Special Issue "Ten Years of TerraSAR-X—Scientific Results"

A special issue of Remote Sensing (ISSN 2072-4292).

Deadline for manuscript submissions: closed (30 April 2018).

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. Michael Eineder
E-Mail Website
Guest Editor
DLR, Remote Sensing Technology Institute, Muenchener Str. 20, Wessling, D-82234, Germany
Interests: SAR interferometry; InSAR; geodetic SAR; digital elevation models; SAR applications
Mr. Achim Roth
E-Mail Website
Guest Editor
DLR, Remote Sensing Data Center DFD, Muenchener Str. 20, Wessling, D-82234, Germany
Interests: SAR applications; digital elevation models
Prof. Dr. Alberto Moreira
E-Mail Website
Guest Editor
DLR, Microwaves and Radar Institute, Muenchener Str. 20, Wessling, D-82234, Germany
Tel. +49 8153 28-2306
Interests: SAR technology; SAR missions; SAR applications

Special Issue Information

Dear Colleagues,

In the year 2017 we are looking back on 10 years of reliable TerraSAR-X operations. This X-band synthetic aperture radar (SAR) satellite offered for the first time very-high-resolution radar imagery from space with extreme geometric accuracy on the centimeter level, outstanding interferometric capabilities, different polarizations, and experimental imaging modes such as an along-track interferometry mode (ATI), a quad-pol mode, and recently a starring spotlight and a wide ScanSAR mode.

TerraSAR-X was launched in the scope of a public–private partnership between the German Aerospace Center (DLR) and Airbus Defence and Space. While DLR is responsible for data reception and archive, data processing and calibration, as well as for promoting and coordinating research with the data, Airbus has developed the satellites and takes over the commercial data exploitation. In 2010, TerraSAR-X was followed by its sister satellite. When both are operated in bi-static interferometric configuration, they form the TanDEM-X mission.

Thanks to its high resolution and the precise revisit geometry, TerraSAR-X opened new capabilities for many applications. For example, the monitoring of highly structured urban areas was significantly improved even down to the level of single buildings and infrastructure such as bridges. The position of individual scatterers can be determined with sub-meter precision by interferometric and tomographic methods. Repeat-pass interferometry revealed relative deformation even within buildings or infrastructure.

In ocean applications, TerraSAR-X shows details of wave patterns unresolved so far. Small ships can be detected, and even their type classified. In the cryosphere, glacier velocities could be determined all year round by feature tracking thanks to the high resolution and the geometric accuracy. Additionally, the understanding of small-scale landslides or the dynamics of volcanos benefit from the high spatial and temporal resolution of an X-band system.

In the last 10 years, the geometric accuracy has been pushed to the maximum by means of novel correction methods and calibration procedures. Today, TerraSAR-X has an unprecedented geometric accuracy, capable of pin-pointing objects in 3D space within a 5-cm cube, making it a most precise geodetic imaging sensor in space.

In this call for a special issue “Ten Years of TerraSAR-X – Scientific Results”, we expect contributions on new scientific results covering methods and applications as well as overview papers on topics such as

  • high-resolution deformation measurements,
  • urban tomography,
  • urban mapping applications,
  • geodetic applications
  • cryosphere applications,
  • agriculture and forestry,
  • ocean applications,
  • and others.

The submission of overview papers should be coordinated with the editors to avoid overlapping and conflicts.

We especially welcome papers that exploit the 10-year continuity of data and the worldwide coverage.

Note that this Special Issue will not address the TanDEM-X mission (i.e. methods and applications that are focused on applications related to digital elevation models and use bi-static or pursuit-monostatic data). We plan to coordinate another special issue on TanDEM-X soon.

Authors are required to check and follow the specific instructions to authors at https://www.mdpi.com/journal/remotesensing/instructions

Prof. Dr. Michael Eineder
Mr. Achim Roth
Prof. Dr. Alberto Moreira
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (21 papers)

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Editorial

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Open AccessEditorial
Ten Years of TerraSAR-X—Scientific Results
Remote Sens. 2019, 11(3), 364; https://doi.org/10.3390/rs11030364 - 11 Feb 2019
Abstract
This special issue is a collection of papers addressing the scientific utilization of data acquired in the course of the TerraSAR-X mission. The articles deal with the mission itself, the accuracy of the products, with differential interferometry, and with applications in the domains [...] Read more.
This special issue is a collection of papers addressing the scientific utilization of data acquired in the course of the TerraSAR-X mission. The articles deal with the mission itself, the accuracy of the products, with differential interferometry, and with applications in the domains cryosphere, oceans, wetlands, and urban areas. This editorial summarizes the content. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available

