deformation signals in forested areas with middle coherence. The InSAR stacking process, including both seasonal and inter-annual displacements, showed subsidence in deforested areas during 2007–2010 and 2015–2018, in the range of 0.5–3 cm yr−1. We also estimated the inter-annual subsidence to be up to 2 cm yr−1 during 2015–2018, using InSAR pairs that spanned the same seasonal interval but in different years. The magnitude of subsidence and the spatial patterns are qualitatively reasonable as thermokarst subsidence compared to observations using field surveys and high-resolution optical images. L-band InSAR was effective in maintaining coherence over a long period for a partially forested thermokarst-affected area, which resulted in deriving the inter-annual subsidence by the stacking using four interferograms. The advantage of the persistent coherence in L-band InSAR is crucial to better understand thermokarst processes in permafrost regions.

IMPROVED TOPOGRAPHIC MAPPING IN VEGETATED MOUNTAINOUS AREAS BY HIGH-RESOLUTION RADARGRAMMETRY-ASSISTED SAR INTERFEROMETRY

Abstract. In densely vegetated mountainous areas, the height measurement accuracy of SAR interferometry is contaminated by phase unwrapping errors and volume scattering effects of the vegetation. Aiming at this limitation of InSAR, we propose the high-resolution radargrammetry-assisted SAR interferometry method to achieve high-precision topographic mapping. Specifically speaking, we propose to apply our methods in the TerraSAR-X images with a repeat-pass InSAR pair and a stereo radargrammetric pair sharing the same master image which can avoid radarcoding the reference DEM and minimize the acquisition time discrepancy between the reference DEM and InSAR data. Compared with medium-resolution reference DEM, the high-resolution radargrammetric DEM can simulate the reference topographic phase more accurately which reduces the InSAR phase unwrapping errors. In addition to the removal of the reference topographic phase, we automatically select reliable points from radargrammetric DEM for calibrating the absolute InSAR phase offset. Finally, we fuse the radargrammetric DEM and InSAR DEM together with weights determined from theoretical height error to fill in data voids in InSAR DEM. The experimental results show that the DEM generated by radargrammetry-assisted SAR interferometry has better height accuracy than DEM generated by either single method.

Calculating vertical deformation using a single InSAR pair based on singular value decomposition in mining areas

Vertical deformation estimation can be a significant tool in preventing geological hazards and managing environment impacts of underground mining. Common ground surface vertical deformation calculations are challenged by difficult data collection and dependence on prior knowledge. SVD (singular value decomposition) method was applied to estimate ground surface vertical deformation from single pair SAR (synthetic aperture radar) data in a mining region. During the study, LOS (line of sight) and azimuth displacement was obtained using two pass D-InSAR (differential interferometry synthetic aperture radar) and MAI (multi-aperture radar interferometry) technology, respectively. Two adjustment equations were composed using the imaging geometry of D-InSAR and MAI. The singular value decomposition theorem was used to acquire M-P (Moore-Penrose) generalized inverse of the rank deficiency coefficient matrix. From this, the optimal approximation solution of unknown parameters was calculated using weighted least squares. A working panel in the Datong mining area, Shanxi province, China, was selected to verify the SVD approach using the two ascending Sentinel-1A data. The accuracy of vertical deformation estimated by SVD approach is reliable. The RMSE (root mean square error) of vertical deformation is 2.64 mm (along upright profile) and 4.95 mm (along horizontal profile). These results suggest that the SVD approach will complement widely used vertical ground surface deformation calculations. Further study is needed to validate the method from other deformation scenarios from landslides, groundwater loss, earthquakes, underground mining, and glacier movement.

Generation of high-quality digital elevation models by assimilation of remote sensing-based DEMs

Advanced spaceborne remote sensing techniques are currently available for the generation of high-resolution digital elevation models (DEMs) aiding in the advancement of Earth’s topographic modeling. DEM assimilation using data-driven models is a technique that can effectively overcome the limitations of individual DEMs generated from different techniques and sources of remote sensing data. The assimilation of DEMs generated from optical stereo pairs (Cartosat-1) and InSAR pair (ALOS PALSAR-1) was done for improving the DEM quality. Further, by using data assimilation techniques, the openly accessible DEM products derived from remote sensing datasets were used for generation of improved high-quality DEMs. The feature level fusion and the Kalman optimal interpolation techniques were used for the assimilation of these DEMs. Three sites, namely Dehradun, Jaipur, and Kendrapara, were selected on basis of topographic conditions, i.e., rugged, moderate, and gentle. RMSEs calculated for Dehradun and Jaipur have shown significant improvement in assimilated DEMs. Assimilation of CartoDEM V3 R1 and ALOS PALSAR RTC HR DEMs at the Jaipur site has resulted in highly improved RMSE in elevation of 1.22 m using the Kalman optimum interpolation model. However, in case of the plain region of Kendrapara, the CartoDEM V3 R1 data are found to have the highest accuracy of 2.00 m, indicating importance of selective use of input DEMs and assimilation methods.

