Direction-of-arrival (DOA) angle estimation is a prerequisite for projecting the airborne radar-b... more Direction-of-arrival (DOA) angle estimation is a prerequisite for projecting the airborne radar-based target detections to ground via a geocoding operation. Most state-ofthe-art DOA angle estimation methods assume one detection per target. These methods cannot be applied one-to-one on extended targets like ships because individual ships in high-resolution data are generally composed of several distinct radar detections. In this letter, four methods for estimating the DOA angle for extended targets are formulated and discussed. The performance of the proposed methods is assessed by using simultaneously acquired automatic identification system (AIS) data of real ships. Radar data from the DLR's multichannel airborne digital beamforming synthetic aperture radar (DBFSAR) system are used to demonstrate the robustness and applicability of the proposed methods in real maritime scenarios.
Road surface roughness is a major factor that is responsible for the skid resistance of vehicles ... more Road surface roughness is a major factor that is responsible for the skid resistance of vehicles and, thus, road safety. Therefore, it needs to be monitored regularly to ensure that the roughness values are in the optimal range and to perform maintenance actions when needed. Synthetic aperture radar (SAR) backscatter is sensitive to surface roughness and can provide large-scale estimates of road surface roughness. In this letter, a semiempirical model for estimating road surface roughness using high-resolution spaceborne X-band SAR datasets from Germany's TerraSAR-X (TS-X) satellite is proposed for the first time. The method is capable of handling the low signal-tonoise ratio (SNR) of spaceborne SAR. To enhance the reliability of the results obtained from rather low SNR datasets, techniques, such as SNR thresholding, multi-dataset fusion, and automatic road extraction, were implemented. The study's results show good agreement with ground-truth (GT) data.
ABSTRACT This document is the output of Task 1 of the ESA Ka-band GMTI study. It provides a revie... more ABSTRACT This document is the output of Task 1 of the ESA Ka-band GMTI study. It provides a review of state-of-the-art single- and multi-channel techniques and algorithms for ground moving target indication and ocean current measurements, and a review of state-of-theart instruments. An analysis of these techniques and algorithms in terms target detection performance, computational load requirements, downlink data rates and need for training sequences is conducted. For each reviewed algorithm the advantages and drawbacks are identified. Potential scenarios of application are listed.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015
ABSTRACT This paper explores the ground moving target indication (GMTI) capabilities of the Germa... more ABSTRACT This paper explores the ground moving target indication (GMTI) capabilities of the German Aerospace Center’s state-of-the-art airborne (F-SAR) and spaceborne (TerraSAR-X) synthetic aperture radars (SARs) when operating over maritime scenarios. The performance of classical dual channel GMTI techniques, such as displaced phase center antenna (DPCA) and along-track interferometry (ATI), as well as the promising adaptive techniques, like extended DPCA (EDPCA) and imaging space–time adaptive processing (ISTAP) have been analyzed on the basis of experimental acquisitions with both sensors. The objective of the paper is to highlight the limitations and challenges to be considered when processing real, multichannel GMTI data from pioneering SAR sensors for maritime surveillance. Different calibration or channel balancing strategies, on the basis of the digital balancing (DB) method, are studied, considering their impact on SAR-GMTI performance. An adaptive SAR processor, accounting for target kinematics and based on a matched filter bank (MFB) approach, is integrated in the SAR-GMTI processing chain in order to retrieve refocused images of the moving vessels.
In the paper a ground moving target indication (GMTI) and parameter estimation algorithm based on... more In the paper a ground moving target indication (GMTI) and parameter estimation algorithm based on a priori knowledge is presented. This algorithm is suitable for real time airborne traffic monitoring applications using single- as well as multi-channel synthetic aperture radar (SAR). It operates directly on range-compressed data. Only the intersection points of the moving vehicle signals with the road axis
In the paper first ground moving target indication (GMTI) and parameter estimation results obtain... more In the paper first ground moving target indication (GMTI) and parameter estimation results obtained with the spaceborne TerraSAR-X/TanDEM-X satellite constellation are presented and discussed. For processing a dual-platform GMTI algorithm developed by the authors was used. This algorithm enables the estimation of the true geographical positions, the velocities and the headings of the detected targets with high accuracy. The algorithm is verified and evaluated using ground truth reference data.