Research

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Open AccessArticle
Development of Operational Applications for TerraSAR-X
Remote Sens. 2018, 10(10), 1535; https://doi.org/10.3390/rs10101535 - 25 Sep 2018
Cited by 1
Abstract
In the course of the TerraSAR-X mission, various new applications based on X-Band Synthetic Aperture Radar (SAR) data have been developed and made available as operational products or services. In this article, we elaborate on proven characteristics of TerraSAR-X that are responsible for [...] Read more.
In the course of the TerraSAR-X mission, various new applications based on X-Band Synthetic Aperture Radar (SAR) data have been developed and made available as operational products or services. In this article, we elaborate on proven characteristics of TerraSAR-X that are responsible for development of operational applications. This article is written from the perspective of a commercial data and service provider and the focus is on the following applications with high commercial relevance, and varying operational maturity levels: Surface Movement Monitoring (SMM), Ground Control Point (GCP) extraction and Automatic Target Recognition (ATR). Based on these applications, the article highlights the successful transition of innovative research into sustainable and operational use within various market segments. TerraSAR-X’s high orbit accuracy, its precise radar beam tracing, the high-resolution modes, and high-quality radiometric performance have proven to be the instrument’s advanced characteristics, through, which reliable ground control points and surface movement measurements are obtained. Moreover, TerraSAR-X high-resolution data has been widely exploited for the clarity of its target signatures in the fields of target intelligence and identification. TerraSAR-X’s multi temporal interferometry applications are non-invasive and are now fully standardised autonomous tools to measure surface deformation. In particular, multi-baseline interferometric techniques, such as Persistent Scatter Interferometry (PSI) and Small Baseline Subsets (SBAS) benefit from TerraSAR-X’s highly precise orbit information and phase stability. Similarly, the instrument’s precise orbit information is responsible for sub-metre accuracy of Ground Control Points (GCPs), which are essential inputs for orthorectification of remote sensing imagery, to locate targets, and to precisely georeference a variety of datasets. While geolocation accuracy is an essential ingredient in the intelligence field, high-resolution TerraSAR-X data, particularly in Staring SpotLight mode has been widely used in surveillance, security and reconnaissance applications in real-time and also by automatic or assisted target recognition software. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Mitigation of Tropospheric Delay in SAR and InSAR Using NWP Data: Its Validation and Application Examples
Remote Sens. 2018, 10(10), 1515; https://doi.org/10.3390/rs10101515 - 21 Sep 2018
Cited by 3
Abstract
The neutral atmospheric delay has a great impact on synthetic aperture radar (SAR) absolute ranging and on differential interferometry. In this paper, we demonstrate its effective mitigation by means of the direction integration method using two products from the European Centre for Medium-Range [...] Read more.
The neutral atmospheric delay has a great impact on synthetic aperture radar (SAR) absolute ranging and on differential interferometry. In this paper, we demonstrate its effective mitigation by means of the direction integration method using two products from the European Centre for Medium-Range Weather Forecast: ERA-Interim and operational data. Firstly, we shortly review the modeling of the neutral atmospheric delay for the direct integration method, focusing on the different refractivity models and constant coefficients available. Secondly, a thorough validation of the method is performed using two approaches. In the first approach, numerical weather prediction (NWP) derived zenith path delay (ZPD) is validated against ZPD from permanent GNSS (global navigation satellite system) stations on a global scale, demonstrating a mean accuracy of 14.5 mm for ERA-Interim. Local analysis shows a 1 mm improvement using operational data. In the second approach, NWP derived slant path delay (SPD) is validated against SAR SPD measured on corner reflectors in more than 300 TerraSAR-X High Resolution SpotLight acquisitions, demonstrating an accuracy in the centimeter range for both ERA-Interim and operational data. Finally, the application of this accurate delay estimate for the mitigation of the impact of the neutral atmosphere on SAR absolute ranging and on differential interferometry, both for individual interferograms and multi-temporal processing, is demonstrated. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Land Subsidence in Coastal Environments: Knowledge Advance in the Venice Coastland by TerraSAR-X PSI
Remote Sens. 2018, 10(8), 1191; https://doi.org/10.3390/rs10081191 - 29 Jul 2018
Cited by 4
Abstract
The use of satellite SAR interferometric methods has significantly improved the monitoring of ground movements over the last decades, thus opening new possibilities for a more accurate interpretation of land subsidence and its driving mechanisms. TerraSAR-X has been extensively used to study land [...] Read more.
