Search

The idea of the former Earth Explorer 10 mission Hydroterra is to place a SAR system into a geosynchronous orbit to understand rapid processes of the diurnal water cycle over regions of interest in Europe and Africa. The DLR Microwaves and Radar Institute conducted an airborne SAR campaign to support the Hydroterra mission. Airborne data were collected to simulate the long integration time of a geosynchronous SAR image and to evaluate the potential to detect diurnal moisture changes. In this paper the airborne campaign is described and the achieved results are presented.

The GeoWAM project aims to achieve high-resolution and highly-accurate digital elevation models (DEM) to monitor the evolution of tidal flats over the German North Sea. To achieve this, the dual-frequency/dual-baseline (DFDB) DEM generation approach, recently developed by DLR, was further expanded to include L-band data. Based in the experience obtained in the 2019 GeoWAM campaign with X- and S-band only, the addition of L-band for the 2020 campaign helps to deal with the decorrelation found in repeat-pass data and potentially allows the creation of new merged products. For the computation of phase and coherence, a new local fringe frequency approach was included to improve the final generated DEMs.

Multi-platform campaigns open up new opportunities and allow a comparison and analysis of SAR signatures of the same area at different frequency bands and incident angles. In this paper, we make use of two different sensor systems: DLR's pulsed F-SAR operating at X-, C- and L-band, and FHR's frequency-modulated continuous-wave (FMCW) MIRANDA35 operating at Ka-band. Main goals of the campaign include the comparison of high-resolution polarimetric signatures at different frequency bands, change detection, synchronized acquisition of ground moving targets and air-moving target indication (AMTI) experiments. We present the planning and implementation of the campaign and first results of the data processing.

An Enceladus mission launched within a realistic time frame (e.g., launch between 2025 and 2040 and a transfer time of about ten years) would likely arrive as the sun is departing or gone from the most interesting South Polar Region marked by its active jets erupting through the ice crust. This almost drives the need for a radar instrument enabling the imaging, mapping and characterization of the moon independent of sunlight illumination. The known ice penetration capability of radar waves in the tens of MHz up to few GHz range allows for the exploration of subsurface features, whereas the surface may be imaged with high level of detail in higher frequencies up to several tens of GHz. In the frame of the Enceladus Explorer Initiative (EnEx) of the German Aerospace Center (DLR), we are currently investigating the potential of a multimodal orbital radar instrument to be used as a companion to a lander mission and to contribute in the understanding of the structure, composition and temporal variation of the Enceladean ice crust and the involved geophysical processes.The considered orbit geometries, strongly constrained by the presence of Saturn, allow for global coverage and offer half-daily revisit of the South Polar Region. We suggest a multi frequency system working concurrently in high frequency (e.g., Ka-band) and lower frequency (e.g., P-band) for surface and subsurface exploration, respectively, both capable of operating in a variety of modes: i) high resolution imaging used as a synthetic aperture radar (SAR), ii) SAR interferometer for topography, permittivity and surface and volume deformation estimates, iii) nadir looking configuration operating as an altimeter for elevation estimates and as a sounder for subsurface exploration with great penetration capability, iv) radiometer for surface temperature estimates and inversion of temperature profiles, and v) bistatic measurements between the radar instrument and an ice penetrating probe deployed by the lander with similarities to the CONSERT instrument of ESA's Rosetta mission.In this presentation, we evaluate the potential of the different modes concerning their scientific output and their usefulness for supporting the success of a lander mission. In particular the performance of SAR imaging and interferometry (single- and repeat-pass) modes are analysed, which are expected to provide key information for landing site selection such as structure, composition and topography of the surface and subsurface with metric resolution. For validation, we present results of a SAR campaign conducted using DLR's airborne sensor F-SAR over an alpine glacier, with simultaneous X- and L-band acquisitions. The campaign incorporates repeat- and single-pass acquisitions, as well as circular flights, which provide interferometric and tomographic measurements with observation geometries similar to those of an Enceladus mission. Furthermore, we provide an analysis towards a bistatic sounding experiment. Utilizing the transmission line between the radar instrument and a transponder integrated in an ice penetrating probe allows for the inversion of the spatial distribution of the dielectric ice properties and associated geophysical parameters (e.g., density, grain size, temperature, and salinity).

