This letter proposes a coherent integration approach for weak target detection with constant radial jerk in a low signal-to-noise (SNR) environment. In the proposed approach, the second-order Keystone transform (SoKT) is first employed to correct the quadratic range migration (QRM) induced by the radial acceleration of a target. Next, a velocity-jerk matched filter is constructed to eliminate the residual target radial velocity and jerk terms. Finally, the coherent integration is achieved through non-uniform fast Fourier transform (NuFFT) along the slow time. Compared with the conventional methods, the proposed approach can obtain comparable accumulation performance with a lower computational complexity. Simulation and real-measurement experiments are conducted to demonstrate the effectiveness and reliability of the proposed approach in low SNR environments.

Employing azimuth multi-channel array configuration can effectively enhance the high-resolution and wide swath - synthetic aperture radar (HRWS-SAR) imaging performance by increasing the spatial sampling frequency along the azimuth direction. 1However, the ground moving targets with unknown radial velocities, may induce azimuth "ghost" points in a well-focused HRWS-SAR image with the imaging function related to ground static scene. To address this issue, the paper introduces a novel ground moving target imaging method in a multi-channel HRWS-SAR system. The multichannel HRWS-SAR simulation results verify the effectiveness and feasibility of the proposed method.

A spaceborne bistatic surveillance radar system, which may increase the target radar cross section through a large bistatic angle, can effectively improve the performance of small air moving target indication. However, due to the separation of the transmitter and the receiver, the clutter exhibits severe range dependence in both Doppler and spatial-angle domains. This may significantly decrease the number of independent identically distributed samples and, thus, cause the degradation of clutter suppression performance. In addition, when an air moving target flies above the sea, the broadened spectrum of sea clutter caused by the random intrinsic motion will further influence the clutter suppression performance. To deal with these problems, this article establishes a multichannel sea clutter model for a spaceborne bistatic surveillance radar system. The calculation of the positions of the iso-range contours is analyzed first. Then, the bistatic sea clutter model is established based on the directional wave spectrum, the monostatic–bistatic equivalence theorem, and the two-scale scattering model, where the Earth rotation and the range ambiguity of clutter are considered. Finally, the range dependence and the spectrum characteristics of bistatic sea clutter are discussed, and the clutter suppression performances under different azimuth bistatic angles, different elevation angles, and different sea states are analyzed. In addition, the influence of clutter range ambiguity is analyzed based on the simulations.

To achieve tight beam coverage and obtain the optimal target detection performance for a space-based early warning radar (SBEWR) system, the reasonable radar beam design is prerequisite. In this paper, an optimal beam position design algorithm in a SBEWR system is proposed, where the beam position overlap rate (BPOR) choice is reasonably designed. In the proposed algorithm, the maximum signal-to-clutter and noise ratio (SCNR) of the targets located at the beam position edge is chosen as the criterion for the BPOR optimization design. The BPOR designment result provides important guidance and references for beam filling designment and guarantee the effective target detection capability of a SBEWR system.

Due to existence of the long along-track baseline (ATB) between the satellites in a distributed space-based early warning radar (DSBEWR) system, a large number of grating lobes appear in radar returns, causing the noncontinuous detection phenomenon of an aerial moving target (AMT). To solve this problem, in this paper, a novel approach for ATB distribution design in a muti-satellite DSBEWR system is proposed. In the proposed algorithm, to reduce the amount of spatial ambiguity points located at the main-lobe region, the main-lobe gain of the received antenna pattern in the azimuth dimension is designed to be maximum via the non-uniformly intersatellite ATB designment. The effectiveness of the proposed method is verified by the simulated multi-channel radar data in a DSBEWR system.

As one of the main statistical characteristics of clutter, the clutter amplitude distribution plays an important role in the accurate modeling of spaceborne multi-channel radar signal as well as the subsequent, maritime radar target detection. In this paper, considering that the space-time adaptive processing (STAP) technology is usually applied to accomplish the main-lobe clutter rejection in a space-borne surveillance radar, the influence of different clutter amplitude distributions on STAP in a spaceborne multichannel radar system are analyzed. Firstly, a spaceborne multi-channel clutter model is established based on radar equation and clutter space-time steering vector. Then, Rayleigh distribution, Weibull distribution, lognormal distribution, K distribution, generalized Pareto distribution, and IG-CG distribution are used to fit the clutter amplitude. Finally, the effects of these clutter amplitude distributions on STAP performance are analyzed, respectively. The simulation results show that in the case of the same clutter power, the influence of different clutter amplitude distributions on STAP performance is approximately the same.

For air moving target indication in nadir region, due to the fact that a spaceborne radar beam can illuminate the top of fuselage, the target radar cross section is usually high, which is beneficial for the detection of a low-observable target. However, due to the short slant range, specular reflection effect, and relatively low radar ground resolution, the power of clutter component from nadir region is comparatively high, leading to the insufficient clutter suppression and the degradation of target detection performance. Fortunately, when an air moving target is adequately high, the target echo is able to be separated from the main clutter echoes due to a shorter time delay, making it possible to be only mixed with low-power ambiguous clutter echoes. Based on these considerations, this paper analyzes the performance of air moving target indication in nadir region for a spaceborne surveillance radar system. It analyzes the target minimum detectable velocities with different target heights and beam center elevation angles. Also, an effective sample selection method based on adaptive range segmentation is proposed to solve the power heterogeneity issue between the main clutter area and the range ambiguous clutter area. As a conclusion, the larger the elevation angle of an air moving target is, the higher the minimum target detectable height is.