The use of satellite SAR interferometric methods has significantly improved the monitoring of ground movements over the last decades, thus opening new possibilities for a more accurate interpretation of land subsidence and its driving mechanisms. TerraSAR-X has been extensively used to study land subsidence in the Venice Lagoon, Italy, with the aim of quantifying the natural and anthropogenic causes. In this paper, we review and update the main results achieved by three research projects supported by DLR AOs (German Aerospace Center Announcement of Opportunity) and conducted to test the capability of TerraSAR-X PSI (Persistent Scatterer Interferometry) to detect ground movements in the complex physiographic setting of the Venice transitional coastal environment. The investigations have been focused on the historical center of Venice, the lagoon inlets where the MoSE is under construction, salt marshes, and newly built-up areas in the littoral. PSI on stacks of stripmap TerraSAR-X images covering short- to long-time periods (i.e., the years 2008–2009, 2008–2011 and 2008–2013) has proven particularly effective to measure land subsidence in the Venice coastland. The very high spatial resolution (3 m) and the short repeat time interval (11 days) of the TerraSAR-X acquisitions make it possible to investigate ground movements with a detail unavailable in the past. The interferometric products, properly calibrated, allowed for a millimetric vertical accuracy of the land movements at both the regional and local scales, even for short-term analyses, i.e., spanning one year only. The new picture of the land movement resulted from processing TerraSAR-X images has significantly contributed to update the knowledge on the subsidence process at the Venice coast. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
TerraSAR-X Time Series Fill a Gap in Spaceborne Snowmelt Monitoring of Small Arctic Catchments—A Case Study on Qikiqtaruk (Herschel Island), Canada
Remote Sens. 2018, 10(7), 1155; https://doi.org/10.3390/rs10071155 - 21 Jul 2018
Cited by 2
Abstract
The timing of snowmelt is an important turning point in the seasonal cycle of small Arctic catchments. The TerraSAR-X (TSX) satellite mission is a synthetic aperture radar system (SAR) with high potential to measure the high spatiotemporal variability of snow cover extent (SCE) [...] Read more.
The timing of snowmelt is an important turning point in the seasonal cycle of small Arctic catchments. The TerraSAR-X (TSX) satellite mission is a synthetic aperture radar system (SAR) with high potential to measure the high spatiotemporal variability of snow cover extent (SCE) and fractional snow cover (FSC) on the small catchment scale. We investigate the performance of multi-polarized and multi-pass TSX X-Band SAR data in monitoring SCE and FSC in small Arctic tundra catchments of Qikiqtaruk (Herschel Island) off the Yukon Coast in the Western Canadian Arctic. We applied a threshold based segmentation on ratio images between TSX images with wet snow and a dry snow reference, and tested the performance of two different thresholds. We quantitatively compared TSX- and Landsat 8-derived SCE maps using confusion matrices and analyzed the spatiotemporal dynamics of snowmelt from 2015 to 2017 using TSX, Landsat 8 and in situ time lapse data. Our data showed that the quality of SCE maps from TSX X-Band data is strongly influenced by polarization and to a lesser degree by incidence angle. VH polarized TSX data performed best in deriving SCE when compared to Landsat 8. TSX derived SCE maps from VH polarization detected late lying snow patches that were not detected by Landsat 8. Results of a local assessment of TSX FSC against the in situ data showed that TSX FSC accurately captured the temporal dynamics of different snow melt regimes that were related to topographic characteristics of the studied catchments. Both in situ and TSX FSC showed a longer snowmelt period in a catchment with higher contributions of steep valleys and a shorter snowmelt period in a catchment with higher contributions of upland terrain. Landsat 8 had fundamental data gaps during the snowmelt period in all 3 years due to cloud cover. The results also revealed that by choosing a positive threshold of 1 dB, detection of ice layers due to diurnal temperature variations resulted in a more accurate estimation of snow cover than a negative threshold that detects wet snow alone. We find that TSX X-Band data in VH polarization performs at a comparable quality to Landsat 8 in deriving SCE maps when a positive threshold is used. We conclude that TSX data polarization can be used to accurately monitor snowmelt events at high temporal and spatial resolution, overcoming limitations of Landsat 8, which due to cloud related data gaps generally only indicated the onset and end of snowmelt. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Remote Sensing of Organic Films on the Water Surface Using Dual Co-Polarized Ship-Based X-/C-/S-Band Radar and TerraSAR-X
Remote Sens. 2018, 10(7), 1097; https://doi.org/10.3390/rs10071097 - 10 Jul 2018
Cited by 5
Abstract
Microwave radar is a well-established tool for all-weather monitoring of film slicks which appear in radar imagery of the surface of water bodies as areas of reduced backscatter due to suppression of short wind waves. Information about slicks obtained with single-band/one-polarized radar seems [...] Read more.
Microwave radar is a well-established tool for all-weather monitoring of film slicks which appear in radar imagery of the surface of water bodies as areas of reduced backscatter due to suppression of short wind waves. Information about slicks obtained with single-band/one-polarized radar seems to be insufficient for film characterization; hence, new capabilities of multi-polarization radars for monitoring of film slicks have been actively discussed in the literature. In this paper the results of new experiments on remote sensing of film slicks using dual co-polarized radars—a satellite TerraSAR-X and a ship-based X-/C-/S-band radar—are presented. Radar backscattering is assumed to contain Bragg and non-Bragg components (BC and NBC, respectively). BC is due to backscattering from resonant cm-scale wind waves, while NBC is supposed to be associated with wave breaking. Each of the components can be eliminated from the total radar backscatter measured at two co-polarizations, and contrasts of Bragg and non-Bragg components in slicks can be analyzed separately. New data on a damping ratio (contrast) characterizing reduction of radar returns in slicks are obtained for the two components of radar backscatter in various radar bands. The contrast values for Bragg and non-Bragg components are comparable to each other and demonstrate similar dependence on radar wave number; BC and NBC contrasts grow monotonically for the cases of upwind and downwind observations and weakly decrease with wave number for the cross-wind direction. Reduction of BC in slicks can be explained by enhanced viscous damping of cm-scale Bragg waves due to an elastic film. Physical mechanisms of NBC reduction in slicks are discussed. It is hypothesized that strong breaking (e.g., white-capping) weakly contributes to the NBC contrast because of “cleaning” of the water surface due to turbulent surfactant mixing associated with wave crest overturning. An effective mechanism of NBC reduction due to film can be associated with modification of micro-breaking wave features, such as parasitic ripples, bulge, and toe, in slicks. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Remote Sensing Intertidal Flats with TerraSAR-X. A SAR Perspective of the Structural Elements of a Tidal Basin for Monitoring the Wadden Sea
