A. Gustavsson

Blekinge Institute of Technology , Karlskrona, Blekinge, Sweden

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Publications (68)21.93 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, the results of moving-target detection in multichannel UHF-band synthetic aperture radar (SAR) data are shown. The clutter suppression is done using finite-impulse response (FIR) filtering of multichannel SAR in combination with a two-stage fast-backprojection algorithm to focus the moving target using relative speed. The FIR filter coefficients are chosen with the use of space-time adaptive processing filtering. Two parameters are used for target focusing, target speed in range and in azimuth. When the target is focused, both speed parameters of the target are found. In the experimental results, two channels were used in order to suppress clutter. In the resulting SAR images, it is obvious that very strong scatterers and the forest areas have been suppressed in comparison to the moving target in the image scene. The gain obtained can be measured using signal-to-clutter-and-noise-ratio gain, which is about 19 dB. Another way to measure the signal processing gain is the ability to suppress the strongest reflecting object in the SAR scene. The gain of the target in relation to this object is 25 dB. This shows that using UHF-band SAR ground moving target indication (GMTI) for suppressing forest and increasing the target signal can work.
    IEEE Transactions on Geoscience and Remote Sensing 01/2014; 52(7):4005-4013. · 3.47 Impact Factor
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    ABSTRACT: In this paper one way to combine UHF Synthetic Aperture Radar (SAR) processing with MIMO radar is shown. The SAR processing is conducted in the time domain using a fast back projection algorithm (FBP). Each channel is SAR processed separately until a middle stage. Some results have been obtained using 2-channel data from the LORA system. The experimental results show that it is possible to estimate target speed parameters as well as it is possible to suppress forest clutter significantly in the SAR images. For the specific dataset used, the SAR data collection time is 4.6s and the target is a truck with a corner reflector mounted on the back. The results show a good ability to suppress the forest clutter while not suppressing the target signal. Also, in order to obtain the correct target speed components in azimuth and range for focusing, the target dynamic parameters in target focusing and in the steering vector were regulated.
    Synthetic Aperture Radar (APSAR), 2013 Asia-Pacific Conference on; 01/2013
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    ABSTRACT: In this paper, a method for moving target relative speed estimation and refocusing based on synthetic aperture radar (SAR) images is derived and tested in simulation and on real data with good results. Furthermore, an approach on how to combine the estimation method with the refocusing method is introduced. The estimation is based on a chirp estimator that operates in the SAR image and the refocusing of the moving target is performed locally using subimages. Focusing of the moving target is achieved in the frequency domain by phase compensation, and therefore makes it even possible to handle large range cell migration in the SAR subimages. The proposed approach is tested in a simulation and also on real ultrawideband (UWB) SAR data with very good results. The estimation method works especially well in connection with low frequency (LF) UWB SAR, where the clutter is well focused and the phase of the smeared moving target signal becomes less distorted. The main limitation of the approach is target accelerations where the distortion increases with the integration time.
    IEEE Transactions on Aerospace and Electronic Systems 01/2012; 48(3):2426-2436. · 1.30 Impact Factor
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    ABSTRACT: We present results from a bistatic SAR experiment conducted with two airborne radars operating in the band 222–460 MHz using HH-polarization. The systems used a step-frequency chirp waveform and were synchronized using GPS 1PPS signals. The processed and analysed data were collected during four flight missions over a test site including forested terrain and a controlled vehicle deployment. Results indicate that forest clutter decreases and target-to-clutter ratio increases in bistatic SAR with bistatic separation in elevation compared to monostatic SAR.
    Radar Systems (Radar 2012), IET International Conference on; 01/2012
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    ABSTRACT: Circular-aperture synthetic aperture radar (SAR) imaging has been evaluated using the airborne very high frequency (VHF) band Coherent All RAdio BAnd Sensing (CARABAS)-II system (20–90 MHz). Images, as well as results, from detection of vehicles in dense forest concealment have been compared with linear-aperture SAR. Circular-aperture SAR imaging provides higher image resolution and increased object information, but complexity of signal processing and requirements on imaging geometry accuracy increases. The latter is, however, partly mitigated by using low frequencies in the VHF band. A high-quality digital elevation model is used to ensure high-quality image focusing and to avoid distorting object shape. Contrast optimization is used to reduce global focusing errors. The image resolution is observed to be about 1 $\hbox{m}^{2}$ in agreement with theoretical predictions. Detection performance has been evaluated using image data from a full circular synthetic aperture, i.e., 360$^{\circ}$ of aspect angle variation. Results, both for single-pass detection (SPD) and change detection (CD), show a considerable advantage compared with detection based on linear-aperture SAR. The detection probability for SPD increases from 0.4 to 0.8 at a false-alarm rate (FAR) of $30/\hbox{km}^{2}$. For CD, the detection probability increases from 0.7 to 0.9 at a FAR of $2/\hbox{km}^{2}$ .
