Space-surface Bistatic Synthetic Aperture Radar Research Articles

Space-Surface Bistatic SAR Image Enhancement Based on Repeat-Pass Coherent Fusion With Beidou-2/Compass-2 as Illuminators

Low signal power density limits the performance of space-surface bistatic synthetic aperture radar (SS-BiSAR) using Global Navigation Satellite System (GNSS) satellites as illuminators. To tackle this problem, in this letter, a novel bistatic SAR image enhancement technique based on repeat-pass coherent fusion is proposed. The works in this letter include three aspects. First, repeat-pass experiments are designed to ensure the best resolution. Second, a modified CLEAN technique is applied to remove the direct signal interference from the focused BiSAR images. Third, a coherence-processing method is proposed to implement coherence of each repeat-pass BiSAR image and then they are coherently fused to obtain a quality-improved BiSAR image. Twenty-two days of repeat-pass BiSAR experiments with Beidou-2/Compass-2 inclined geosynchronous orbit satellites as illuminators have been designed and conducted. The data were processed by the proposed method. The results show that the method can obtain better image quality compared with the traditional noncoherent fusion method and the single-day imaging result, which validates the proposed method and proves the huge potential in realizing local area monitoring with SS-BiSAR using GNSS satellites as illuminators.

Basic performance of space-surface bistatic SAR using BeiDou satellites as transmitters of opportunity

The basic performance of space-surface bistatic synthetic aperture radar (SS-BSAR) using BeiDou satellites as transmitters of opportunity is presented. The transmitted signal, the satellite trajectory, and the observation time are analyzed to demonstrate the potential of BeiDou satellites to be used as transmitters of SS-BSAR. When a BeiDou medium earth orbit (MEO) satellite is used, the signal-to-noise ratio and the resolution are examined for different SS-BSAR cases, where the receiver is fixed on the ground or mounted on a moving platform. Since the parameters of the BeiDou geostationary earth orbit (GEO) satellite and the inclined geosynchronous satellite orbit (IGSO) satellite are different from those of the MEO satellite, the peculiarities of SS-BSAR with the GEO or IGSO satellite as transmitter are analyzed and then compared with the case of MEO satellite. In order to show the performance difference of SS-BSAR with BeiDou satellites as transmitters, comparisons with other global navigation satellite system (GNSS) transmitters are also made. The theoretical results show that SS-BSAR using BeiDou satellites as transmitters can achieve different sounding performance and can provide some new potential applications compared to other GNSS transmitters.

Space-surface bistatic synthetic aperture radar with navigation satellite transmissions: a review

This paper reviews the theory and practice of Space-Surface Bistatic Synthetic Aperture Radar (SS-BSAR) using navigation satellites as transmitters. In recent years, this innovative technology has reached a maturity stage which allows it to be considered for a wide range of applications. The paper covers the fundamental aspects of this technology as a radar system, such as the resolution, power budget and Point Spread Function (PSF) analysis, as well as its signal processing aspects and the state of the art in terms of advanced SAR techniques that it enables. Finally, the theoretical aspects of the paper may be directly transferred to the more generic SS-BSAR concept.

Generic signal synchronisation algorithm for passive global navigation satellite system‐based synthetic aperture radar

This study presents the methods and results of a new signal synchronisation algorithm for passive imaging by means of space–surface bistatic synthetic aperture radar with global navigation satellite system transmitters. The operating principles of the algorithm are described analytically. The results of the experimental testing with algorithms are presented and discussed. The performance of synchronisation results are calibrated by image inspection compared with theoretical counterparts. It is experimentally shown that the algorithm can handle data acquired both from GPS, GLONASS and Galileo with sufficient level of accuracy.

Study of Space-Surface Bistatic SAR Imaging Algorithms with COMPASS Signal

Based on Pseudo random noise codes of Chinese COMPASS Navigation Satellite System (CNSS), opened access at the end of 2012, space-surface bistatic synthetic aperture radar (SS-BSAR) passive imaging system is investigated. Furthermore, a modified Range Doppler (RD) algorithm that takes direct signal as reference signal in range compression is proposed. The good imaging performance of SS-BSAR system is demonstrated via modified RD algorithm simulation results.

SS-BSAR WITH GNSS AND A STATIONARY RECEIVER-EXPERIMENTAL RESULTS

This paper presents experimental results in the study of Space-surface Bistatic SAR (SS-BSAR) with global navigation satellite system (GNSS) and stationary receiver. The system uses GNSS as the transmitter of opportunity and a self-built, low cost receiver being set- up and flxed on the earth. It is potentially useful at remote sensing applications such as earth monitoring. The system prototype and signal processing at each stage leading to flnal image are described. Experimental image analysis is the core of this paper, and therefore performed in details flnally.

