13,238 research outputs found
Bistatic TerraSAR-X/F-SAR Spaceborne-Airborne SAR Experiment: Description, Data Processing and Results
No full textWe report about the first X-band spaceborne-airborne bistatic SAR experiment,
using the German satellite TerraSAR-X as transmitter and DLR's new airborne
radar system F-SAR as receiver. The data were acquired early November 2007.
The importance of the experiment is not only due to its pioneering character, but
also due to its potential to serve as a test-bed for the validation of
non-stationary bistatic acquisition procedures, novel calibration and
synchronisation algorithms, and advanced imaging techniques, as required
for future non-synchronised bistatic SAR missions.
High-resolution bistatic imaging requires in general a perfect synchronisation of the
radar systems, which in the present case is achieved by evaluating the range
histories of several reference targets. After synchronisation, non-stationary
focussing is performed using a bistatic backprojection approach.
Benefiting from the flexibility of both acquisition systems, stand-alone TerraSAR-X
monostatic as well as interoperated TerraSAR-X/F-SAR bistatic data sets have been
recorded; the simultaneous availability of monostatic and bistatic images will help
to understand their similarities and differences. As expected, the bistatic
image shows a space-variant behaviour in spatial resolution and
signal-to-noise ratio; both outperform their monostatic
counterparts in almost the complete imaged scene.
A detailed comparison between the monostatic and bistatic images is
given, illustrating the complementarity of both measurements in terms of
available backscattered energy and Doppler information
Efficient Time-Domain Image Formation with Precise Topography Accommodation for General Bistatic SAR Configurations
No full textDue to the lack of an appropriate symmetry in the acquisition geometry, generalised bistatic SAR cannot benefit from the two main properties of low-to-moderate resolution monostatic SAR: azimuth-invariance and topography-insensitivity. Precise accommodation of azimuth-variance and topography is a real challenge for efficent algorithms working in the Fourier-domain, but can be quite naturally handled by time-domain approaches. We present an efficient and practical implementation of a generalised bistatic SAR image formation algorithm with an accurate accommodation of these two effects. The algorithm has a common structure with the monostatic fast factorised backprojection (FFBP), and is therefore based on subaperture processing. The images computed over the different subapertures are displayed in an advantageous elliptical coordinate system capable of incorporating the topographic information of the imaged scene in an analogous manner as topography-dependent monostatic SAR algorithms do. Analytical expressions for the Nyquist requirements using this coordinate system are derived. The overall discussion includes practical implementation hints and a realistic computational burden estimation. The algorithm is tested with both simulated and actual bistatic SAR data. The actual data correspond to the spaceborne-airborne experiment between TerraSAR-X and F-SAR performed in 2007
and to the DLR-ONERA airborne experiment carried out in 2003. The presented approach proves its suitability for precise imaging of any given scene acquired by any given bistatic SAR configuration
Efficient Time-Domain Focussing for General Bistatic SAR Configurations: Bistatic Fast Factorised Backprojection
No full textDue to the lack of an appropriate symmetry in the acquisition geometry, generalised bistatic SAR cannot benefit from
the two main properties of low-to-moderate resolution monostatic SAR: azimuth-invariance and topography-insensitivity.
Precise accommodation of azimuth-variance and topography is a real challenge for efficent algorithms working in the
Fourier-domain, but can be quite naturally handled by time-domain approaches. We report about the first efficient and
practical implementation of a generalised bistatic SAR imaging algorithm with an accurate accommodation of these two
effects. The algorithm has a common structure with the monostatic fast factorised backprojection (FFBP), and is therefore
based on subaperture processing. The algorithm is tested with both simulated and actual bistatic SAR data. The actual data
correspond to the spaceborne-airborne experiment between TerraSAR-X and F-SAR performed in 2007. The presented
approach proves its suitability for precise imaging of any given scene acquired by any given bistatic SAR configuration
Towards an Interferometric Autofocus for the Estimation of Ionospheric Signatures in Biomass
No full textThis paper presents the workflow towards an improved estimation and correction of phase errors due to trans-ionospheric
propagation in low-frequency Synthetic Aperture Radar (SAR) images when interferometric stacks are available. The
method consists of estimating the absolute ionospheric phase delays in each of the images with traditional methods
like autofocus. These setimations will later be combined with what is obtained during the correction of the differential
ionosphere in interferometric pairs. By running the algorithms on simulated data, it is shown that it is possible to resolve
faster changing phase errors than with the autofocus alone for a more accurate correctio
The Future of Canadian Climate Policy — with Marc Lee