    IEEE Transactions on Geoscience and Remote Sensing 01/2012; 50(4):1329-1339. · 3.47 Impact Factor
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    ABSTRACT: We present results from the LORAMbis bistatic VHF/UHF-band SAR experiment conducted in September 2010. The SAR flights were performed with the French SETHI system and the Swedish LORA system installed in two aircraft. Frequency band was 222-460 MHz and polarization was HH. Results from two tests sites (Kvarn and Remningstorp, both in southern Sweden) show that forest clutter generally decreases for increasing bistatic elevation angles. This observation is explained by reduction of the ground-trunk double-bounce scattering mechanism. Results also indicate that vehicles in forest concealment are often better discriminated in bistatic compared to monostatic SAR images. Examples of signal-to-clutter-ratio measurements for vehicles show an increase 7-17 dB when the bistatic elevation angles increased from 0° (quasi-monostatic) up to 10°. These show the potential for improved target detection using VHF/UHF-band bistatic SAR.
    Geoscience and Remote Sensing Symposium (IGARSS), 2012 IEEE International; 01/2012
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    ABSTRACT: Low frequency synthetic-aperture radar (SAR) in combination with change detection techniques can be used to search for stationary ground targets. In particular, the method has shown a great potential when vehicle-size objects are obscured by foliage. However. one possibility is to improve the detection capabilities to increase the aperture angle of the radar data acquisition to make sure that the strong cardinal responses of a typical vehicle are registered. This implies an angle of at least 180° to include the strongest (broadside) response when the target orientations are unknown. HF-VHF SAR data (20-90 MHz) have earlier successfully been exploited on this and now tests have also been conducted with the airborne VHF-UHF SAR system LORA (220-430 MHz) using the maximum angle 360°, i.e. a full circle. A first look on this data set indicates a possibility to obtain an extended response signature from the hidden targets compared to the corresponding images generated from the linear tracks made during the same flight mission. The image processing of circular tracks becomes more complex and precise processing of the imaging geometry is necessary, i.e. both accurate navigation data as well as a dense digital elevation model (DEM) of the illuminated ground segment.
    Geoscience and Remote Sensing Symposium (IGARSS), 2012 IEEE International; 01/2012
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    ABSTRACT: Airborne bistatic SAR data have been collected at VHF- and UHF-band to investigate clutter suppression in forested and urban areas. The synchronization between the SAR systems is accomplished using the 1-PPS signal provided by the GPS system. The same signal is also used as input to a disciplined 10 MHz master oscillator integrated in both radar systems to maintain sufficient phase stability. Images have successfully been generated using the time domain fast factorized backprojection algorithm, modified for the bistatic case. Clutter suppression has been observed when comparing the monostatic and bistatic images acquired simultaneously by the two SAR sensors. Work is in progress to quantify and compare the obtained results.
    Geoscience and Remote Sensing Symposium (IGARSS), 2012 IEEE International; 01/2012
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    ABSTRACT: The ESA funded campaign BioSAR 2010 was carried out at the forestry test site Remningstorp in southern Sweden, in support to the BIOMASS satellite mission under study. Fully polarimetric SAR data were successfully acquired at Land P-band using ONERA's multi-frequency system SETHI. In addition with other data types gathered, e.g. LiDAR and in-situ measurements, the compiled data set will be used for analyses and comparisons with biomass estimation results obtained at the same test site in the campaign BioSAR 2007, in which DLR's E-SAR made the SAR imaging. Detection of forest changes, robustness of biomass retrieval algorithms and long-term P-band coherence will be in focus as well as cross-validations between the two SAR sensors.
    Geoscience and Remote Sensing Symposium (IGARSS), 2011 IEEE International; 08/2011
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    ABSTRACT: The paper presents results from a bistatic SAR experiment conducted using two airborne SAR systems operating in the high VHF- and low UHF-band. The Swedish SAR system LORA operated together with the French SAR system SETHI and collected data in different bistatic geometries in the frequency band 222-460 MHz and using HH-polarization. The two SAR systems were synchronized using the 1PPS GPS-signal. Data were collected during four flight missions over the main test site with forested terrain and buildings as well as controlled target deployments. A fifth mission was included over a second test site with an extensive data base of forest parameters but without target deployments. The bistatic radar data have been processed to SAR images and first analysis completed. Results show significant suppression of strong forest clutter and that the effect increases with bistatic elevation angle. The clutter reduction is observed in areas with dominating double-bounce scattering. Data analysis shows that forest clutter can be suppressed by 10 dB for a bistatic elevation angle of 10°.