ABSTRACT In this paper an extension of our “Fast GMTI Algorithm for Traffic Monitoring Based on A... more ABSTRACT In this paper an extension of our “Fast GMTI Algorithm for Traffic Monitoring Based on A Priori Knowledge” [1,2] to an arbitrary number of M receiving (RX) channels is presented. This is done by incorporating Post-Doppler space-time adaptive processing into the processing chain. In contrast to our original dual-channel algorithm this additionally allows for robust estimation of the direction-of-arrival (DOA) angles of the detected signals. As a consequence false detections can be recognized and discarded. In the paper the processing chain is explained and performance estimation results for DLR's multi-channel airborne F-SAR system are presented and discussed.
Abstract Following the success of the first bistatic spaceborne-airborne experiment between Terra... more Abstract 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 ...
2012 IEEE International Geoscience and Remote Sensing Symposium, 2012
ABSTRACT This paper presents an initial analysis of the possibilities for velocity and accelerati... more ABSTRACT This paper presents an initial analysis of the possibilities for velocity and acceleration measurement with the Bi-Directional (BiDi) SAR imaging mode. The analysis comprises single satellite single path acquisitions as well as one path of a constellation of two satellites. The translational velocity components into azimuth and range directions are simulated for TerraSAR-X parameters. Image examples show velocity and acceleration effects on ships in the Singapore harbor area acquired with the TerraSAR-X (TSX) and TanDEM-X (TDX) satellites. Special attention is given to interferometric fringes observed on anchoring ships after the subtraction of the surface related phase component. A first approach into the understanding of rotational effects was achieved by the simulation of a rotating ship which resulted in a similar fringe pattern as observed in the interferogram.
| During the last decade, synthetic aperture radar (SAR) became an indispensable source of inform... more | 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.
In the paper a method for along-track velocity estimation of moving targets is presented. This me... more In the paper a method for along-track velocity estimation of moving targets is presented. This method exploits the along-track interferometric (ATI) phase ramp of a range compressed moving target signal between two or more receiving channels. The slope of this phase ramp is mainly influenced by the along-track velocity but not by accelerations. Hence, acceleration independent along-track velocity estimation is feasible. A verification of the proposed method is performed by using both simulations and real two-and four-channel X-band data acquired with DLR's E-SAR and F-SAR system.
This paper reports on several experiments performed by the TanDEM-X constellation that could be p... more This paper reports on several experiments performed by the TanDEM-X constellation that could be potentially implemented as operational modes in future SAR missions. Many of them have been already demonstrated experimentally and could be repeated during a possible next pursuit monostatic phase with TanDEM-X. The new modes include new single-look products as well as interferometric ones, some of which are included in this paper as an example of their potential performance.
TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is an innovative formation flying... more TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is an innovative formation flying radar mission that opens a new era in spaceborne radar remote sensing. The primary objective is the acquisition of a global Digital Elevation Model (DEM) with unprecedented accuracy (12 m horizontal and 2 m vertical resolution). This goal is achieved by extending the TerraSAR-X synthetic aperture radar (SAR) mission by a second, TerraSAR-X like satellite (TDX) flying in close formation with TerraSAR-X (TSX). Both satellites form together a large singlepass SAR interferometer with the opportunity for flexible baseline selection. This enables the acquisition of highly accurate cross-track interferograms without the inherent accuracy limitations imposed by repeat-pass interferometry due to temporal decorrelation and atmospheric disturbances. Besides the primary goal of the mission, several secondary mission objectives based on along-track interferometry as well as new bistatic and multistatic SAR techniques have been defined, representing an important and innovative asset of the TanDEM-X mission. TanDEM-X is implemented in the framework of a public-private partnership between the German Aerospace Center (DLR) and EADS Astrium GmbH. The TanDEM-X mission was successfully launched in June 2010 and started operational data acquisition in December 2010. This paper provides an overview of the TanDEM-X mission and summarizes its actual status and performance. Furthermore, results from several scientific radar experiments are presented that show the great potential of future formation flying interferometric SAR missions to serve novel remote sensing applications.
Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination boa... more Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination board, a spaceborneairborne 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.
ABSTRACT In the paper the usability of LTE data transmission from an aircraft to the ground is in... more ABSTRACT In the paper the usability of LTE data transmission from an aircraft to the ground is investigated. Theoretical analyses and experimental measurements have been carried out by using a commercial low-cost LTE modem and the existing LTE base station infrastructure on ground. In the airborne experiment over wide areas a stable LTE connection was achieved.
Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination boa... more Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination board, a spaceborneairborne 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.