Zusammenfassung. Der SKT nach Hellmut Erzigkeit ist ein kurzer Leistungstest zur Erfassung von Störungen des Gedächtnisses und der Aufmerksamkeit. Er wurde mithilfe eines regressionsbasierten Ansatzes nach Zachary und Gorsuch (1985) neunormiert (SKT Edition Manual 2015). Dieses war notwendig geworden, weil zum einen die letzte Normierung leicht veraltet ist, und zum anderen weil Berichte aus der Praxis vermehrt gezeigt haben, dass die alte Normierung im Bereich der beginnenden kognitiven Veränderungen zu ungenau ausfiel. Für die Neunormierung wurden 2 Datensätze verwendet (eine Stichprobe von N = 1 053 gesunden Menschen und eine klinische Stichprobe N = 930 inklusive Demenzdiagnosen). Die Stichprobe gesunder älterer Menschen diente der Berechnung von Soll-Leistungen in den Subtests. Subtrahiert man die gemessene Ist-Leistung einer neuen Testperson von deren Soll-Leistung und teilt diese Differenz durch den Standardfehler der Leistungen einer neuen Testperson (siehe Crawford & Garthwaite, 2006 ), dann entsteht eine t-Verteilung. Diese t-Verteilung ist symmetrisch um den Wert 0 verteilt; die oberen Prozentränge repräsentieren mehr Soll- als Ist-Leistungen (positive Werte für die Differenz). Die unteren Prozentränge repräsentieren schlechte Leistungen, da hier die Ist-Leistung geringer ausfällt als die Soll-Leistung (d. h. es entstehen hier negative Werte für die Differenz zwischen Ist- und Soll-Leistungen). Große negative Differenzen zwischen Ist- und Soll-Leistungen werden mit Abweichungspunkten bewertet und über alle 9 Subtests zu einem SKT-Gesamtwert aufsummiert. Die klinische Stichprobe diente der Ermittlung von Cut-Offs im Rahmen des SKT-Gesamtwertes. Der regressionsbasierte Normierungsansatz wird ausführlich beschrieben und als nützliche Alternative zum klassischen Normierungsansatz dargestellt.

The Microwaves and Radar Institute of the German Aerospace Center (DLR) is known for its consistent work on the field of airborne Synthetic Aperture Radar and its application. Currently, the Institute is developing a new advanced airborne SAR system, the DBFSAR, which is planned to supplement its operational F-SAR system in near future. The development of DBFSAR was triggered by the various evolving digital beamforming (DBF) techniques for future spaceborne SAR systems and the need for an airborne experimental platform for preparation of such missions. Additionally, there is a demand for very high resolution SAR imagery, which cannot anymore be fully satisfied with the existing F-SAR system. This paper should give an overview over the current status and performance of the DBFSAR system, including first results from its maiden flight in November 2016.

The F-SAR instrument represents DLR’s advanced airborne SAR testbed for technology and remote sensing applications. The development of the instrument was triggered by a strong demand for data being simultaneously acquired at different wavelengths and polarizations as well as by the demand for very high range resolution. F-SAR is a modular development utilizing modern hardware and commercial of the shelf components. For the purpose of experiments and operational data acquisition campaigns the system is being installed on board a DLR Dornier DO228 research aircraft. This paper gives an overview of the instrument’s capabilities and performance, based on the multi-frequency and fully polarimetric imagery acquired during campaigns in the last two years. More specifically, campaigns in Greenland in 2015 (ARCTIC) and Gabon in 2016 (AfriSAR) are presented.