Multiple-input–multiple-output (MIMO) technique has recently received great attention due to its promising prospect for ground moving target indication (GMTI) applications in a synthetic aperture radar (SAR) system. In this article, an SAR-GMTI processing technique in an MIMO-SAR system with dual-channel configuration is proposed. In the proposed method, up and down chirps are adopted as the transmitted waveforms. Then, the baseline estimation and clutter rejection are simultaneously accomplished in the raw Doppler data domain, after which two separated range-compressed echo signals corresponding to two transmitters can be obtained without the influence of cross-correlated interferences of the clutters. Subsequently, a ground moving target can be detected, clustered, finely refocused based on the Doppler chirp parameter estimation, and accurately relocated by using the along-track interferometry (ATI) processing technique. Simulated experiments are implemented to validate and evaluate the feasibility of the proposed method.

Due to the existence of the time synchronization error, the correlation coefficient between the main satellite and auxiliary satellite severely declines, thus deteriorating the clutter suppression ability and aerial moving target indication (AMTI) performance in a distributed space-based early warning radar (DSBEWR) system. In this paper, a novel algorithm is proposed to estimate and calibrate the linear time synchronization error. In the proposed algorithm, the rough linear time synchronization error range is firstly estimated according to the Doppler offset between the same spatial channel in the main satellite and the auxiliary satellite. After obtaining the searched rough error range, the linear time synchronization error can be accurately obtained by finding the max correlation coefficient between the main satellite and auxiliary satellite after performing time synchronization error compensation. The effectiveness of the proposed method is verified by the simulated multi-channel radar data in a DSBEWR system.

Due to existence of the long along-track baseline (ATB) in a distributed space-based early warning radar (DSBEWR) system, a large number of grating lobes appears in both main-lobe and side-lobe clutter regions, causing the discontinuously detectable phenomenon of an aerial moving target (AMT). To solve this problem, in this paper, a novel spatial ambiguity suppression algorithm is proposed. In the proposed algorithm, based on the prior information provided by the system parameters and the signal processing results from the single satellite radar data, after performing the multi-channel clutter rejection, the spatial ambiguity can be eliminated via the joint processing of residual clutter signals corresponding to the single satellite and the muti-satellites. Simulated processing results are provided to validate the effectiveness of the proposed method.

Geosynchronous spaceborne-airborne bistatic synthetic aperture radar (GEO-BiSAR) has the advantages of wide beam coverage, long exposure time, and superior system flexibility. However, it is a challenge for GEO-BiSAR to efficiently acquire SAR images both with high resolution and wide swath due to the severe range and azimuth spatial variances. To deal with this issue, a modified Omega-K method is proposed in this paper. In the proposed algorithm, an equivalent range model associated with GEO-BiSAR configuration is built, where the equivalent parameters of the airborne radar receiver absorb the phase parameters corresponding to the GEO transmitter. Then, the Stolt interpolation is performed to realize the range-azimuth decoupling, achieving the linearization between range and frequency variables. Finally, a well-focused SAR image could be obtained after residual spatial variance error compensation. Simulations are presented to demonstrate the effectiveness of the proposed method.

By transmitting the constant pulse repetition interval (PRI) sequence, the traditional synthetic aperture radar (SAR) system will suffer from the loss of coverage in elevation. Thus a staggered-SAR system is developed in recent years, which employs the continuously PRI-varied sequence, making the blind ranges locate at different regions in different receive instant. However, the nonuniformly sampled signal will cause ambiguities in the SAR imaging result. To deal with this issue, in this paper, a novel signal restoration method based on kernel regression is proposed to resample the nonuniform signal. Real-measured spaceborne SAR data is used to validate the proposed method.

Next-generation SAR imaging system demands wide-swath and high resolution to observe Earth's surface, promoting the development of the high-resolution and wide-swath (HRWS) synthetic aperture radar (SAR) system working in terrain observation by progressive scans (TOPS). However, Doppler ambiguities will occur in this system, causing the imaging performance severely degrading. To address this issue, in this paper, a novel Doppler ambiguous suppression method for an HRWS-TOPS SAR system based on the orthogonal projection subspace is developed. The effectiveness of the proposed method is verified by both the simulated and real SAR data.

The marine moving target detection is a very attractive research field in recent years. However, due to the existence of sea clutter with complex internal motion, the traditional space-time adaptive processing (STAP) methods may not obtain good processing performance. In this paper, the multichannel sea clutter is modeled and the time-varying and space-varying properties of sea clutter are analyzed. In addition, the time-frequency distribution characteristics of sea clutter are analyzed. Finally, a multichannel sea clutter suppression method based on short-time Fourier transform is proposed. The simulation results show that the proposed method can achieve better sea clutter suppression performance than that of the traditional STAP method.