Remote Sens. 2018, 10(7), 1085; https://doi.org/10.3390/rs10071085 - 07 Jul 2018
Cited by 4
Abstract
Spatial distribution and dynamics of intertidal habitats are integral elements of the Wadden Sea ecosystem, essential for the preservation of ecosystem functions and interlocked with geomorphological processes. Protection and monitoring of the Wadden Sea is mandatory and remote sensing is required to survey [...] Read more.
Spatial distribution and dynamics of intertidal habitats are integral elements of the Wadden Sea ecosystem, essential for the preservation of ecosystem functions and interlocked with geomorphological processes. Protection and monitoring of the Wadden Sea is mandatory and remote sensing is required to survey the extensive, often inaccessible tidal area. Mainly airborne techniques are carried out for decades. High-resolution satellite-borne sensors now enable new possibilities with satellite synthetic aperture radar (SAR) offering high availability of acquisitions during low water time due to independence from daylight and cloud cover. More than 100 TerraSAR-X images from 2009 to 2016 were used to examine the reproduction of intertidal habitats and macrostructures from the flats south of the island of Norderney and comparative areas in the Lower Saxony Wadden Sea. As a non-specific, generic approach to distinguish various and variable surface types continuously influenced by tidal dynamics, visual analysis was chosen which was supported by extensive in situ data. This technically unsophisticated access enabled us to identify mussel beds, fields of shell-detritus, gully structures, mud fields, and bedforms, the latter detected in the upper flats of every East Frisian island. Based on the high frequency of TerraSAR-X recordings for the Norderney area, a bedform shift was observed in a time-series from 2009 to 2015. For the same period, the development of a mud field with an adjoining depression was traced. Beside seasonal variations of the mud field, the formation of a mussel bed settling in the depression was imaged over the years. This study exemplifies the relevance of TerraSAR-X imagery for Wadden Sea remote sensing. Further development of classification methods for current SAR data together with open access availability should contribute to large-scale surveys of intertidal surface structures of geomorphic or biogenic origin and improve monitoring and long-term ecological research in the Wadden Sea and related tidal areas. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
A New InSAR Phase Demodulation Technique Developed for a Typical Example of a Complex, Multi-Lobed Landslide Displacement Field, Fels Glacier Slide, Alaska
Remote Sens. 2018, 10(7), 995; https://doi.org/10.3390/rs10070995 - 22 Jun 2018
Cited by 1
Abstract
Landslides can have complex, spatially strongly inhomogeneous surface displacement fields with discontinuities from multiple active lobes that are deforming while failing on nested slip surfaces at different depths. For synthetic aperture radar interferometry (InSAR), particularly at lower resolutions, these characteristics can cause significant [...] Read more.
Landslides can have complex, spatially strongly inhomogeneous surface displacement fields with discontinuities from multiple active lobes that are deforming while failing on nested slip surfaces at different depths. For synthetic aperture radar interferometry (InSAR), particularly at lower resolutions, these characteristics can cause significant aliasing of the wrapped phase. In combination with steep terrain and seasonal snow cover, causing layover and temporal decorrelation, respectively, traditional phase unwrapping can become unfeasible, even after topographic phase contributions have been removed with an external high-resolution digital surface model (DSM). We present a novel method: warp demodulation that reduces the complexity of the phase unwrapping problem for noisy and/or aliased, low-resolution interferograms of discontinuous landslide displacement. The key input to our warp demodulation method is a single (or several) reference interferogram(s) from a high-resolution sensor mode such as TerraSAR-X Staring Spotlight with short temporal baseline and good coherence to allow localization of phase discontinuities and accurate unwrapping. The task of constructing suitable phase surfaces to approximate individual to-be-demodulated interferograms from the reference interferogram is made difficult by strong and spatially inhomogeneous temporal, seasonal, and interannual variations of the landslide with individual lobes accelerating or decelerating at different rates. This prevents using simple global scaling of the reference. Instead, our method uses an irregular grid of small patches straddling strong spatial gradients and phase discontinuities in the reference to find optimum local scaling factors that minimize the residual phase gradients across the discontinuities after demodulation. Next, for each to-be-demodulated interferogram, from these measurements we interpolate a spatially smooth global scaling function, which is then used to scale the (discontinuous) reference. Demodulation with the scaled reference leads to a residual phase that is also spatially smooth, allowing it to be unwrapped robustly after low-pass filtering. A key assumption of warp demodulation is that the locations of the phase discontinuities can be mapped in the reference and that they are stationary in time at the scale of the image resolution. We carry out extensive tests with simulated data to establish the accuracy, robustness, and limitations of the new method with respect to relevant parameters, such as decorrelation noise and aliasing along phase discontinuities. A realistic parameterization of the method is demonstrated for the example of the Fels Glacier Slide in Alaska using a recent late-summer high-resolution staring spotlight interferometric image pair from TerraSAR-X to demodulate. We show warp demodulation results for also recent but early-summer, partially incoherent interferograms of the same sensor, as well as for older and coarser aliased interferograms from RADARSAT-2, ALOS-1, and ERS. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessFeature PaperArticle