    Proc SPIE 05/2011;
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    ABSTRACT: The ESA funded campaign BioSAR 2010 was carried out at the forestry test site Remningstorp in southern Sweden, in support to the BIOMASS satellite mission under study. Fully polarimetric SAR data were successfully acquired at L- and P-band using ONERA’s multi-frequency system SETHI. In addition with other data types gathered, e.g. LiDAR and in-situ measurements, the compiled data set will be used for analyses and comparisons with biomass estimation results obtained at the same test site in the campaign BioSAR 2007, in which DLR’s E-SAR made the SAR imaging. Detection of forest changes, robustness of biomass retrieval algorithms and long-term P-band coherence will be in focus as well as cross-validations between the two SAR sensors.
    2011 IEEE International Geoscience and Remote Sensing Symposium, IGARSS 2011, Vancouver, BC, Canada, July 24-29, 2011; 01/2011
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    ABSTRACT: Moving-target detection in ultrawideband (UWB) synthetic aperture radar (SAR) is associated with long integration time and must accommodate azimuth focusing for reliable detection. This paper presents the theory on detection of moving targets by focusing and experimental results on single-channel SAR data aimed at evaluating the detection performance. The results with respect to both simulated and real data show that the ability to detect moving targets increases significantly when applying the proposed detection technique. The improvement in signal-to-clutter noise ratio, which is a basic requisite for evaluating the performance, reaches approximately 20 dB, using only single-channel SAR data. This gain will be preserved for the case of multichannel SAR data. The reference system for this study is the airborne UWB low-frequency SAR Coherent All RAdio BAnd Sensing II.
    IEEE Transactions on Geoscience and Remote Sensing 11/2010; · 3.47 Impact Factor
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    ABSTRACT: In this letter, we propose an approach to suppress radio-frequency interference (RFI) in ultrawideband (UWB) low-frequency synthetic aperture radar (SAR). According to the proposal, RFI is suppressed by using an adaptive line enhancer controlled by the normalized least mean square algorithm. The approach is tested successfully on real UWB low-frequency SAR data. In order to keep the computational burden down, possible ways to integrate the RFI suppression approach into SAR imaging algorithms are also suggested.
    IEEE Geoscience and Remote Sensing Letters 11/2010; · 1.82 Impact Factor
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    ABSTRACT: Time-domain back-projection is able to generate focused synthetic-aperture radar images for the most general geometries but at the expense of high computational burden. With the advent of the fast factorized back-projection algorithm, however, it is now possible to achieve computational performance in parity with frequency-domain algorithms and without the restrictions on data symmetry of the latter. In the paper, we show that the fast factorized back-projection algorithm can also be extended to bistatic SAR data with retained computational performance. Image results are presented based on bistatic VHF/UHF-band registrations acquired with the two airborne SAR sensors LORA and SETHI.
    Synthetic Aperture Radar (EUSAR), 2010 8th European Conference on; 07/2010
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    ABSTRACT: Multiple scattering is often a dominating scattering mechanism in VHF-band SAR, in particular in scenes including forested and urban terrain. Most important in this context is multiple scattering generated by double- or triple-bounce scattering from structures with orthogonal corners which often dominate for monostatic SAR geometries. Examples include double-bounce scattering from vertical tree stems or building walls on horizontal ground. In such situations, bistatic SAR may offer a significant advantage compared to monostatic SAR by choosing a suitable bistatic imaging geometry. We give experimental results which show increased signal-to-clutter ratio in bistatic VHF-based SAR (28-73 MHz). Results show that the signal-to-clutter ratio of a vehicle truck in a background of forest and urban clutter increases by up to 10 dB when the broadside bistatic elevation angle increases from 4 to 20°. The results indicate that significant improvement in detection performance can be expected for vehicle-sized objects in forest and urban terrain by using bistatic geometries in VHF-band SAR.
    IET Radar Sonar ? Navigation 07/2010; · 0.92 Impact Factor
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    ABSTRACT: LORAMbis is the experimental part of a joint research program between Sweden and France. The objective is to evaluate the performance of low frequency bistatic SAR for clutter suppression in various applications, e.g. under-foliage target detection or mapping of urban scenes. The airborne bistatic SAR data are acquired using the VHF/UHF component of the ONERA SAR system SETHI and the VHF/UHF LORA system operated by FOI. The first data collection campaign was conducted in December 2009. Focused bistatic SAR images have been formed and indicate that the implemented synchronization method is sufficient. It is based on a GPS disciplined 10 MHz reference signal that is generated in both systems.