Image Formation Algorithm for Asymmetric Bistatic SAR Systems With a Fixed Receiver

This paper proposes a highly accurate bistatic range migration algorithm (RMA) for space-surface bistatic synthetic aperture radar (BiSAR) systems with asymmetric configurations when the transmitter moves along a rectilinear trajectory and the receiver stays at a fixed location. The main work here includes three aspects. First, by introducing a 2-D change of frequency variables, an analytical 2-D spectrum formula without any approximation was derived at the first time. Second, with the linearity approximation of the derived phase, a highly accurate bistatic RMA was proposed and guaranteed that the algorithm could be applied to focus the echo from a large target scene. Furthermore, the nonlinear phase of the linearity approximation was analyzed to avoid the defocus effect in the final BiSAR image. Both simulation and indoor experimental results are presented to validate our analysis.

Experimental Demonstration of Passive BSAR Imaging Using Navigation Satellites and a Fixed Receiver

This letter demonstrates the feasibility of space-surface bistatic synthetic aperture radar using navigation satellites as transmitters of opportunity and a fixed ground-based receiver. Experiments with real satellite signals are described, and the obtained imagery is presented and discussed.

Study of SAR imaging with COMPASS signal

A concept of space-surface bistatic synthetic aperture radar (SS-BSAR) passive imaging system is proposed, which is parasitic on the signal of COMPASS Navigation Satellite System (CNSS). The feasibility is demonstrated by analyzing the signal ambiguity function and the range resolution as well as the system topology. Due to the multiple peaks of signal in the auto-correlation function, a new correlation is used to remove the side-peaks. A double-channel receiver is employed to receive the direct satellite signal and the ground reflected signal. The direct signal is a reference signal in range compression, and may also be used for transmitter-receiver signal synchronization. The reflected signal is raw data collected for imaging. Then, a modified range-Doppler imaging algorithm is derived based on the system geometric models and BSAR imaging principle. The proposed algorithm is verified via signal simulation. The work in this paper is of great value to the further use of COMPASS signal, as well as other global navigation satellite signals in passive imaging.

Problem of signal synchronisation in space-surface bistatic synthetic aperture radar based on global navigation satellite emissions – experimental results

This study presents the synchronisation problem in ‘space-surface bistatic synthetic aperture radar (SS-BSAR)’ system. Global Navigation Satellite Systems (GNSS) are considered as transmitters of opportunity. It highlights various important issues of synchronisation, specifically related to SS-BSAR utilising GLONASS as the transmitter. Experimental testing of the synchronisation algorithm is described and verified using the GLONASS satellite. Also, experimental images obtained from GLONASS are presented and briefly analysed.

Space-Surface Bistatic SAR Image Formation Algorithms

This paper presents algorithms designed for a subclass of bistatic synthetic aperture radar (BSAR) called space-surface BSAR (SS-BSAR). Two SS-BSAR configurations are considered. The first one assumes a stationary, spaceborne transmitter and a moving airborne receiver. The second case is the generalized SS-BSAR configuration, where the transmitter is nonstationary. The transmitter and receiver have essentially different flight paths and velocities. For each configuration under investigation, the characteristics of the corresponding SS-BSAR received signal are examined first. Then, each proposed algorithm is derived analytically, and verified via simulation.

The possibility of isolated target 3-D position estimation and optimal receiver position determination in SS-BSAR

Starting from the generalized ambiguity function of bistatic SAR (BSAR), it is shown that 3-D point target estimation can be carried out in space-surface bistatic SAR (SS-BSAR). Appropriate analytical equations, based on maximum likelihood estimation (MLE), are derived and confirmed via computer simulation. Furthermore, the performance of the estimate using the Crammer-Rao bound is analyzed for the case in question, thus further revealing the possibility and potential of target 3-D position estimation. Setting the determinant maximum of the information matrix as the criterion, the optimal receiver position and multi-receiver configuration are analytically determined in the SS-BSAR system. Simulation results also validate the correctness of the analytical calculation.

Results of a Space-Surface Bistatic SAR Image Formation Algorithm

This paper reports progress in the development of an image formation algorithm suitable for stripmap space-surface bistatic synthetic aperture radar. A description of the proposed algorithm, which is a modification of the standard range-Doppler algorithm, is provided for the case when the transmitter and the receiver have parallel flight paths and unequal velocities. Both simulation and initial experimental results are presented to verify our analysis.

Space-surface bistatic synthetic aperture radar with global navigation satellite system transmitter of opportunity-experimental results

Progress in the study of space-surface synthetic aperture radar is presented. Global navigation satellite system is considered as the transmitter of opportunity. It highlights the various important issues to successfully obtain an image. The experimental testing of the imaging algorithm is presented and verified using a GLONASS satellite signal.