Interferometric Synthetic Aperture RADAR and Radargrammetry towards the Categorization of Building Changes

The purpose of this work is the investigation of SAR techniques relying on multi image acquisition for fully automatic and rapid change detection analysis at building level. In particular, the benefits and limitations of a complementary use of two specific SAR techniques, InSAR and radargrammetry, in an emergency context are examined in term of quickness, globality and accuracy. The analysis is performed using spaceborne SAR data

Extraction of spatial information from sterioscopic SAR images

Synthetic Aperture Radar (SAR) is now widely used for generating Digital Elevation Models (DEMs) and has advantages over optical data in terms of availability as it allows all-day and all-weather operations. The stereoscopic SAR method, which allows direct extraction of spatial information in three-dimensional space, has been established for decades. However, the traditional stereoscopic methods developed for SAR data depend on many human operations and need ground control points (GCPs), to set up geometric models. The aims of the thesis are not only to propose a refined rigorous stereoscopic SAR method and a new error model to predict theoretic errors, but also to achieve a higher level of automation and accuracy. By using a weighting matrix, which is derived by considering different observations in the space intersection algorithm, the minimal number of the GCPs required for the refined algorithm is only two. To achieve a high degree of automation, an optimized strategy of parameter selection for the pyramidal image correlation scheme employing a region-growing technique has been proposed. This avoids a trial-and-error approach to produce digital parallax data from the same-side SAR image pairs. A new method to derive GCPs automatically has been developed using a SAR image simulation technique, under the condition that a known DEM chip is available, to minimize human interventions and operator error. The proposed method for providing GCPs and the DEMs generated from space intersection have been incorporated into the procedures for geocoding SAR images to validate the proposed algorithms. The results derived show that the stereoscopic SAR data can be applied to geometric rectification in flat-to-moderate areas, and other applications of extraction of spatial information are promising

Digital elevation modelling by radargrammetry in real-beam ground mapping mode

In this thesis the problem of estimating terrain elevation using two-dimensional radar data from the multirole ghter aircraft JAS 39 Gripen is considered. Radar data contains information about range from the aircraft to the reflecting terrain, as well as horizontal angle. In general, radar data has high resolution in range and low resolution in angle, giving rise to interesting problems. A new radar with higher resolution is in development for the next-generation Gripen. This thesis aims at answering whether estimation of terrain height can be done using available radar data, in order to evaluate the plausibility of doing this with data from the new radar. The approach is to find matching terrain features in subsequent images of the ground, and use this information to calculate terrain elevation. Two approaches are implemented and studied, both on simulated radar data and on real datasets. One approach uses Harris corner detection and the other uses Speeded-Up Robust Features (SURF). Conclusions drawn are that the algorithms do not work for the available radar data, but that they possibly could work when higher resolution data from the new radar is available

Optimal Parameters for DEM Extraction from IKONOS Data: A Case Study of a Coastal Area

The gap between aerial and satellite photogrammetry is getting smaller as both systems have benefited from great technology improvements in the last years. However, the major advantage of earth observation satellites continues to be the possibility to acquire data virtually anywhere on the planet without considering border and logistical restrictions and over huge extensions. A pair of stereo images corresponding to a coastal area in the NW of Spain is the basis for this paper, which analyzes certain influential variables in the process of generating a Digital Elevation Model (DEM) from stereoscopic pairs of IKONOS images. The mathematical model, the number of Ground Control Points (GCPs) and their accuracies are analyzed through a sequence of experimental trials. Two main methods are applied for math modeling: a CCRS model (rigorous model) and a Rational Functions model. The influence of the GCPs’ positional quality is compared using two different information sources: points measured in 1:5,000 cartography and points surveyed via GPS. The number of GCPs tested varies between 0 and 20. Using different configurations of these variables, 17 models are generated. The best results are achieved with the rigorous model and 16 GCPs measured with GPS with an RMSE of 1.01 m (or an LE95 –Linear Error in Z at 95% confidence level- of 2 m), which is approximately the pixel size of the initial pair. The mathematical model was determined to be the variable with the most influence on accuracy. Moreover, the results suggest that the use of 10-16 GCPs is sufficient. Additional points do not improve the DEM accuracy or may even worsen it in certain cases. Although the study is carried out in a coastal zone, which restricts the GCPs’ distribution possibilities, the results are comparable with similar results from inland areas.This study has been carried out in the framework of the “Financial aid for the consolidation and structure of competitive units of investigation in the universities of the University Galician System (2016-18)” Ref. ED431B 2016/030. This work has been also supported in the same program by Ref. ED341D R2016/023S