Assessing Single-Polarization and Dual-Polarization TerraSAR-X Data for Surface Water Monitoring
Remote Sens. 2018, 10(6), 949; https://doi.org/10.3390/rs10060949 - 14 Jun 2018
Cited by 2
Abstract
Three synthetic aperture radar (SAR) data classification methodologies were used to assess the ability of single-polarization and dual-polarization TerraSAR-X (TSX) data to classify surface water, including open water, ice, and flooded vegetation. Multi-polarization SAR observations contain more information than single-polarization SAR, but the [...] Read more.
Three synthetic aperture radar (SAR) data classification methodologies were used to assess the ability of single-polarization and dual-polarization TerraSAR-X (TSX) data to classify surface water, including open water, ice, and flooded vegetation. Multi-polarization SAR observations contain more information than single-polarization SAR, but the availability of multi-polarization data is much lower, which limits the temporal monitoring capabilities. The study area is a principally natural landscape centered on a seasonally flooding river, in which four TSX dual-co-polarized images were acquired between the months of April and June 2016. Previous studies have shown that single-polarization SAR is useful for analyzing surface water extent and change using grey-level thresholding. The H-Alpha–Wishart decomposition, adapted to dual-polarization data, and the Kennaugh Element Framework were used to classify areas of water and flooded vegetation. Although grey-level thresholding was able to identify areas of water and non-water, the percentage of seasonal change was limited, indicating an increase in water area from 8% to 10%, which is in disagreement with seasonal trends. The dual-polarization methods show a decrease in water over the season and indicate a decrease in flooded vegetation, which agrees with expected seasonal variations. When comparing the two dual-polarization methods, a clear benefit of the Kennaugh Elements Framework is the ability to classify change in the transition zones of ice to open water, open water to marsh, and flooded vegetation to land, using the differential Kennaugh technique. The H-Alpha–Wishart classifier was not able to classify ice, and misclassified fields and ice as water. Although single-polarization SAR was effective in classifying open water, the findings of this study confirm the advantages of dual-polarization observations, with the Kennaugh Element Framework being the best performing classification framework. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Landslide Monitoring Using Multi-Temporal SAR Interferometry with Advanced Persistent Scatterers Identification Methods and Super High-Spatial Resolution TerraSAR-X Images
Remote Sens. 2018, 10(6), 921; https://doi.org/10.3390/rs10060921 - 11 Jun 2018
Cited by 5
Abstract
Landslides are one of the most common and dangerous threats in the world that generate considerable damage and economic losses. An efficient landslide monitoring tool is the Differential Synthetic Aperture Radar Interferometry (DInSAR) or Persistent Scatter Interferometry (PSI). However, landslides are usually located [...] Read more.
Landslides are one of the most common and dangerous threats in the world that generate considerable damage and economic losses. An efficient landslide monitoring tool is the Differential Synthetic Aperture Radar Interferometry (DInSAR) or Persistent Scatter Interferometry (PSI). However, landslides are usually located in mountainous areas and the area of interest can be partially or even heavily vegetated. The inherent temporal decorrelation that dramatically reduces the number of Persistent Scatters (PSs) of the scene limits in practice the application of this technique. Thus, it is crucial to be able to detect as much PSs as possible that can be usually embedded in decorrelated areas. High resolution imagery combined with efficient pixel selection methods can make possible the application of DInSAR techniques in landslide monitoring. In this paper, different strategies to identify PS Candidates (PSCs) have been employed together with 32 super high-spatial resolution (SHR) TerraSAR-X (TSX) images, staring-spotlight mode, to monitor the Canillo landslide (Andorra). The results show that advanced PSI strategies (i.e., the temporal sub-look coherence (TSC) and temporal phase coherence (TPC) methods) are able to obtain much more valid PSs than the classical amplitude dispersion (DA) method. In addition, the TPC method presents the best performance among all three full-resolution strategies employed. The SHR TSX data allows for obtaining much higher densities of PSs compared with a lower-spatial resolution SAR data set (Sentinel-1A in this study). Thanks to the huge amount of valid PSs obtained by the TPC method with SHR TSX images, the complexity of the structure of the Canillo landslide has been highlighted and three different slide units have been identified. The results of this study indicate that the TPC approach together with SHR SAR images can be a powerful tool to characterize displacement rates and extension of complex landslides in challenging areas. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Where We Live—A Summary of the Achievements and Planned Evolution of the Global Urban Footprint