Zu den Standardaufgaben von Arzten und Arztinnen in Gesundheitsamtern gehort seit jeher die Entwicklungsdiagnostik von Kindern. Angesichts der zunehmenden Anzahl von dementiellen Erkrankungen in Deutschland ruckt eine Entwicklungsdiagnostik im Alter starker in den Mittelpunkt. Eine solche Diagnostik gibt Auskunft daruber, ob die untersuchte Person sich unauffallig und altersentsprechend entwickelt oder ob die in der Untersuchung erzielten kognitiven Leistungen Hinweise auf einen pathologischen (dementiellen) Prozess geben. Es werden 2 Tests zur Erfassung von kognitiven Leistungen im Alter vorgestellt: die Wechsler Adult Intelligence Scale (WAIS-IV) und der Syndrom-Kurztest (SKT), ein Test zur Erfassung von Gedachtnis- und Aufmerksamkeitsstorungen. Ferner werden Ubereinstimmungen und Unterschiede zwischen beiden Verfahren beschrieben. Im Rahmen einer multizentrischen Studie im deutschsprachigen Raum wurden Daten von 504 kognitiv unauffalligen Probanden im Alter von 60 bis 90 mit der WAIS-IV und dem SKT erhoben und ausgewertet. Die Ergebnisse deuten darauf hin, dass mit zunehmenden Alter sowohl kognitive Leistungen der fluiden als auch der kristallinen Intelligenz signifikant abnehmen. In nur 2 Untertests des WAIS-IV gab es keine signifikanten Mittelwertunterschiede in Abhangigkeit des Alters (Allgemeines Wissen und Mosaik Test). Die SKT-Scores zum Gedachtnis und Aufmerksamkeit korrelierten signifikant mit fast allen Untertestes des WAIS. Am starksten korrelierten die SKT-Aufmerksamkeitscores mit den Untertests zur Verarbeitungsgeschwindigkeit (VG), Wahrnehmungsgebundenes Logisches Denken (WLD) und Arbeitsgedachtnis (AG). Verantwortlich fur den kognitiven Abbau sind in erster Linie Verminderungen in der Verarbeitungsgeschwindigkeit sowie beim Arbeitsgedachtnis.

Im Rahmen der Entwicklungsdiagnostik im Alter wird gezeigt, wie man unauffällige kognitive Leistungen von pathologischen Abbauprozessen unterscheiden kann. Dies geschieht mit dem regressionsbasierten Normierungsansatz nach Zachary und Gorsuch (1985) . Die Analysen basieren auf Daten einer Multicenter-Studie von N = 349 älteren gesunden Probanden zwischen 60 und 90 Jahren, die mit dem SKT nach Erzigkeit (1989) , einem Leistungstest zur Erfassung von Gedächtnis- und Aufmerksamkeitsstörungen, und zwei Untertests aus der WAIS-IV ( Petermann, 2012 ), dem Matrizentest (MT) und dem Wortschatz-Test (WT) getestet wurden. Es zeigten sich sowohl für den MT als auch den WT signifikante Mittelwertsunterschiede in Abhängigkeit vom Alter, die einen signifikanten Abbau der intellektuellen Fähigkeiten dokumentieren. Die kognitiven Leistungen im Alter hingen signifikant mit der Verarbeitungsgeschwindigkeit sowie wenn auch weniger stark ausgeprägt, mit der Gedächtnisleistung zusammen. Die Ergebnisse des regressionsnormierten Ansatzes scheinen einen bedeutsamen Beitrag zur Entwicklungsdiagnostik im Alter leisten zu können.

AfriSAR is an ESA-funded airborne P-band SAR campaign over the African tropical forests of Gabon that is being carried out by ONERA (July 2015) and DLR (February 2016) in support of the development of the geophysical algorithms of the future BIOMASS mission. Multibaseline fully-polarimetric acquisitions have been designed over four test sites in order to further develop and validate algorithms for the estimation of forest upper canopy height, 3-D structure and biomass by implementing PolSAR (SAR Polarimetry), Pol-InSAR (Polarimetric SAR Interferometry) and TomoSAR (SAR Tomography) P-band measurements. In this paper first data processing results will be shown.

The design and test of 5-way high power divider operating at P-band for the airborne Synthetic Aperture Radar (SAR) system of DLR is presented. Distinctive features are high bandwidth, high power and an unequal power split on the 5 output ports.

The objective of the NASA Soil Moisture Active & Passive (SMAP) mission is to provide global measurements of soil moisture and its freeze/thaw state. The SMAP measurement approach is to integrate L-band radar and radiometer as a single observation system combining the respective strengths of active and passive remote sensing for enhanced soil moisture mapping. Airborne instruments will be a key part of the SMAP validation program. Here, we present an airborne campaign in the Rur catchment, Germany, in which the passive L-band system Polarimetric L-band Multi-beam Radiometer (PLMR2) and the active L-band system DLR F-SAR were flown on six dates in 2013. The flights covered the full heterogeneity of the area under investigation, i.e. all types of land cover and experimental monitoring sites. The obtained data sets are used as a test-bed for the analysis of existing and development of new active-passive fusion techniques.