No full textMarc Lee is a Senior Economist at the Canadian Centre for Policy Alternatives\u27 BC Office. In addition to tracking federal and provincial budgets and economic trends, Marc has published on a range of topics from poverty and inequality to globalization and international trade to public services and regulation. Marc is the Co-Director of the Climate Justice Project, a research partnership with UBC\u27s School of Community and Regional Planning that examines the links between climate change policies and social justice.Resources:Climate Justice Project: www.policyalternatives.ca/projects/cli…tice-projectMarc Lee\u27s Posts on Policy Note: www.policynote.ca/author/marclee/Canadian Centre for Policy Alternatives: www.policyalternatives.ca/Marc\u27s Twitter: twitter.com/MarcLeeCCPA International Panel on Climate Change, 2021 report: www.ipcc.ch/report/ar6/wg1
Climate Justice & Inequality: The Future of Canadian Climate Policy — with Marc Lee
No full textMarc Lee is a Senior Economist at the Canadian Centre for Policy Alternatives\u27 BC Office. In addition to tracking federal and provincial budgets and economic trends, Marc has published on a range of topics from poverty and inequality to globalization and international trade to public services and regulation. Marc is the Co-Director of the Climate Justice Project, a research partnership with UBC\u27s School of Community and Regional Planning that examines the links between climate change policies and social justice.Resources: Climate Justice Project: https://www.policyalternatives.ca/projects/climate-justice-projectMarc Lee\u27s Posts on Policy Note: https://www.policynote.ca/author/marclee/Canadian Centre for Policy Alternatives: https://www.policyalternatives.ca/Marc\u27s Twitter: https://twitter.com/MarcLeeCCPA International Panel on Climate Change, 2021 report: https://www.ipcc.ch/report/ar6/wg1
Analysis of Methods for Reconstructing Periodically Missed SAR Data Acquired Close to Nyquist
No full textThe cooperative nature of the TanDEM-X mission bistatic
operation allows the periodically exchange of information between
transmitter and receiver over the SAR acquisition. With the
information gathered during the synchronization (sync) events it is
possible to perform the phase and time referencing necessary for
the calibration of the bistatic SAR image. However, given that
transmitter and receiver are dedicated to the link during the sync
events, the reception of SAR signal is periodically interrupted
leading to gaps in the SAR raw data. Consequently, the processed
SAR image will be corrupted, especially when acquiring close to
the Nyquist rate. The paper addresses different approaches based
on parametric and non-parametric spectral estimation to
reconstruct the missing data and presents results with SAR data
from TerraSAR-X and TanDEM-X
General Processing Approach for Bistatic SAR Systems: Description and Performance Analysis
No full textFor its intrinsic properties, bistatic SAR processing cannot be approached in the same manner monostatic SAR process-
ing is approached. In general, a bistatic SAR processor is more than a powerful focussing algorithm. Because of the
lack of precise time (range) and phase (Doppler) references in non-cooperative (and even cooperative) bistatic systems, a
prior software synchronisation step is used to correct the residual errors caused by the use of different clocks. Moreover,
depending on the bistatic configuration, different kinds of SAR focussing algorithms can be used. Azimuth-invariant
configurations may benefit from the convolution property of the Fourier transform, whereas more general configurations
are better suited for efficient time-domain techniques. A discussion on the performance of three Fourier-domain focussing
algorithms, range-Doppler, chirp scaling, and range migration, is included in the paper
Space-based Bistatic Radar for UAV Autonomous Navigation and Surveillance System
No full textBistatic radars offer several advantages when compared to their monostatic counterparts. In addition to increased performance,
sensitivity, coverage and revisit times, all of them parameters which are mainly dependent on their spatial configuration, bistatic
radars offer the objective advantage of being more robust to jamming, since the receiver operates as a mere passive system.
The proposed system consists of a spaceborne-based radar transmitter illuminating an area of interest and one or several radar
receivers mounted on a UAV to perform a two-goal mission: a) help autonomous navigation of the UAV by performing the sense
& avoid function, and b) perform surveillance of the overflown area using high-resolution remote sensing techniques. Although the
requirements for these significantly different tasks might seem distant, having a spaceborne transmitter ensures that the coverage
needed for both purposes is achievable. Assuming the technical feasibility of the complete system, it would provide a cheap and
robust manner for enabling global UAV flight, while enabling continuous all-weather imaging capabilities of the UAV-overflown
areas with fair resolution values
New processing approach and results for bistatic TerraSAR-X/F-SAR spaceborne-airborne experiments
No full textFollowing the success of the first bistatic
spaceborne-airborne experiment between TerraSAR-X and FSAR
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 spaceborneairborne
images are also presented in this paper
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