Remote Sens. 2018, 10(6), 895; https://doi.org/10.3390/rs10060895 - 07 Jun 2018
Cited by 7
Abstract
The TerraSAR-X (TSX) mission provides a distinguished collection of high resolution satellite images that shows great promise for a global monitoring of human settlements. Hence, the German Aerospace Center (DLR) has developed the Urban Footprint Processor (UFP) that represents an operational framework for [...] Read more.
The TerraSAR-X (TSX) mission provides a distinguished collection of high resolution satellite images that shows great promise for a global monitoring of human settlements. Hence, the German Aerospace Center (DLR) has developed the Urban Footprint Processor (UFP) that represents an operational framework for the mapping of built-up areas based on a mass processing and analysis of TSX imagery. The UFP includes functionalities for data management, feature extraction, unsupervised classification, mosaicking, and post-editing. Based on >180.000 TSX StripMap scenes, the UFP was used in 2016 to derive a global map of human presence on Earth in a so far unique spatial resolution of 12 m per grid cell: the Global Urban Footprint (GUF). This work provides a comprehensive summary of the major achievements related to the Global Urban Footprint initiative, with dedicated sections focusing on aspects such as UFP methodology, basic product characteristics (specification, accuracy, global figures on urbanization derived from GUF), the user community, and the already initiated future roadmap of follow-on activities and products. The active community of >250 institutions already working with the GUF data documents the relevance and suitability of the GUF initiative and the underlying high-resolution SAR imagery with respect to the provision of key information on the human presence on earth and the global human settlements properties and patterns, respectively. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Internal Solitary Waves in the Andaman Sea: New Insights from SAR Imagery
Remote Sens. 2018, 10(6), 861; https://doi.org/10.3390/rs10060861 - 01 Jun 2018
Cited by 3
Abstract
The Andaman Sea in the Indian Ocean has been a classical study region for Internal Solitary Waves (ISWs) for several decades. Papers such as Osborne and Burch (1980) usually describe mode-1 packets of ISWs propagating eastwards, separated by distances of around 100 km. [...] Read more.
The Andaman Sea in the Indian Ocean has been a classical study region for Internal Solitary Waves (ISWs) for several decades. Papers such as Osborne and Burch (1980) usually describe mode-1 packets of ISWs propagating eastwards, separated by distances of around 100 km. In this paper, we report on shorter period solitary-like waves that are consistent with a mode-2 vertical structure, which are observed along the Ten Degree Channel, and propagate side-by-side the usual large mode-1 solitary wave packets. The mode-2 waves are identified in TerraSAR-X images because of their distinct surface signatures, which are reversed when compared to those that are typical of mode-1 ISWs in the ocean. These newly observed regularly-spaced packets of ISW-like waves are characterized by average separations of roughly 30 km, which are far from the nominal mode-1 or even the mode-2 internal tidal wavelengths. On some occasions, five consecutive and regularly spaced mode-2 ISW-like wave envelopes were observed simultaneously in the same TerraSAR-X image. This fact points to a tidal generation mechanism somewhere in the west shallow ridges, south of the Nicobar Islands. Furthermore, it implies that unusually long-lived mode-2 waves can be found throughout the majority of the fortnightly tidal cycle. Ray tracing techniques are used to identify internal tidal beams as a possible explanation for the generation of the mode-2 solitary-like waves when the internal tidal beam interacts with the ocean pycnocline. Linear theory suggests that resonant coupling with long internal waves of higher-mode could explain the longevity of the mode-2 waves, which propagate for more than 100 km. Owing to their small-scale dimensions, the mode-2 waves may have been overlooked in previous remote sensing images. The enhanced radiometric resolution of the TerraSAR-X, alongside its wide coverage and detailed spatial resolutions, make it an ideal observational tool for the present study. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Staring Spotlight TerraSAR-X SAR Interferometry for Identification and Monitoring of Small-Scale Landslide Deformation
Remote Sens. 2018, 10(6), 844; https://doi.org/10.3390/rs10060844 - 28 May 2018
Cited by 2
Abstract
We discuss enhanced processing methods for high resolution Synthetic Aperture Radar
(SAR) interferometry (InSAR) to monitor small landslides with difficult spatial characteristics,
such as very steep and rugged terrain, strong spatially heterogeneous surface motion,
and coherence-compromising factors, including vegetation and seasonal snow cover.
[...] Read more.
We discuss enhanced processing methods for high resolution Synthetic Aperture Radar
(SAR) interferometry (InSAR) to monitor small landslides with difficult spatial characteristics,
such as very steep and rugged terrain, strong spatially heterogeneous surface motion,
and coherence-compromising factors, including vegetation and seasonal snow cover. The enhanced
methods mitigate phase bias induced by atmospheric effects, as well as topographic phase errors
in coherent regions of layover, and due to inaccurate blending of high resolution discontinuous
with lower resolution background Digital Surface Models (DSM). We demonstrate the proposed
methods using TerraSAR-X (TSX) Staring Spotlight InSAR data for three test sites reflecting diverse
challenging landslide-prone mountain terrains in British Columbia, Canada. Comparisons with
corresponding standard processing methods show significant improvements with resulting
displacement residuals that reveal additional movement hotspots and unprecedented spatial detail
for active landslides/rockfalls at the investigated sites.

