Björn J. Döring

Björn J. Döring
German Aerospace Center (DLR) | DLR · Microwaves and Radar Institute

Dr.-Ing.

About

115
Publications
12,227
Reads
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704
Citations
Additional affiliations
January 2006 - present
German Aerospace Center (DLR)
January 2006 - May 2016
German Aerospace Center (DLR)
Position
  • Research associate and calibration engineer

Publications

Publications (115)
Thesis
Full-text available
Synthetic aperture radar (SAR) systems allow to quantitatively measure the radar backscatter of an imaged terrain region. In order to achieve comparability between measurement results, traceable radiometric calibration is indispensable. The central claim of the work is that nowadays, however, radiometric SAR measurements are not traceably calibrate...
Article
Full-text available
Recently equivalent radar cross section (ERCS) was introduced as a new radiometric measurement quantity for synthetic aperture radar (SAR) systems. The focus of this paper is the dependence of a point target's ERCS (which is proportional to the pixel intensity) on the passband of the measuring SAR system. The SAR passband is mostly defined by the r...
Article
Full-text available
Stringent radiometric SAR system requirements often significantly shape the design and cost of modern SAR systems. Yet the wording in current requirement documents is ambiguous, and a diligent conformance assessment at the end of project phases currently questionable. In order to improve the situation for future SAR missions, a review of the requir...
Article
Full-text available
A Synthetic Aperture Radar (SAR) system measures among other quantities the terrain radar reflectivity. After image calibration, the pixel intensities are commonly expressed in terms of radar cross sections (for point targets) or as backscatter coefficients (for distributed targets), which are directly related. This paper argues that pixel intensit...
Article
Full-text available
The backscattering from man-made point targets like passive corner reflectors and active transponders is often used as a radiometric calibration standard for synthetic aperture radar (SAR) calibration. As new systems emerge and the demand for more accurate systems increases, it becomes necessary to better understand the effects of real or imperfect...
Article
A necessary activity for any SAR system is its calibration to establish the relation between radar measurements and geophysical parameters. During this process, all essential parameters of a SAR image are linked to their geophysical quantities. This includes the geolocation of the SAR image, its backscattering characteristics (in amplitude and in p...
Conference Paper
Full-text available
The radiometric calibration of synthetic aperture radar (SAR) systems is typically based on the known backscatter of calibration point targets such as transponders. Before a SAR calibration campaign can begin it is therefore necessary to determine the backscatter (radar cross section or RCS) of the transponder itself. Known methods suffer from unne...
Conference Paper
Polarimetric synthetic aperture radar (SAR) systems require verification and calibration of their polarimetric performance after launch. Dual-antenna calibration transponders with freely rotatable, linearly-polarized antennas are one of the most common calibration targets for this task. Because the transponders are used as a measurement standard, a...
Conference Paper
Full-text available
For the radiometric calibration of spaceborne synthetic aperture radar systems, active targets with known backscatter, so called transponders, are used. These serve as an external absolute reference, and the quality of the derived calibration parameters depends on the quality of the deployed transponders. Due to the temperature dependent behavior o...
Article
In the frame of the GMES program, the main objective of the Sentinel-1 mission is to ensure the continuity of SAR data ac- quisitions in C-band for global earth monitoring. Sentinel-1A is the first of two C-band satellites launched in April 2014. In addition to the commissioning of Sentienl-1A executed by ESA, an independent verification of the sys...
Conference Paper
For recent and upcoming spaceborne SAR missions based on compact or full polarimetric operation modes, the calibration of these SAR systems becomes more and more complex. In order to reduce the number of reference targets used during the calibration phase it is essential to use polarimetric active radar calibrators – PARC offer-ing a flexible scatt...
Conference Paper
Full-text available
Transponders are, besides trihedral corner reflectors, the most commonly used measurement standards in radiometric SAR calibration. They allow signal recording for the reconstruction of the azimuth pattern of the SAR system, adjustments of the backscattering matrix for polarimetric applications, and radar cross sections (RCSs) which are potentially...
Conference Paper
Full-text available
The goal of radiometric calibration in synthetic aperture radar (SAR) is to achieve comparability between measurement results acquired with different systems (e.g. RADARSAT-2 and Sentinel-1), at different times (e.g. image stacks over many years), or with different system settings (e.g. center frequency or polarization). At the beginning of the cal...
Conference Paper
Full-text available
Transponders are, besides trihedral corner reflectors, the most commonly used measurement standards in radiometric SAR calibration. They allow signal recording for the reconstruction of the azimuth pattern of the SAR system, adjustments of the backscattering matrix for polarimetric applications, and radar cross sections (RCSs) which are potentially...
Conference Paper