Elevation and Deformation Extraction from TomoSAR

3D SAR tomography (TomoSAR) and 4D SAR differential tomography (Diff-TomoSAR) exploit multi-baseline SAR data stacks to provide an essential innovation of SAR Interferometry for many applications, sensing complex scenes with multiple scatterers mapped into the same SAR pixel cell. However, these are still influenced by DEM uncertainty, temporal decorrelation, orbital, tropospheric and ionospheric phase distortion and height blurring. In this thesis, these techniques are explored. As part of this exploration, the systematic procedures for DEM generation, DEM quality assessment, DEM quality improvement and DEM applications are first studied. Besides, this thesis focuses on the whole cycle of systematic methods for 3D & 4D TomoSAR imaging for height and deformation retrieval, from the problem formation phase, through the development of methods to testing on real SAR data. After DEM generation introduction from spaceborne bistatic InSAR (TanDEM-X) and airborne photogrammetry (Bluesky), a new DEM co-registration method with line feature validation (river network line, ridgeline, valley line, crater boundary feature and so on) is developed and demonstrated to assist the study of a wide area DEM data quality. This DEM co-registration method aligns two DEMs irrespective of the linear distortion model, which improves the quality of DEM vertical comparison accuracy significantly and is suitable and helpful for DEM quality assessment. A systematic TomoSAR algorithm and method have been established, tested, analysed and demonstrated for various applications (urban buildings, bridges, dams) to achieve better 3D & 4D tomographic SAR imaging results. These include applying Cosmo-Skymed X band single-polarisation data over the Zipingpu dam, Dujiangyan, Sichuan, China, to map topography; and using ALOS L band data in the San Francisco Bay region to map urban building and bridge. A new ionospheric correction method based on the tile method employing IGS TEC data, a split-spectrum and an ionospheric model via least squares are developed to correct ionospheric distortion to improve the accuracy of 3D & 4D tomographic SAR imaging. Meanwhile, a pixel by pixel orbit baseline estimation method is developed to address the research gaps of baseline estimation for 3D & 4D spaceborne SAR tomography imaging. Moreover, a SAR tomography imaging algorithm and a differential tomography four-dimensional SAR imaging algorithm based on compressive sensing, SAR interferometry phase (InSAR) calibration reference to DEM with DEM error correction, a new phase error calibration and compensation algorithm, based on PS, SVD, PGA, weighted least squares and minimum entropy, are developed to obtain accurate 3D & 4D tomographic SAR imaging results. The new baseline estimation method and consequent TomoSAR processing results showed that an accurate baseline estimation is essential to build up the TomoSAR model. After baseline estimation, phase calibration experiments (via FFT and Capon method) indicate that a phase calibration step is indispensable for TomoSAR imaging, which eventually influences the inversion results. A super-resolution reconstruction CS based study demonstrates X band data with the CS method does not fit for forest reconstruction but works for reconstruction of large civil engineering structures such as dams and urban buildings. Meanwhile, the L band data with FFT, Capon and the CS method are shown to work for the reconstruction of large manmade structures (such as bridges) and urban buildings

Sentinel-1 Support in the GAMMA Software

AbstractFirst results using the new Sentinel-1 SAR look very promising but the special interferometric wide-swath data acquired in the TOPS mode makes InSAR processing more challenging than for normal stripmap mode data. The steep azimuth spectra ramp in each burst results in very stringent co-registration requirements. Combining the data of the individual bursts and sub-swaths into consistent mosaics requires careful “book-keeping” in the handling of the data and meta data and the large file sizes and high data throughputs require also a good performance. Considering these challenges good support from software is getting increasingly important. In this contribution we describe the Sentinel-1 support in the GAMMA Software, a high-level software package used by researchers, service providers and operational users in their SAR, InSAR, PSI and offset tracking work

High-accuracy digital elevation model generation and ship monitoring from synthetic aperture radar images: innovative techniques and experimental results.

In this Thesis several state-of-the-art and innovative techniques for Digital Elevation Model (DEM) generation from Synthetic Aperture Radar (SAR) images are deeply analyzed, with a special focus on the methods which allow the improvement of the accuracy of the DEM product, which is directly related to the geolocation accuracy of geocoded images and is considered as an enabling factor for a large series of civilian and Defence applications. Furthermore, some of the proposed techniques, which are based both on phase and amplitude information, are experimented on real data, i.e. COSMO-SkyMed (CSK) data, assessing the achievable performances compared with the state-of-the-art, and pointing out and quantitatively highlighting the acquisition and processing strategies which would allow to maximize the quality of the results. Moreover, a critical analysis is performed about the main errors affecting the applied techniques, as well as the limitations of the orbital configurations, identifying several complementary techniques which would allow to overcome or mitigate the observed drawbacks. An innovative procedure for on-demand DEM production from CSK SAR data is elaborated and proposed, as well as an auto-validation technique which would enable the validation of the produced DEM also where vertical ground truths are not available. Based on the obtained results and on the consequent critical analysis, several interferometric specifications for new generation SAR satellites are identified. Finally, a literature review is proposed about the main state-of-the-art ship monitoring techniques, considered as one of the main fields of application which takes benefit from SAR data, based on single/multi-platform multi-channel SAR data, with a focus on TanDEM-X (TDX). In particular, in Chapter 1 the main concepts concerning SAR operating principles are introduced and the main characteristics and performances of CSK and TDX satellite systems are described; in Chapter 2 a review is proposed about the state-of-the-art SAR interferometric techniques for DEM generation, analyzing all the relevant processing steps and deepening the study of the main solutions recently proposed in the literature to increase the accuracy of the interferometric processing; in Chapter 3 complementary and innovative techniques respect to the interferometric processing are analyzed to mitigate disadvantages and to improve performances; in Chapter 4 experimental results are presented, obtained in the generation of high accuracy DEM by applying to a dataset of CSK images properly selected state-of-the-art interferometric techniques and innovative methods to improve DEM accuracy, exploring relevant limitations, and pointing out innovative acquisition and processing strategies. In Chapter 5, the basic principles of Ground Moving Target Indication (GMTI) are described, focusing on Displaced Phase Center Antenna (DPCA) and Along-Track Interferometry (ATI) techniques