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(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Combining TerraSAR-X and Landsat Images for Emergency Response in Urban Environments
Remote Sens. 2018, 10(5), 802; https://doi.org/10.3390/rs10050802 - 21 May 2018
Cited by 3
Abstract
Rapid damage mapping following a disaster event, especially in an urban environment, is critical to ensure that the emergency response in the affected area is rapid and efficient. This work presents a new method for mapping damage assessment in urban environments. Based on [...] Read more.
Rapid damage mapping following a disaster event, especially in an urban environment, is critical to ensure that the emergency response in the affected area is rapid and efficient. This work presents a new method for mapping damage assessment in urban environments. Based on combining SAR and optical data, the method is applicable as support during initial emergency planning and rescue operations. The study focuses on the urban areas affected by the Tohoku earthquake and subsequent tsunami event in Japan that occurred on 11 March 2011. High-resolution TerraSAR-X (TSX) images of before and after the event, and a Landsat 5 image before the event were acquired. The affected areas were analyzed with the SAR data using only one interferometric SAR (InSAR) coherence map. To increase the damage mapping accuracy, the normalized difference vegetation index (NDVI) was applied. The generated map, with a grid size of 50 m, provides a quantitative assessment of the nature and distribution of the damage. The damage mapping shows detailed information about the affected area, with high overall accuracy (89%), and high Kappa coefficient (82%) and, as expected, it shows total destruction along the coastline compared to the inland region. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Long-Term Validation of TerraSAR-X and TanDEM-X Orbit Solutions with Laser and Radar Measurements
Remote Sens. 2018, 10(5), 762; https://doi.org/10.3390/rs10050762 - 15 May 2018
Cited by 3
Abstract
Precise orbit determination solutions for the two spacecrafts TerraSAR-X (TSX) and TanDEM-X (TDX) are operationally computed at the German Space Operations Center (GSOC/DLR). This publication makes use of 6 years of TSX and TDX orbit solutions for a detailed orbit validation. The validation [...] Read more.
Precise orbit determination solutions for the two spacecrafts TerraSAR-X (TSX) and TanDEM-X (TDX) are operationally computed at the German Space Operations Center (GSOC/DLR). This publication makes use of 6 years of TSX and TDX orbit solutions for a detailed orbit validation. The validation compares the standard orbit products with newly determined enhanced orbit solutions, which additionally consider GPS ambiguity fixing and utilize a macro model for modeling non-gravitational forces. The technique of satellite laser ranging (SLR) serves as a key measure for validating the derived orbit solutions. In addition, the synthetic aperture radar (SAR) instruments on-board both spacecrafts are for the first time employed for orbit validation. Both the microwave instrument and the optical laser approach are compared and assessed. The average SLR residuals, obtained from the TSX and TDX enhanced orbit solutions within the analysis period, are at 1.6 ± 11.4 mm ( 1 σ ) and 1.2 ± 12.5 mm, respectively. Compared to the standard orbit products, this is an improvement of 33 % in standard deviation. The corresponding radar range biases are in the same order and amount to 3.5 ± 12.5 mm and 4.5 ± 14.9 mm. Along with the millimeter level position offsets in radial, along-track and cross-track inferred from the SLR data on a monthly basis, the results confirm the advantage of the enhanced orbit solutions over the standard orbit products. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Radiometric Performance of the TerraSAR-X Mission over More Than Ten Years of Operation
Remote Sens. 2018, 10(5), 754; https://doi.org/10.3390/rs10050754 - 15 May 2018
Cited by 2
Abstract
The TerraSAR-X mission, based on two satellites, has produced SAR data products of high quality for a number of scientific and commercial applications for more than ten years. To guarantee the stability and the reliability of these highly accurate SAR data products, both [...] Read more.
The TerraSAR-X mission, based on two satellites, has produced SAR data products of high quality for a number of scientific and commercial applications for more than ten years. To guarantee the stability and the reliability of these highly accurate SAR data products, both systems were first accurately calibrated during their respective commissioning phases and have been permanently monitored since then. Based on a short description of the methods applied, this paper focuses on the radiometric performance including the gain and phase properties of the transmit/receiver modules, the antenna pattern checked by evaluating scenes acquired over uniformly distributed targets and the radiometric stability derived from permanently deployed point targets. The outcome demonstrates the remarkable performance of both systems since their respective launch. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessArticle
Measurements on the Absolute 2-D and 3-D Localization Accuracy of TerraSAR-X
Remote Sens. 2018, 10(4), 656; https://doi.org/10.3390/rs10040656 - 23 Apr 2018
Cited by 6
Abstract
The German TerraSAR-X radar satellites TSX-1 and TDX-1 are well-regarded for their unprecedented geolocation accuracy. However, to access their full potential, Synthetic Aperture Radar (SAR)-based location measurements have to be carefully corrected for effects that are well-known in the area of geodesy but [...] Read more.
The German TerraSAR-X radar satellites TSX-1 and TDX-1 are well-regarded for their unprecedented geolocation accuracy. However, to access their full potential, Synthetic Aperture Radar (SAR)-based location measurements have to be carefully corrected for effects that are well-known in the area of geodesy but were previously often neglected in the area of SAR, such as wave propagation and Earth dynamics. Our measurements indicate that in this way, when SAR is handled as a geodetic measurement instrument, absolute localization accuracy at better than centimeter level with respect to a given geodetic reference frame is obtained in 2-D and, when using stereo SAR techniques, also in 3-D. The TerraSAR-X measurement results presented in this study are based on a network of three globally distributed geodetic observatories. Each is equipped with one or two trihedral corner reflectors with accurately (<5 mm) known reference coordinates, used as a reference for the verification of the SAR measured coordinates. Because these observatories are located in distant parts of the world, they give us evidence on the worldwide reproducibility of the obtained results. In this paper we report the achieved results of measurements performed over 6 1/2 years (from July 2011 to January 2018) and refer to some first new application areas for geodetic SAR. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Review