The impacts of spatial baseline on forest canopy height model and digital terrain model retrieval using P-band PolInSAR data

Polarimetric Synthetic Aperture Radar Interferometry (PolInSAR) has shown potential for the retrieval of a forest canopy height model (CHM) and the underlying solid earth digital terrain model (DTM). However, because of non-volume decorrelation and other unavoidable errors, the robustness of retrieval heights is sensitive to the spatial baseline of the selected InSAR pairs, which relates forest parameters to measured coherence. Within the context of the random volume over ground (RVoG) model and the three-stage inversion method, we aimed to quantify the influence of spatial baseline on the inversions at P-band, which are distinct from the inversions at higher frequency due to the non-negligible ground contributions. This information assists in optimal baseline selection and the development of robust inversion schemes. Assumptions about the extinction coefficient and additional DTM or DEM were used to reduce the influence of ground contribution on CHM and DTM inversion, respectively. Inversions from published airborne repeat-pass P-band PolInSAR data with four different spatial baselines were validated against LiDAR-derived DTM and CHM data. The results show that a longer spatial baseline performed better in DTM inversion. The longest baseline produced the best R2 of 0.995 and RMSE of 0.555 m, much better than the smallest baseline with an R2 of 0.794 and RMSE of 3.74 m. A threshold height could be identified that determines the overestimation and underestimation of CHM inversion due to the non-volume decorrelation. Different baselines produced different threshold heights, making CHM inversion only accurate for a limited range of forest height around the threshold. The optimal baseline produced a CHM with R2 of 0.605 and RMSE of 2.67 m. Additionally, we found that using multiple baselines has the potential to improve CHM inversion, improving the R2 to 0.827 and RMSE to 0.876 m in our study.

A Study of Landfast Ice with Sentinel-1 Repeat-Pass Interferometry over the Baltic Sea

Mapping of fast ice displacement and investigating sea ice rheological behavior is a major open topic in coastal ice engineering and sea ice modeling. This study presents first results on Sentinel-1 repeat-pass space borne synthetic aperture radar interferometry (InSAR) in the Gulf of Bothnia over the fast ice areas. An InSAR pair acquired in February 2015 with a temporal baseline of 12 days has been studied here in detail. According to our results, the surface of landfast ice in the study area was stable enough to preserve coherence over the 12-day baseline, while previous InSAR studies over the fast ice used much shorter temporal baselines. The advantage of longer temporal baseline is in separating the fast ice from drift ice and detecting long term trends in deformation maps. The interferogram showed displacement of fast ice on the order of 40 cm in the study area. Parts of the displacements were attributed to forces caused by sea level tilt, currents, and thermal expansion, but the main factor of the displacement seemed to be due to compression of the drift ice driven by southwest winds with high speed. Further interferometric phase and the coherence measurements over the fast ice are needed in the future for understanding sea ice mechanism and establishing sustainability of the presented InSAR approach for monitoring dynamics of the landfast ice with Sentinel-1 data.

Flood Mapping Using InSAR Coherence Map

Abstract. Classic approaches for the detection of flooded areas are based on a static analysis of optical images and/or SAR data during and after the event. In this paper, we aim to extract the flooded zones by using the SAR image coupled with the InSAR coherence. A new formulation of the ratio approach for flood detection is given considering InSAR coherence. Our contribution is to take advantage from the coherence map provided using the InSAR pairs (one before and one after the event) to enhance the detection of flooded areas. We explore the fact that the coherence values during and after the flood are mainly differents on the flooded zones and we give a more suitable flood decision rule using this assumption. The proposed approach is tested and validated in the case of the flood taken place in 2005 in the region of Kef in Tunisia.

