Technical aspects of Envisat-ASAR geocoding capability at DLR

Based on experience with the geocoding systems for ERS-D-PAF (GEOS), the SIR-C/X-SAR (GEOS) and SRTM missions (GeMoS), geocoding functionality has been extended for Envisat ASAR data. The existing Envisat ASAR Geocoding System (EGEO) can handle all Level 1-b image products (IMS, APS, IMP, APP, IMM, APM, WSM and GM1). Complementary to geocoded products provided by ESA (IMG, APG) the geocoding procedure applied at the German Aerospace Center (DLR) makes use of a DEM to achieve higher geolocation accuracy. The resulting geocoded image is either defined as EEC (Enhanced Ellipsoid Corrected) or as ETC (Enhanced Terrain Corrected). These products mainly differ in the underlying DEM used for geocoding. The EEC utilizes GLOBE, while the ETC utilizes the “best” DEM available in the data base. This “best” DEM can be assembled from different DEM data sets (e.g. derived from SRTM, ERS, …). Further differences such as the interpolative (EEC) and rigorous (ETC) geocoding approach will also be outlined. Furthermore, an incidence angle mask can be generated. The necessary upgrades for geocoding ASAR stripline products (e.g. IMM, WSM) will be presented. Stripline products cover a large area along track, as they consist of concatenated stand-alone products (“slices”). Thus the updates of relevant parameters have to be taken into account

The glaciers climate change initiative: Methods for creating glacier area, elevation change and velocity products

Glaciers and their changes through time are increasingly obtained from a wide range of satellite sensors. Due to the often remote location of glaciers in inaccessible and high-mountain terrain, satellite observations frequently provide the only available measurements. Furthermore, satellite data provide observations of glacier character- istics that are difficult to monitor using ground-based measurements, thus complementing the latter. In the Glaciers_cci project of the European Space Agency (ESA), three of these characteristics are investigated in detail: glacier area, elevation change and surface velocity. We use (a) data from optical sensors to derive glacier outlines, (b) digital elevation models from at least two points in time, (c) repeat altimetry for determining elevation changes, and (d) data from repeat optical and microwave sensors for calculating surface velocity. For the latter, the two sensor types provide complementary information in terms of spatio-temporal coverage. While (c) and (d) can be generated mostly automatically, (a) and (b) require the intervention of an analyst. Largely based on the results of various round robin experiments (multi-analyst benchmark studies) for each of the products, we suggest and describe the most suitable algorithms for product creation and provide recommendations concerning their practical implementation and the required post-processing. For some of the products (area, velocity) post-processing can influence product quality more than the main-processing algorithm

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

Topographic estimation by terrasar-X

SAR Interferometry (InSAR) is a technique to derive Digital Elevation Model (DEM) from at least two complex SAR images. The data are either taken simultaneously (single-pass mode) or sequentially (repeat-pass mode) by airborne or space-born sensors (carriers: plane, satellite, shuttle etc.). To date, one of the most important single-pass interferometry measurement campaigns is the Shuttle Radar Topography Mission (SRTM) completing its mission successfully after 11 days of operation between 11th and 22nd of February 2000. On the other hand, repeat-pass InSAR has been used by several satellite systems: ENVISAT, ERS 1-2, RADARSAT 1-2, ALOS, JERS-1 etc. One of the most advanced systems is the German TerraSAR-X (TSX) satellite launched on June 15th , 2007. TSX offers high resolution (∼1m by Spotlight mode) imagery which could not been achieved from radar technologies up to this time similar to high resolution optical imagery. In contrast to optical sensors, TSX can be operated under all weather conditions without being influenced by clouds. The data sets provided by TSX newly obtained by scientific community and evaluations are currently being performed. As mentioned above, utilizing the advantages of SAR technology, indeed the planimetric locations of target ground objects, elevations of them can be determined using interferometry. Through the interferometric data, interferograms (fringe maps) can be generated and applying interferometric processing steps height models can be created for large coverage interest areas. The main targets of this investigation can be summarized as; generation of height models derived from TSX InSAR image-pairs and evaluation by comparison with more accurate reference height models as well as height models based on high resolution optical satellite images. Absolute and relative accuracy, stability, homogeneity and dependency upon various parameters are determined. The approach will be demonstrated using TSX data covering Istanbul area, Turkey.TUBITAKDL