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Open AccessReview
A Review of Ten-Year Advances of Multi-Baseline SAR Interferometry Using TerraSAR-X Data
Remote Sens. 2018, 10(9), 1374; https://doi.org/10.3390/rs10091374 - 30 Aug 2018
Cited by 7
Abstract
Since its launch in 2007, TerraSAR-X has continuously provided spaceborne synthetic aperture radar (SAR) images of our planet with unprecedented spatial resolution, geodetic, and geometric accuracy. This has brought life to the once inscrutable SAR images, which deterred many researchers. Thanks to merits [...] Read more.
Since its launch in 2007, TerraSAR-X has continuously provided spaceborne synthetic aperture radar (SAR) images of our planet with unprecedented spatial resolution, geodetic, and geometric accuracy. This has brought life to the once inscrutable SAR images, which deterred many researchers. Thanks to merits like higher spatial resolution and more precise orbit control, we are now able to indicate individual buildings, even individual floors, to pinpoint targets within centimeter accuracy. As a result, multi-baseline SAR interferometric (InSAR) techniques are flourishing, from point target-based algorithms, to coherent stacking techniques, to absolute positioning of the former techniques. This article reviews the recent advances of multi-baseline InSAR techniques using TerraSAR-X images. Particular focus was put on our own development of persistent scatterer interferometry, SAR tomography, robust estimation in distributed scatterer interferometry and absolute positioning using geodetic InSAR. Furthermore, by introducing the applications associated with these techniques, such as 3D reconstruction and deformation monitoring, this article is also intended to give guidance to wider audiences who would like to resort to SAR data and related techniques for their applications. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessReview
Ten Years of Experience with Scientific TerraSAR-X Data Utilization
Remote Sens. 2018, 10(8), 1170; https://doi.org/10.3390/rs10081170 - 24 Jul 2018
Cited by 2
Abstract
This paper presents the first comprehensive review on the scientific utilization of earth observation data provided by the German TerraSAR-X mission. It considers the different application fields and technical capabilities to identify the key applications and the preferred technical capabilities of this high-resolution [...] Read more.
This paper presents the first comprehensive review on the scientific utilization of earth observation data provided by the German TerraSAR-X mission. It considers the different application fields and technical capabilities to identify the key applications and the preferred technical capabilities of this high-resolution SAR satellite system from a scientific point of view. The TerraSAR-X mission is conducted in a close cooperation with industry. Over the past decade, scientists have gained access to data through a proposal submission and evaluation process. For this review, we have considered 1636 data utilization proposals and analyzed 2850 publications. In general, TerraSAR-X data is used in a wide range of geoscientific research areas comprising anthroposphere, biosphere, cryosphere, geosphere, and hydrosphere. Methodological and technical research is a cross-cutting issue that supports all geoscientific fields. Most of the proposals address research questions concerning the geosphere, whereas the majority of the publications focused on research regarding “methods and techniques”. All geoscientific fields involve systematic observations for the establishment of time series in support of monitoring activities. High-resolution SAR data are mainly used for the determination and investigation of surface movements, where SAR interferometry in its different variants is the predominant technology. However, feature tracking techniques also benefit from the high spatial resolution. Researchers make use of polarimetric SAR capabilities, although they are not a key feature of the TerraSAR-X system. The StripMap mode with three meter spatial resolution is the preferred SAR imaging mode, accounting for 60 percent of all scientific data acquisitions. The Spotlight modes with the highest spatial resolution of less than one meter are requested by only approximately 30 percent of the newly acquired TerraSAR-X data. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessReview
TerraSAR-X and Wetlands: A Review
Remote Sens. 2018, 10(6), 916; https://doi.org/10.3390/rs10060916 - 10 Jun 2018
Cited by 5
Abstract
Since its launch in 2007, TerraSAR-X observations have been widely used in a broad range of scientific applications. Particularly in wetland research, TerraSAR-X’s shortwave X-band synthetic aperture radar (SAR) possesses unique capabilities, such as high spatial and temporal resolution, for delineating and characterizing [...] Read more.
Since its launch in 2007, TerraSAR-X observations have been widely used in a broad range of scientific applications. Particularly in wetland research, TerraSAR-X’s shortwave X-band synthetic aperture radar (SAR) possesses unique capabilities, such as high spatial and temporal resolution, for delineating and characterizing the inherent spatially and temporally complex and heterogeneous structure of wetland ecosystems and their dynamics. As transitional areas, wetlands comprise characteristics of both terrestrial and aquatic features, forming a large diversity of wetland types. This study reviews all published articles incorporating TerraSAR-X information into wetland research to provide a comprehensive study of how this sensor has been used with regard to polarization, and the function of the data, time-series analyses, or the assessment of specific wetland ecosystem types. What is evident throughout this literature review is the synergistic fusion of multi-frequency and multi-polarization SAR sensors, sometimes optical sensors, in almost all investigated studies to attain improved wetland classification results. Due to the short revisiting time of the TerraSAR-X sensor, it is possible to compute dense SAR time-series, allowing for a more precise observation of the seasonality in dynamic wetland areas as demonstrated in many of the reviewed studies. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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Open AccessReview
Ten Years of TerraSAR-X Operations
Remote Sens. 2018, 10(6), 873; https://doi.org/10.3390/rs10060873 - 05 Jun 2018
Cited by 5
Abstract
The satellite of the TerraSAR-X mission, called TSX, was launched on 15 June 2007 and its identically constructed twin satellite TDX, which is required by the mission TanDEM-X, launched on 21 June 2010. Together they supply high-quality radar data in order to serve [...] Read more.
The satellite of the TerraSAR-X mission, called TSX, was launched on 15 June 2007 and its identically constructed twin satellite TDX, which is required by the mission TanDEM-X, launched on 21 June 2010. Together they supply high-quality radar data in order to serve two mission goals: Scientific observation of Earth and the provisioning of remote sensing data for the commercial market (TerraSAR-X mission) and the generation of a global digital elevation model (DEM) of Earth’s surface (TanDEM-X mission). On the occasion of the 10th anniversary of the mission, the focus will be on the development of the TerraSAR-X system during this period, including the extension of the ground segment, the evolution of the product portfolio, dedicated mission campaigns, radar experiments, refinement of the satellite operations and orbit control, and the results of the performance monitoring. Despite numerous interventions in the overall system, we managed to incorporate new scientific and commercial requirements and to improve and enhance the overall system in order to fulfill the increasing demand for Earth observation data without noticeable interruptions to ongoing operations. Full article
(This article belongs to the Special Issue Ten Years of TerraSAR-X—Scientific Results) Printed Edition available
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