Correcting ionospheric effects and monitoring two-dimensional displacement fields with multiple-aperture InSAR technology with application to the Yushu earthquake

Differential synthetic aperture radar interferometry (D-InSAR) can only measure one-dimensional surface displacements along the line-of-sight (LOS) direction which greatly inhibits its development and application. In this paper, we introduce a novel approach to measuring two-dimensional (2-D) surface displacements by exploiting a single InSAR pair, which is called multi-aperture InSAR (MAI) technology. We study the effects of baseline errors and the ionosphere on MAI technology and develop a directional filter and interpolator to minimize the ionospheric effects. A PALSAR image pair covering the 2010 Yushu earthquake is used to estimate the 2-D displacement fields of the earthquake using the MAI approach. The experimental results show that MAI is superior to conventional Offset-Tracking and therefore has great potential in co-seismic displacement measurement and source parameter inversion.

Movement estimate of the Dongkemadi Glacier on the Qinghai–Tibetan Plateau using L-band and C-band spaceborne SAR data

We measured the complex motion of the Dongkemadi Glacier on Tanggula Mountain, Qinghai–Tibetan Plateau, using two-pass differential synthetic aperture radar interferometry (InSAR) with satellite L-band and C-band SAR data. We derived detailed motion patterns of the Dongkemadi Glacier for the winter seasons of 1996, 2007 and 2008 using a European Remote sensing Satellite-1/2 (ERS-1/2) tandem InSAR pair acquired from descending orbit and a 46-day-separation Advanced Land Observing Satellite (ALOS) InSAR pair acquired from ascending orbit. In this article, we focus on an analysis of the glacier's surface motion features and a validation of the results from the InSAR using Global Positioning System (GPS) survey data. The experimental results show that the glacier flow distribution displays strong spatial variations depending on elevation. The glacier is divided into four clearly defined fast-flowing units in terms of spatial variability of the glacier speed, with evidence from both ERS and ALOS/PALSAR InSAR pairs (palsar – Phased Array type L-band Synthetic Aperture Radar). Among the four fast-flowing units, three are on the Dadongkemadi Glacier (DDG) and one on the Xiaodongkemadi Glacier (XDG). The flow patterns are generally characterized by terrain complexity for both glacier branches. The upper central area of the DDG shows slow movement, maybe due to the convergent and uptaking effect of ice from steep slope areas with opposite flow directions.

Deformation mapping in three dimensions for underground mining using InSAR – Southern highland coalfield in New South Wales, Australia

This article presents 3D surface deformation mapping results derived from satellite synthetic aperture radar (SAR) data acquired over underground coal mines. Both ENVISAT Advanced Synthetic Aperture Radar (ASAR) and Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) data were used in this study. The quality of the 3D deformation mapping results due to underground mining is mainly limited by two factors. (1) Differential interferometric synthetic aperture radar (DInSAR) is less sensitive to displacement along the north–south direction in the case of the current SAR satellite configurations. (2) The mining-induced displacement is continuous and nonlinear; and the accuracy of the 3D DInSAR measurement is severely affected by the similar but non-identical temporal overlaps of the InSAR pairs. The simulation and real data analyzes have shown that it would be more practical to use DInSAR pairs with the assumption of negligible northing displacement to derive the displacements in the easting and vertical directions. The northing displacement could then be estimated from the residuals. This limitation could be overcome in the future with the launch of more radar satellites, which would provide better viewing geometry.

Using multiple RADARSAT InSAR pairs to estimate a full three-dimensional solution for glacial ice movement

[1] Multiple SAR interferograms are used to solve for the full 3-dimensional displacement of the surface of the Henrietta Nesmith Glacier in northern Ellesmere Island Canada. The approach exploits the incidence angle flexibility of different ascending and descending beam modes, and the azimuth angle diversity which occurs when different incidence angles are used at high latitudes. Line-of-sight displacements are estimated in 3 different orientations from the terrain corrected unwrapped differential phase and used to solve for the displacements in a local East, North, Up frame. Uncertainty in the absolute line-of-sight displacements limits the absolute accuracy for vertical displacement, however the relative solution coupled with knowledge of the surface slope allows spaceborne mapping of relative glacier thickening or thinning with unprecedented spatial resolution and with an accuracy of order a millimeter per day.