A SAR system has to be calibrated for quantitative measurement. During this process all essential parameters of a SAR image are linked to their geophysical quantity. This includes the location of the image pixel, its backscattering characteristics (in amplitude and in phase) and polarimetric information. The Microwave and Radar Institute of the DLR...
Conference Paper
Full-text available
The technological advancement of upcoming synthetic aperture radar (SAR) satellite missions leads to innovative challenges for the calibration as well. In order to provide an active reference target for an accurate absolute radiometric calibration the knowledge of the backscattering characteristics is essential. For the recently developed DLR C-ban...
Article
Full-text available
Transponders (also known as polarimetric active radar calibrators or PARCs) are commonly used for radiometric calibration of synthetic aperture radars (SARs). Currently three methods for the determination of a transponder's frequency-dependent radar cross section (RCS) are used in practice. These require either to measure disassembled transponder c...
Conference Paper
Full-text available
In the frame of the GMES program of European Space Agency (ESA), the Sentinel-1A satellite was launched in April 2014 to ensure the continuity of SAR data acquisitions in C-band for global earth monitoring. The calibration of the SAR instrument was performed by ESA and their partners during the commissioning phase. In order to execute an independen...
Conference Paper
Full-text available
Spaceborne synthetic aperture radars (SAR) are systems capable of acquiring high-resolution earth-observation data independent on time of day and weather. These SAR systems have to be calibrated before first use and at regular intervals. For these radiometric calibrations active targets with known backscatter, so called transponders, serve as an ex...
Article
Full-text available
The progressive development of upcoming satellite missions using synthetic aperture radar (SAR) lead to novel challenges also for the reference targets. In order to provide a reference target for an accurate absolute radiometric calibration the knowledge of the backscattering characteristics is essential. Whereas usually one single measurement is u...
Conference Paper
Full-text available
Upcoming spaceborne synthetic aperture radar (SAR) missions like the Sentinel-1 mission pushing the limits toward better image quality especially in radiometric accuracy. Highly accurate calibration of the instrument is one of the key factors on this way. Therefore the DLR has developed a novel, very stable, and exactly characterized transponder ca...
Conference Paper
Stringent radiometric SAR system requirements often significantly shape the design and cost of modern SAR systems. Yet the wording in current requirement documents is ambiguous, and a diligent conformance assessment at the end of project phases currently questionable. In order to improve the situation for future SAR missions, a review of the requir...
Conference Paper
Full-text available
The progressive development of upcoming satellite missions using synthetic aperture radar (SAR) lead to novel challenges also for the reference targets. In order to provide a reference target for an accurate absolute radiometric calibration the knowledge of the backscattering characteristics is essential. Whereas usually one single measurement is u...
Article
Full-text available
A synthetic aperture radar (SAR) system requires external absolute calibration so that radiometric measurements can be exploited in numerous scientific and commercial applications. Besides estimating a calibration factor, metrological standards also demand the derivation of a respective calibration uncertainty. This uncertainty is currently not sys...
Conference Paper
In the frame of the GMES program, the main objective of the Sentinel-1 mission is to ensure the continuity of SAR data ac- quisitions in C-band for global earth monitoring. Sentinel-1A is the first of two C-band satellites launched in April 2014. In addition to the commissioning of Sentienl-1A executed by ESA, an independent verification of the sys...
Conference Paper
Since the conception of synthetic aperture radar (SAR) systems in 1953, radar cross section (RCS) has been used as the measurement quantity for reporting the backscatter of point targets in SAR images. Consequently, radiometric calibration targets like corner reflectors or transponders have also been characterized by their RCS. This presentation wi...
Conference Paper
This presentation summarizes DLR's development efforts toward next generation SAR calibration targets: 2.8 m corner reflectors and C-band transponders.
Article
This document aims to derive the absolute radiometric accuracy for the Sentinel 1 SAR satellite. It integrates results found by EADS Astrium regarding the SAR instrument and processing, and derives additional uncertainty contributions with respect to the external calibration and the atmosphere.
Article
Full-text available
The antenna model used for correcting the influence of the antenna pattern on synthetic aperture radar (SAR) images requires on-ground validation and in-flight verification. A methodology for the in-flight verification that is based upon the measurement of azimuth antenna patterns using ground receivers has been successfully demonstrated for the op...
Article
The antenna model used for correcting the influence of the antenna pattern on synthetic aperture radar (SAR) images requires on-ground validation and in-flight verification. A methodology based on the in-flight measurement of azimuth patterns with ground receivers has been successfully performed for the missions TerraSAR-X (TSX) and TanDEM-X (TDX),...
Article
This report summarizes the RADARSAT-2/Kalibri Transponder campaign and analysis results.
Article