The Microwaves and Radar Institute at the German Aerospace Center operate an airborne multi-frequency, polarimetric, imaging SAR system. The F-SAR sensor is equipped with a variety of different antennas, based on patch technology. A new antenna element is developed for the P-Band frequency range from 400 to 470 MHz. Due to the requirements of the aircraft the size of the antenna array and therefore of each single element, is reduced to a minimum. A cavity backed, capacitively coupled stacked patch element is designed and presented in this paper.

During the last decade, synthetic aperture radar (SAR) became an indispensable source of information in Earth observation. This has been possible mainly due to the current trend toward higher spatial resolution and novel imaging modes. A major driver for this development has been and still is the airborne SAR technology, which is usually ahead of the capabilities of spaceborne sensors by several years. Today's airborne sensors are capable of delivering high-quality SAR data with decimeter resolution and allow the development of novel approaches in data analysis and information extraction from SAR. In this paper, a review about the abilities and needs of today's very high-resolution airborne SAR sensors is given, based on and summarizing the longtime experience of the German Aerospace Center (DLR) with airborne SAR technology and its applications. A description of the specific requirements of high-resolution airborne data processing is presented, followed by an extensive overview of emerging applications of high-resolution SAR. In many cases, information extraction from high-resolution airborne SAR imagery has achieved a mature level, turning SAR technology more and more into an operational tool. Such abilities, which are today mostly limited to airborne SAR, might become typical in the next generation of spaceborne SAR missions.

The F-SAR airborne SAR instrument represents the successor of the E-SAR system of the German Aerospace Center (DLR), which had previously been extensively used over the last three decades. Its development was triggered by the current demand for simultaneous acquisitions at different wavelengths and polarisations as well as by the demand for very high resolution in the order of decimetres. F-SAR is a modular development utilising state of the art hardware. As for E-SAR, DLRs Dornier DO228-212 aircraft is the first choice as platform for the new system. With the recently completed X-band single-pass interferometer and the P-band subsystem, F-SAR is now ready for fully replacing the E-SAR. This paper presents the two new subsystems and analyses their performance based on fully polarimetric imagery acquired during recent system test and calibration campaigns.

The objective of the NASA Soil Moisture Active & Passive (SMAP) mission is to provide global measurements of soil moisture by fused active and passive L-band microwave measurements. With an airborne campaign conducted in the Rur catchment, Germany, in 2012, an active and passive L-band microwave data set is generated. The passive Polarimetric L-band Multi-beam Radiometer (PLMR2) and the active L-band system DLR F-SAR were installed on the DLR Dornier DO 228 aircraft. Despite of the differences between the airborne and the future spaceborne sensors, the data set will serve as a test bed for the analysis of existing and development of enhanced future active/passive data fusion techniques. Moreover, the derivation of (vegetation) parameters for the fusion approaches is planned.

Launched in June 2010, TanDEM-X is an interferometric mission with the main goal of providing a high-resolution, global and unprecedentedly accurate digital elevation model (DEM) of the Earth by means of single-pass X-band SAR interferometry. Despite its usual quasi-monostatic configuration, TanDEM-X is the first genuinely bistatic SAR system in space. During its monostatic commissioning phase, the system was operated in pursuit monostatic mode. During that time, some pioneering bistatic SAR experiments with both satellites commanded in non-nominal modes were conducted with the main purpose of testing the performance of both space and ground segments in very demanding scenarios. In particular, this article includes results of the first bistatic acquisition and the first single-pass interferometric (mono/bistatic) acquisition with TanDEM-X, addressing their innovative aspects and focussing on the analysis of the experimental results. Even in the absence of essential synchronisation and calibration information, bistatic images and interferogramswith similar quality to pursuit monostatic have been obtained. Some months later, with TanDEM-X already in its operational DEM-acquisition phase a further challenging bistatic acquisition carried out in cooperation with DLR's airborne radar F-SAR has been carried out. The objective was to acquire fully polarimetric interferometric data with a high range of available bistatic angles. A dedicated commanding of both TanDEM-X and F-SAR was required, including irregular sampling schemes, partially missing bistatic echo reception and bistatic synchronisation, which pose a number of technological challenges in SAR data processing before the calibrated bistatic SAR images are obtained. This article reports about these two set of experiments.