Error analysis in the digital elevation model of Kuwait desert derived from repeat pass synthetic aperture radar interferometry

The aim of this paper is to analyze the errors in the Digital Elevation Models (DEMs) derived through repeat pass SAR interferometry (InSAR). Out of 29 ASAR images available to us, 8 are selected for this study which has unique data set forming 7 InSAR pairs with single master image. The perpendicular component of baseline (B) varies between 200 to 400 m to generate good quality DEMs. The Temporal baseline (T) varies from 35 days to 525 days to see the effect of temporal decorrelation. It is expected that all the DEMs be similar to each other spatially with in the noise limits. However, they differ very much with one another. The 7 DEMs are compared with the DEM of SRTM for the estimation of errors. The spatial and temporal distribution of errors in the DEM is analyzed by considering several case studies. Spatial and temporal variability of precipitable water vapour is analysed. Precipitable water vapour (PWV) corrections to the DEMs are implemented and found to have no significant effect. The reasons are explained. Temporal decorrelation of phases and soil moisture variations seem to have influence on the accuracy of the derived DEM. It is suggested that installing a number of corner reflectors (CRs) and the use of Permanent Scatter approach may improve the accuracy of the results in desert test sites.

Measuring two‐dimensional movements using a single InSAR pair

We present a new method to extract along‐track displacements from InSAR data, based on split‐beam InSAR processing, to create forward‐ and backward‐looking interferograms. The phase difference between the two modified interferograms provides the along‐track displacement component. Thus, from each conventional InSAR pair we extract two components of the displacement vector: one along the line of sight, the other in the along‐track direction. We analyze the precision of the new method by comparing our solution to GPS and offset‐derived along‐track displacements in interferograms of the 1999, Hector Mine earthquake. The RMS error between GPS displacements and our results ranges from 5 to 8.8cm. Our method is consistent with along‐track displacements derived by pixel‐offsets, which are limited to 12–15cm precision. The theoretical precision of the new method depends on SNR and coherence. For a signal to noise ratio of 30 the expected precisions are 3, 11cm for coherence of 0.8, 0.4, respectively.

Detecting slope deformation using two‐pass differential interferometry: Implications for landslide studies on Earth and other planetary bodies

Landslide features have been identified on Earth and the Moon, Mars, Venus, as well on the Jovian moons. By focusing on a terrestrial landslide complex we test the operational parameters of RADARSAT‐1 and the use of two‐pass differential interferometry to detect change, to map its extent, and to measure the amount of movement over a given time period. RADARSAT‐1 was chosen because of its variable imaging modes and geometry. For investigations of landslide motions using remote sensing techniques, repeat‐pass data are required. Synthetic aperture radar (SAR) interferometry (InSAR) can ideally monitor movements across the whole surface of a landslide to a millimeteric precision, yielding a coverage significantly better than that obtained by ground instrumentation. Obtaining optimal data for InSAR analysis requires controlled orbital characteristics and imaging geometries, an understanding of the landslide characteristics and behavior, a cooperative surface, and mitigation of the factors that can affect phase. Using two‐pass differential interferometry, a slope deformation map has been generated from RADARSAT‐1 data for part of the Black Ven landslide (2°52′W, 50°40′N), on the south coast of England. Four months separate the InSAR pair during which time 0.03 m of subsidence was measured. From this a movement rate of 0.09 m/yr can be calculated. This agrees well with ground observations and an in situ record of movement, thus demonstrating that the technique can be used to investigate landslides. With further refinement it can provide more direct measurements of landslide deformation on Earth and other planetary bodies than are currently available.

The integration of JERS-1 and ERS SAR in differential interferometry for measurement of complex glacier motion

AbstractComplex glacier motion in the Grove Mountains region, Antarctica, is measured using four-pass differential synthetic aperture radar (SAR) interferometry (InSAR). The components of the motion vector field are resolved using a 44 day-separation Japanese Earth Resources Satellite-1 (JERS-1) InSAR pair and a European Remote-sensing Satellite-1/-2 (ERS-1/-2) tandem InSAR pair. The 44 day temporal baseline provides the sensitivity required to observe the range of ice motion (around 8–10ma–1), and the 1 day short baseline provides the best choice for glacier digital elevation model reconstruction. It is remarkable that the scattering field of the JERS-1 pair remained coherent over the long time interval and the interferometric fringes are clear. The overall ice flow is from east to west, downslope and towards Lambert Glacier. The regional flow is obstructed by nunataks extending north–south, with two wide gaps. Two narrow glaciers flow past the nunataks and rejoin each other at the downstream end. Regional morphology, and the resolved flow in the Grove Mountains area, suggests that ice flow is channeled throughout this eastern flank of Lambert Glacier.