Since November 2006, DLR operates F-SAR - a new airborne SAR sensor beside its experimental airbo... more Since November 2006, DLR operates F-SAR - a new airborne SAR sensor beside its experimental airborne SAR sensor E-SAR. F-SAR is a totally new development utilizing most modern hardware. It is presently operated in X-band and has been supplemented recently being fully polarimetric. F-SAR already accomplished several flights and acquired SAR data in different operation modes, amongst others in along-track-interferometric
To meet the challenges of ever increasing road traffic and the associated economic and sociologic... more To meet the challenges of ever increasing road traffic and the associated economic and sociological impacts, new techniques and technologies for better traffic management are needed. The TRAMRAD project (Traffic Monitoring with space-based Radar) aims to profit from research and development in earth observation and advances in radar remote sensing techniques to define a future space-based sensor system for the
IEEE Transactions on Geoscience and Remote Sensing, 2000
We report about the first X-band spaceborneairborne bistatic synthetic aperture radar (SAR) exper... more We report about the first X-band spaceborneairborne bistatic synthetic aperture radar (SAR) experiment, conducted early November 2007, using the German satellite TerraSAR-X as transmitter and the German Aerospace Center's (DLR) new airborne radar system F-SAR as receiver. The importance of the experiment resides in both its pioneering character and its potential to serve as a test bed for the validation of nonstationary bistatic acquisitions, novel calibration and synchronization algorithms, and advanced imaging techniques. Due to the independent operation of the transmitter and receiver, an accurate synchronization procedure was needed during processing to make high-resolution imaging feasible. Precise phase-preserving bistatic focusing can only be achieved if time and phase synchronization exist. The synchronization approach, based on the evaluation of the range histories of several reference targets, was verified through a separate analysis of the range and Doppler contributions. After successful synchronization, nonstationary focusing was performed using a bistatic backprojection algorithm. During the campaign, stand-alone TerraSAR-X monostatic as well as interoperated TerraSAR-X/F-SAR bistatic data sets were recorded. As expected, the bistatic image shows a space-variant behavior in spatial resolution and in signal-to-noise ratio. Due to the selected configuration, the bistatic image outperforms its monostatic counterpart in almost the complete imaged scene. A detailed comparison between monostatic and bistatic images is given, illustrating the complementarity of both measurements in terms of backscatter and Doppler information. The results are of fundamental importance for the development of future nonsynchronized bistatic SAR systems.
Direction-of-arrival (DOA) angle estimation is a prerequisite for projecting the airborne radar-b... more Direction-of-arrival (DOA) angle estimation is a prerequisite for projecting the airborne radar-based target detections to ground via a geocoding operation. Most state-ofthe-art DOA angle estimation methods assume one detection per target. These methods cannot be applied one-to-one on extended targets like ships because individual ships in high-resolution data are generally composed of several distinct radar detections. In this letter, four methods for estimating the DOA angle for extended targets are formulated and discussed. The performance of the proposed methods is assessed by using simultaneously acquired automatic identification system (AIS) data of real ships. Radar data from the DLR's multichannel airborne digital beamforming synthetic aperture radar (DBFSAR) system are used to demonstrate the robustness and applicability of the proposed methods in real maritime scenarios.
Road surface roughness is a major factor that is responsible for the skid resistance of vehicles ... more Road surface roughness is a major factor that is responsible for the skid resistance of vehicles and, thus, road safety. Therefore, it needs to be monitored regularly to ensure that the roughness values are in the optimal range and to perform maintenance actions when needed. Synthetic aperture radar (SAR) backscatter is sensitive to surface roughness and can provide large-scale estimates of road surface roughness. In this letter, a semiempirical model for estimating road surface roughness using high-resolution spaceborne X-band SAR datasets from Germany's TerraSAR-X (TS-X) satellite is proposed for the first time. The method is capable of handling the low signal-tonoise ratio (SNR) of spaceborne SAR. To enhance the reliability of the results obtained from rather low SNR datasets, techniques, such as SNR thresholding, multi-dataset fusion, and automatic road extraction, were implemented. The study's results show good agreement with ground-truth (GT) data.