Technical Note on the absolute radiometric bias budget update for the CoReH2O mission, phase A system study extension.
Article
The ESA Sentinels constitute the first series of operational satellites responding to the Earth Observation needs of the EU-ESA Global Monitoring for Environment and Security (GMES) programme. The GMES space component relies on existing and planned space assets as well as on new complementary developments by ESA. In contrast to SAR systems already...
Article
Technical Note on the absolute radiometric bias budget update for the CoReH2O mission, phase A system study extension.
Article
Radar cross section has long been the measurement quantity of choice to describe the radar reflectivity of point targets in calibrated synthetic aperture radar (SAR) images. Derived quantities like the backscatter coefficient are equally in wide-spread use to radiometrically describe, in scientific applications often even more relevant, distributed...
Conference Paper
Radar cross section has long been the measurement quantity of choice to describe the radar reflectivity of point targets in calibrated synthetic aperture radar (SAR) images. Derived quantities like the backscatter coefficient are equally in wide-spread use to radiometrically describe, in scientific applications often even more relevant, distributed...
Article
The requirements on new spaceborne synthetic aperture radar (SAR) missions are always pushed towards better image quality with respect to signal-to-noise ratio, radiometric accuracy, and spatial resolution. An accurate radiometric calibration of the whole SAR system is crucial to cope with the demand on high image quality. Among other factors, the...
Conference Paper
The requirements on new spaceborne synthetic aperture radar (SAR) missions are always pushed towards better image quality with respect to signal-to-noise ratio, radiometric accuracy, and spatial resolution. An accurate radiometric calibration of the whole SAR system is crucial to cope with the demand on high image quality. Among other factors, the...
Conference Paper
Full-text available
Reference point targets like active transponders or passive corner reflectors provide a reference reflectivity against which the instrument offset can be determined. Up to now, no direct link between the reference point target properties (like its frequency response) and its perceived backscattering was available. In this paper it is proposed to cl...
Conference Paper
Full-text available
Transponders for synthetic aperture radar (SAR) need to be extremely precise in order to qualify as absolute calibration references for the increasingly demanding new SAR systems. To guarantee highest accuracy and stability even components which normally are considered ideal, have to be be taken into account. This paper shows the environmental infl...
Conference Paper
The requirements on new spaceborne synthetic aperture radar (SAR) missions are always pushed towards better image quality with respect to signal-to-noise ratio, radiometric accuracy, and spatial resolution. Therefore an accurate calibration of the SAR system and the final product is essential. The quality of the calibration depends on the utilized...
Conference Paper
Full-text available
The primary object of the TanDEM-X mission is to generate a highly accurate digital elevation model (DEM) with never achieved accuracy on global scale [1]. But in addition to this DEM acquisition realized by a helix constellation of two satellites, nominal TerraSAR-X operation shall be available anymore, i.e. the bistatic TanDEM-X mission and the m...
Conference Paper
In addition to the first satellite TSX already in-flight since 2007 [1], the second satellite TDX of the TanDEM-X system could be successfully launched in 2010 [2]. The primary object of the TanDEM-X mission is to generate a highly accurate digital elevation model (DEM) with never achieved accuracy on global scale. But in addition to this DEM acqui...
Conference Paper
A synthetic aperture radar (SAR) system measures the radar reflectivity of the earth's surface for a multitude of scientific and commercial applications. In many cases, accurate absolutely calibrated images are required by end-users. The backscattering from man-made point targets like passive corner reflectors and active transponders is often used...
Conference Paper
In recent years, the antenna technology for spaceborne synthetic aperture radar (SAR) systems has developed from passive slotted waveguide arrays (e.g. ERS-1/2 or X-SAR) to active phased arrays (e.g. ASAR/ENVISAT or TerraSAR-X), offering electronic beam steering capabilities required for acquisitions in different swath geometries and for operation...
Conference Paper
Full-text available
In example of measurements performed in space with TerraSAR-X, an approach for an accurate antenna characterization is described. TerraSAR-X was launched in June 2007 and is a highly flexible X-band radar satellite based on an active phased array antenna. Its primary objective is the acquisition of high quality SAR images in a multitude of possible...
Conference Paper
Full-text available
The primary object of the TanDEM-X mission is to generate a highly accurate digital elevation model (DEM) with never achieved accuracy on global scale. But in addition to this bistatic TanDEM-X mission the monostatic TerraSAR-X mission have to be operated in parallel with both satellites. Consequently the second satellite TDX, successfully launched...
Conference Paper
In 2009, two years after launch of TerraSAR-X, dedicated extensive calibration campaigns were performed for both the recalibration of the whole TerraSAR-X system and for the experimental Dual Receive Antenna (DRA) mode. The effective and exact calibration techniques already successfully applied for commissioning TerraSAR-X in 2007 have been shown o...