A Compact Test Range (CTR) facility shall extend the measurement capabilities at the Microwaves and Radar Institute of the German Aerospace Center (DLR) in Oberpfaffenhofen. Today's accuracy requirements in the RF-component characterization are decisive factors for the specification of a new measurement facility. Parts of a Compact Antenna Test Range (CATR) model 8074B, manufactured by March Microwave Systems B.V., have been purchased by the Institute in 2006. On the basis of these components, a compact test range in a new building named ‘HF-TechLab’ is currently under construction. It is planned to be operational at the end of 2009. An overview of the entire CTR facility is the objective of this paper.

The F-SAR airborne SAR instrument represents the successor of the E-SAR system of the German Aerospace Center (DLR), which has been extensively used in the last three decades. Its development was triggered by the current demand for data being simultaneously acquired at different wavelengths and polarisations as well as by the demand for very high resolution in the order of decimetres. F-SAR is a modular development utilising the most modern hardware and commercial off the shelf components. As for E-SAR DLRs Dornier DO228-212 aircraft is the first choice as platform for the new system. Although the F-SAR system is still under development, it is already taking over some of the operational duties of the old E-SAR system. This paper will analyse the performance of the current system, based on the multi-frequency and fully polarimetric imagery acquired during several campaigns in the last two years. Since F-SAR is using a fixed antenna mount without gimbal, precise radiometric calibration is particularly challenging, especially in the shorter wavelengths. Therefore, special emphasis is placed on the system calibration and the associated quality control including the achieved spatial resolution and radiometric accuracy in the different bands.

A Compact Test Range (CTR) facility shall extend the measurement capabilities at the Microwaves and Radar Institute of the German Aerospace Center (DLR) in Oberpfaffenhofen. Today’s accuracy requirements in the RF-component characterization are decisive factors for the specification of a new measurement facility. Parts of a Compact Antenna Test Range (CATR) model 8074B, manufactured by March Microwave Systems B.V., have been purchased by the Institute in 2006. On the basis of these components, a compact test range in a new building named ‘HF-TechLab’ is currently under construction. It is planned to be operational at the end of 2009. An overview of the entire CTR facility is the objective of this paper.

In this paper a reflectarray design for a membrane spaceborne antenna to be used in a typical SAR mission is presented. An L-Band reflectarray, with a dimension of 10 by 6 meters on Kapton foil substrate, has been designed. To evaluate the tolerance to the membrane deformations, a model for the surface wrinkles and sag is developed and their effects on the antenna performance are analyzed. Finally, a full-wave numerical analysis has been performed and the result are presented.

Following the success of the first bistatic spaceborne-airborne experiment between TerraSAR-X and F-SAR carried out in November 2007, DLR has performed a second bistatic experiment in July 2008 with new challenging acquisitions. Furthermore, the existing bistatic processing chain has been updated with two significant improvements: a) clock offset synchronisation is now performed without the use of reference targets, and b) SAR imaging is done using a fast focussing technique. The new SAR imaging algorithm, based on the fast factorised backprojection algorithm, has proved very good focussing qualities while dramatically reducing (up to a factor 100 with respect to direct backprojection) the overall computational load. The new processing chain is tested using the image of the first TerraSAR-X experiment. Results of a dualpol acquisition performed during the second TerraSAR-X/F-SAR experiment and showing the first dual-pol bistatic spaceborne-airborne images are also presented in this paper.

Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination board, a spaceborne-airborne bistatic experiment was successfully performed early November 2007. TSX was used as transmitter and DLR's new airborne radar system, F-SAR, as receiver; due to the capability of the latter to acquire data quasi-continuously, no echo window synchronisation is needed. Monostatic data were also recorded during the acquisition. This paper includes description and results of the spaceborne-airborne bistatic experiment, with special focus on data processing and image comparison. Given the acquisition scenario, with two-channel sampling and transmitter and receiver clocks operating independently, data processing must necessarily follow a three-step strategy: 1) channel balancing, 2) data synchronisation and 3) bistatic SAR processing. Since neither absolute range nor Doppler references are available in the bistatic data set, synchronisation is done with the help of calibration targets on ground and based on the analysis of the acquired data compared to expected data. Due to the variant nature of the bistatic acquisition and the required precision for the processing, data are processed using a bistatic backprojection approach.