ABSTRACT This document is the output of Task 1 of the ESA Ka-band GMTI study. It provides a revie... more ABSTRACT This document is the output of Task 1 of the ESA Ka-band GMTI study. It provides a review of state-of-the-art single- and multi-channel techniques and algorithms for ground moving target indication and ocean current measurements, and a review of state-of-theart instruments. An analysis of these techniques and algorithms in terms target detection performance, computational load requirements, downlink data rates and need for training sequences is conducted. For each reviewed algorithm the advantages and drawbacks are identified. Potential scenarios of application are listed.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015
ABSTRACT This paper explores the ground moving target indication (GMTI) capabilities of the Germa... more ABSTRACT This paper explores the ground moving target indication (GMTI) capabilities of the German Aerospace Center’s state-of-the-art airborne (F-SAR) and spaceborne (TerraSAR-X) synthetic aperture radars (SARs) when operating over maritime scenarios. The performance of classical dual channel GMTI techniques, such as displaced phase center antenna (DPCA) and along-track interferometry (ATI), as well as the promising adaptive techniques, like extended DPCA (EDPCA) and imaging space–time adaptive processing (ISTAP) have been analyzed on the basis of experimental acquisitions with both sensors. The objective of the paper is to highlight the limitations and challenges to be considered when processing real, multichannel GMTI data from pioneering SAR sensors for maritime surveillance. Different calibration or channel balancing strategies, on the basis of the digital balancing (DB) method, are studied, considering their impact on SAR-GMTI performance. An adaptive SAR processor, accounting for target kinematics and based on a matched filter bank (MFB) approach, is integrated in the SAR-GMTI processing chain in order to retrieve refocused images of the moving vessels.
In the paper a ground moving target indication (GMTI) and parameter estimation algorithm based on... more In the paper a ground moving target indication (GMTI) and parameter estimation algorithm based on a priori knowledge is presented. This algorithm is suitable for real time airborne traffic monitoring applications using single- as well as multi-channel synthetic aperture radar (SAR). It operates directly on range-compressed data. Only the intersection points of the moving vehicle signals with the road axis
In the paper first ground moving target indication (GMTI) and parameter estimation results obtain... more In the paper first ground moving target indication (GMTI) and parameter estimation results obtained with the spaceborne TerraSAR-X/TanDEM-X satellite constellation are presented and discussed. For processing a dual-platform GMTI algorithm developed by the authors was used. This algorithm enables the estimation of the true geographical positions, the velocities and the headings of the detected targets with high accuracy. The algorithm is verified and evaluated using ground truth reference data.
ABSTRACT In this paper an extension of our “Fast GMTI Algorithm for Traffic Monitoring Based on A... more ABSTRACT In this paper an extension of our “Fast GMTI Algorithm for Traffic Monitoring Based on A Priori Knowledge” [1,2] to an arbitrary number of M receiving (RX) channels is presented. This is done by incorporating Post-Doppler space-time adaptive processing into the processing chain. In contrast to our original dual-channel algorithm this additionally allows for robust estimation of the direction-of-arrival (DOA) angles of the detected signals. As a consequence false detections can be recognized and discarded. In the paper the processing chain is explained and performance estimation results for DLR's multi-channel airborne F-SAR system are presented and discussed.
Abstract Following the success of the first bistatic spaceborne-airborne experiment between Terra... more Abstract 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 ...
2012 IEEE International Geoscience and Remote Sensing Symposium, 2012
ABSTRACT This paper presents an initial analysis of the possibilities for velocity and accelerati... more ABSTRACT This paper presents an initial analysis of the possibilities for velocity and acceleration measurement with the Bi-Directional (BiDi) SAR imaging mode. The analysis comprises single satellite single path acquisitions as well as one path of a constellation of two satellites. The translational velocity components into azimuth and range directions are simulated for TerraSAR-X parameters. Image examples show velocity and acceleration effects on ships in the Singapore harbor area acquired with the TerraSAR-X (TSX) and TanDEM-X (TDX) satellites. Special attention is given to interferometric fringes observed on anchoring ships after the subtraction of the surface related phase component. A first approach into the understanding of rotational effects was achieved by the simulation of a rotating ship which resulted in a similar fringe pattern as observed in the interferogram.
| During the last decade, synthetic aperture radar (SAR) became an indispensable source of inform... more | 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.
In the paper a method for along-track velocity estimation of moving targets is presented. This me... more In the paper a method for along-track velocity estimation of moving targets is presented. This method exploits the along-track interferometric (ATI) phase ramp of a range compressed moving target signal between two or more receiving channels. The slope of this phase ramp is mainly influenced by the along-track velocity but not by accelerations. Hence, acceleration independent along-track velocity estimation is feasible. A verification of the proposed method is performed by using both simulations and real two-and four-channel X-band data acquired with DLR's E-SAR and F-SAR system.
This paper reports on several experiments performed by the TanDEM-X constellation that could be p... more This paper reports on several experiments performed by the TanDEM-X constellation that could be potentially implemented as operational modes in future SAR missions. Many of them have been already demonstrated experimentally and could be repeated during a possible next pursuit monostatic phase with TanDEM-X. The new modes include new single-look products as well as interferometric ones, some of which are included in this paper as an example of their potential performance.
TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is an innovative formation flying... more TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurements) is an innovative formation flying radar mission that opens a new era in spaceborne radar remote sensing. The primary objective is the acquisition of a global Digital Elevation Model (DEM) with unprecedented accuracy (12 m horizontal and 2 m vertical resolution). This goal is achieved by extending the TerraSAR-X synthetic aperture radar (SAR) mission by a second, TerraSAR-X like satellite (TDX) flying in close formation with TerraSAR-X (TSX). Both satellites form together a large singlepass SAR interferometer with the opportunity for flexible baseline selection. This enables the acquisition of highly accurate cross-track interferograms without the inherent accuracy limitations imposed by repeat-pass interferometry due to temporal decorrelation and atmospheric disturbances. Besides the primary goal of the mission, several secondary mission objectives based on along-track interferometry as well as new bistatic and multistatic SAR techniques have been defined, representing an important and innovative asset of the TanDEM-X mission. TanDEM-X is implemented in the framework of a public-private partnership between the German Aerospace Center (DLR) and EADS Astrium GmbH. The TanDEM-X mission was successfully launched in June 2010 and started operational data acquisition in December 2010. This paper provides an overview of the TanDEM-X mission and summarizes its actual status and performance. Furthermore, results from several scientific radar experiments are presented that show the great potential of future formation flying interferometric SAR missions to serve novel remote sensing applications.
Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination boa... more Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination board, a spaceborneairborne 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.
ABSTRACT In the paper the usability of LTE data transmission from an aircraft to the ground is in... more ABSTRACT In the paper the usability of LTE data transmission from an aircraft to the ground is investigated. Theoretical analyses and experimental measurements have been carried out by using a commercial low-cost LTE modem and the existing LTE base station infrastructure on ground. In the airborne experiment over wide areas a stable LTE connection was achieved.
Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination boa... more Following an original proposal by the authors to the TerraSAR-X (TSX) scientific coordination board, a spaceborneairborne 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.
Since November 2006, DLR operates F-SAR - a new airborne SAR sensor beside its experimental airbo... more Since November 2006, DLR operates F-SAR - a new airborne SAR sensor beside its experimental airborne SAR sensor E-SAR. F-SAR is a totally new development utilizing most modern hardware. It is presently operated in X-band and has been supplemented recently being fully polarimetric. F-SAR already accomplished several flights and acquired SAR data in different operation modes, amongst others in along-track-interferometric
To meet the challenges of ever increasing road traffic and the associated economic and sociologic... more To meet the challenges of ever increasing road traffic and the associated economic and sociological impacts, new techniques and technologies for better traffic management are needed. The TRAMRAD project (Traffic Monitoring with space-based Radar) aims to profit from research and development in earth observation and advances in radar remote sensing techniques to define a future space-based sensor system for the
IEEE Transactions on Geoscience and Remote Sensing, 2000
We report about the first X-band spaceborneairborne bistatic synthetic aperture radar (SAR) exper... more We report about the first X-band spaceborneairborne bistatic synthetic aperture radar (SAR) experiment, conducted early November 2007, using the German satellite TerraSAR-X as transmitter and the German Aerospace Center's (DLR) new airborne radar system F-SAR as receiver. The importance of the experiment resides in both its pioneering character and its potential to serve as a test bed for the validation of nonstationary bistatic acquisitions, novel calibration and synchronization algorithms, and advanced imaging techniques. Due to the independent operation of the transmitter and receiver, an accurate synchronization procedure was needed during processing to make high-resolution imaging feasible. Precise phase-preserving bistatic focusing can only be achieved if time and phase synchronization exist. The synchronization approach, based on the evaluation of the range histories of several reference targets, was verified through a separate analysis of the range and Doppler contributions. After successful synchronization, nonstationary focusing was performed using a bistatic backprojection algorithm. During the campaign, stand-alone TerraSAR-X monostatic as well as interoperated TerraSAR-X/F-SAR bistatic data sets were recorded. As expected, the bistatic image shows a space-variant behavior in spatial resolution and in signal-to-noise ratio. Due to the selected configuration, the bistatic image outperforms its monostatic counterpart in almost the complete imaged scene. A detailed comparison between monostatic and bistatic images is given, illustrating the complementarity of both measurements in terms of backscatter and Doppler information. The results are of fundamental importance for the development of future nonsynchronized bistatic SAR systems.
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Papers by Stefan V Baumgartner