One Decade of Glacier Mass Changes on the Tibetan Plateau Derived from Multisensoral Remote Sensing Data

The Tibetan Plateau (TP) with an average altitude of 4,500 meters above sea level is characterized by many glaciers and ice caps. Glaciers are a natural indicator for climate variability in this high mountain environment where meteorological stations are rare or non-existent. In addition, the melt water released from the Tibetan glaciers is feeding the headwaters of the major Asian river systems and contributes to the rising levels of endorheic lakes on the plateau. As many people directly rely on the glacier melt water a continuous glacier monitoring program is necessary in this region. In situ measurements of glaciers are important, but are spatial limited due to large logistical efforts, physical constrains and high costs. Remote sensing techniques can overcome this gap and are suitable to complement in situ measurements on a larger scale. In the last decade several remote sensing studies dealt with areal changes of glaciers on the TP. However, glacier area changes only provide a delayed signal to a changing climate and the amount of melt water released from the glaciers cannot be quantified. Therefore it is important to measure the glacier mass balance. In order to estimate glacier mass balances and their spatial differences on the TP, several remote sensing techniques and sensors were synthesized in this thesis. In a first study data from the Ice Cloud and Elevation Satellite (ICESat) mission were employed. ICESat was in orbit between 2003 and 2009 and carried a laser altimeter which recorded highly accurate surface elevation measurements. As in mid-latitudes these measurements are rather sparse glaciers on the TP were grouped into eight climatological homogeneous sub-regions in order to perform a statistical sound analysis of glacier elevation changes. To assess surface elevation changes of a single mountain glacier from ICESat data, an adequate spatial sampling of ICESat measurements need to be present. This is the case for the Grosser Aletschgletscher, located in the Swiss Alps which served as a test site in this thesis. In another study data from the current TanDEM-X satellite mission and from the Shuttle Radar Topography Mission (SRTM) conducted in February 2000 were employed to calculate glacier elevation changes. In a co-authored study, these estimates could be compared with glacier elevation changes obtained from the current French Pléiades satellite mission. In order to calculate glacier mass balances, the derived elevation changes were combined with assumptions about glacier area and ice density in all studies. In this thesis contrasting patterns of glacier mass changes were found on the TP. With an ICESat derived estimate of -15.6±10.1 Gt/a between 2003 and 2009 the average glacier mass balance on the TP was clearly negative. However, some glaciers in the central and north-western part of the TP showed a neutral mass balance or a slightly positive anomaly which was also confirmed by data from the current TanDEM-X satellite mission. A possible explanation of this anomaly in mass balance could be a compensation of the temperature driven glacier melt due to an increase in precipitation

Fusion of Interferometric SAR and Photogrammetric Elevation Data

Neurology & clinical neurophysiolog

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

Identifying areas of neotectonic activity using radar remote sensing in the northern foothills of the Alaska Range

Thesis (M.S.) University of Alaska Fairbanks, 2013The tectonically active northern foothills of the Alaska Range display obvious uplift and deformation, making the area an attractive place to conduct research. Research has been done in this area of Alaska in the recent past, most of which required intensive fieldwork. This study analyzes if modern radar remote sensing technology is useful in identifying neotectonic activity and in determining where future work should be conducted. Radar remote sensing data is used in two ways to support the identification of tectonically active areas: First, I incorporated available geologic maps with polarimetric and interferometric radar remote sensing data to create a classification scheme to identify and map the preserved depositional surface of the Nenana Gravel. This surface, successfully mapped and overlain on a newly available high-resolution DEM, highlighted the topographic expression of deformation in the area. Second, the high-resolution DEMs were used to create and analyze longitudinal river profiles, and a Stream Length-gradient Index Map, both of which correlate well with known active structures. This study indicates that radar remote sensing can be used to identify tectonically active areas before employing extensive fieldwork and used in combination with traditional geological procedures enhances the amount and quality of the derived information