    Radar Conference, 2010 IEEE; 06/2010
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    ABSTRACT: We describe an extensive data collection and analysis of change detection using VHF- and UHF-band SAR data. Two airborne systems (CARABAS-II: 22-82 MHz, LORA: 225-470 MHz) acquired data for multiple headings and incidence angles. Twenty one targets of five types were deployed in forest concealment. CARABAS-II gives the best performance for the target types investigated. Analysis of the data shows that performance degrades for increasing incidence angle, mainly due to reduced target radar-cross section. It is also shown that different change detectors give different performance. The best detector for one incidence angle is not necessarily best for another incidence angle.
    Radar Conference, 2010 IEEE; 06/2010
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    ABSTRACT: Radar imaging of tropical vegetation at VHF- and UHF-band has been performed using the airborne SAR sensors CARABAS-II and LORA, respectively. The acquired data set is limited to HH-polarized registrations only. The area mapped exhibits a rough terrain with dramatic topographic variations, mostly covered by dense tropical rain forests. Multiple illumination directions spanning 360° were adopted in the data collection for both sensors to overcome the shadowing due to the high relief topography. For each heading, the SAR images generated, adjacent in azimuth and from all imaging passes, were calibrated and geocoded separately and then merged into a mosaic representing the full ground coverage. A first output from the forest backscatter analysis indicates a 12 dB lower level at VHF-band at an incidence angle of about 70°. However, this preliminary result is based on one sample point only, where the investigated forested area was located on a fairly flat ground surface.
    IEEE International Geoscience & Remote Sensing Symposium, IGARSS 2010, July 25-30, 2010, Honolulu, Hawaii, USA, Proceedings; 01/2010
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    ABSTRACT: This document describes the radar data acquired during the BIOSAR campaign carried out in October 2008 in Northern Sweden. The main objective of the BIOSAR campaign is summarised and a description of the flight campaign and the acquired airborne and ground data are given. In the frame of its Earth Observation Envelope Programme of the European Space Agency (ESA), BIOSAR supports geophysical algorithm development, their calibration and validation as well as the simulation of future space-borne Earth Observation missions. The next generation of ESA Earth Observation satellites include a series of innovative satellites dedicated to a specific application. BIOSAR supports the current selected candidate Earth Explorer Mission BIOMASS. The main objective of BIOMASS is the estimation of forest biomass in order to support carbon modelling using longer wavelength. The BIOSAR 2008 campaign collects in-situ and airborne SAR in support of decisions being taken on satellite instrument configurations for the BIOMASS satellite mission. In addition it provides an important database for the study of longer term mission concepts. While the BIOSAR 2007 campaign collected data with the objective to investigate the effect of temporal decorrelation at P-band with 100MHz and 6MHz bandwidth in southern Sweden, BIOSAR 2008 recorded data at boreal forests with strong topographic effects in northern Sweden to investigate the effect on forest height estimation and radar backscatter signal variation.
    11/2009;
  • [Show abstract] [Hide abstract]
    ABSTRACT: This document describes the radar data acquired during the BIOSAR campaign carried out in October 2008 in Northern Sweden. The main objective of the BIOSAR campaign is summarised and a description of the flight campaign and the acquired airborne and ground data are given. In the frame of its Earth Observation Envelope Programme of the European Space Agency (ESA), BIOSAR supports geophysical algorithm development, their calibration and validation as well as the simulation of future space-borne Earth Observation missions. The next generation of ESA Earth Observation satellites include a series of innovative satellites dedicated to a specific application. BIOSAR supports the current selected candidate Earth Explorer Mission BIOMASS. The main objective of BIOMASS is the estimation of forest biomass in order to support carbon modelling using longer wavelength. The BIOSAR 2008 campaign collects in-situ and airborne SAR in support of decisions being taken on satellite instrument configurations for the BIOMASS satellite mission. In addition it provides an important database for the study of longer term mission concepts. While the BIOSAR 2007 campaign collected data with the objective to investigate the effect of temporal decorrelation at P-band with 100MHz and 6MHz bandwidth in southern Sweden, BIOSAR 2008 recorded data at boreal forests with strong topographic effects in northern Sweden to investigate the effect on forest height estimation and radar backscatter signal variation.
    06/2009;

Publication Stats

210 Citations
21.93 Total Impact Points

Institutions

  • 2007–2010
    • Blekinge Institute of Technology
      • Department of Electrical Engineering (AET)
      Karlskrona, Blekinge, Sweden
    • Umeå University
      Umeå, Västerbotten, Sweden
  • 1999–2010
    • Swedish Defence Research Agency
      Tukholma, Stockholm, Sweden