Ground Moving Target Indication Mode Research Articles

A high precision estimation algorithm for multi‐channel wide‐area surveillance ground moving target indication mode based on maximum likelihood method

AbstractA high precision estimation algorithm for ground moving targets in multi‐channel wide‐area surveillance ground moving target indication systems is proposed based on maximum likelihood method. The main concept of this novel algorithm is to estimate the azimuth angle of the detected targets using maximum likelihood method with the space steering vector formed by the estimated interferometric phase extracted from the mainlobe clutter region of the real data. Through this novel algorithm, the effect of channel errors among the multi‐channels can be well reduced. Simulation experiments demonstrate the effectiveness of the proposed algorithm.

항공기 AESA 레이다에서 TWS를 이용한 지상 이동 표적 추적

A target-tracking method using the ground moving target indicator (GMTI) mode on active electronically scanned array (AESA) radar is proposed. The GMTI mode can operate in wide ground areas. However, the 3-dB beamwidth of the X-band radar is narrow, and a target is detected on multiple adjacent beams. To delete overlapping target plots, beam-to-beam processing considering a real-time system is proposed. In addition, a track while scan (TWS) multiple-target-tracking algorithm was constructed for the system. Through a flight test with true car mounted GPS, it was confirmed that the real-time processing ability and target-tracking performance of the GMTI algorithm were satisfactory.

Adaptive Doppler Compensation for Mitigating Range Dependence in Forward-Looking Airborne Radar

In this paper, we present ground moving target indication (GMTI) signal processing algorithm encompassing clutter suppression, target detection and parameter estimation. One of the most significant yet least publicized is the need of the GMTI mode for a forward-looking airborne radar. The integration of GMTI mode in a forward-looking airborne radar allows reconnaissance and surveillance operations in all weather conditions. In this context, space time adaptive processing (STAP) offers a unique prospect of enabling the GMTI mode in forward looking airborne radar. STAP is a two-dimensional filter designed to suppress platform motion-induced clutter Doppler spread. Interference is characterized by a covariance matrix. In the case of a forward-looking airborne radar, the clutter Doppler is dependent on range. Clutter Doppler dependency on the range renders the training cells heterogeneous. The heterogeneity effects are particularly prominent in the near range bins. Non-homogeneous training cells have a deleterious effect on STAP performance. In this study, we propose an adaptive Doppler compensation to mitigate the degraded STAP performance in the near range bins. The adaptivity feature circumvents the need for the availability of radar parameters in real-time. The real time implementation of STAP is impeded by requirements of a large number of training samples and covariance matrix inversion. Therefore, there is a dire need to devise a framework to detect and estimate target parameters within the STAP. In this regard, we propose an efficient STAP algorithm to detect and estimate target parameters. STAP weights are applied to the input data to obtain a 3D array. The range projection of the 3D array is utilized to detect and estimate the range of the target, while the angle–Doppler projection is used to estimate spatial and temporal parameters of the target. Most of the literature on STAP is geared towards a known covariance matrix. The assumption of a known covariance matrix may degrade STAP performance because of the inherent mismatches between the actual and assumed target steering vectors. In this study, we estimate the covariance matrix based on the synthetic data generated from a model of an airborne phased array radar. The developed STAP algorithms closely mimic a real-time implementation scheme in an airborne radar platform. The results of the proposed algorithm are validated through target parameter estimation and STAP metrics on synthetic data.

GMTI and Parameter Estimation for MIMO SAR System via Fast Interferometry RPCA Method

Multiple-input multiple-output synthetic aperture radar (MIMO SAR) system has drawn considerable attention because of its extra degrees of freedom for high resolution and wide swath compared with the traditional multichannel SAR system. But how to extract the matched signal without the unmatched interferences is the foremost task for MIMO SAR system. In this paper, by using the orthogonal frequency division multiplexing chirp signals as the transmitted signals, it is demonstrated that the robust principal component analysis (RPCA) method can be successfully employed for ground moving target indication (GMTI) with no need for separating the matched signal and unmatched interferences. It is because the unmatched interference is proven to have low-rank property and noise-level magnitude, which can be separated apart from the matched signal with the RPCA method. However, the traditional RPCA methods may be restricted by the high computational burden due to the complex decompositions and multiple iterations. Hence, a fast interferometry RPCA method is proposed specially for GMTI mode, which takes full advantage of the characteristics of along-track interferometry SAR system. It can improve the probability of detection under low signal-to-clutter-and-noise ratio. Additionally, it will dramatically shorten the computational time. Furthermore, the proposed method can also estimate the radial velocities of the moving targets simultaneously. The results by applying the proposed method into a set of real SAR data are consistent with the analysis presented in this paper.

항공기 레이다의 GMTI 모드를 위한 Sigma-Delta STAP의 적용 설계와 성능 분석 시뮬레이션

Applications of Sigma-Delta STAP, and a method of GMTI processing are presented for GMTI(Ground Moving Target Indication) mode of airborne radar with sigma, delta, and guard channels. We showed results of performance analyses of presented methods by clutter simulation with ICM(Internal Clutter Motion), signal processing simulation and MDV(Minimum Detectable Velocity). Presented methods for Sigma-Delta STAP and GMTI processing are easy to apply practically in GMTI mode of airborne radar without restriction by specific airborne radar system.

Exploitation of the COSMO-SkyMed SAR System for GMTI Applications

The focus of this paper is on the exploitation of COSMO-SkyMed spotlight SAR images for Ground Moving Target Indication (GMTI). To this purpose, a two-step processing chain is proposed: the first step performs stationary clutter removal, whereas the second step performs moving targets detection. Both the steps are based on the use of a bank of focusing filters, each one matched to a different relative speed between the radar antenna and the target, here implemented as Chirp Scaling Algorithms in order to keep low the computational burden. The performance of the proposed technique is investigated by applying it to COSMO-SkyMed Single Look Complex spotlight SAR images and compared to theoretical performance: the analysis shows the effectiveness of the proposed technique in suppressing the stationary clutter and providing a high gain in signal to background power ratio, thus allowing subclutter visibility despite the single-channel nature of COSMO-SkyMed data. Moreover, the information provided by the bank is used to estimate the target motion and, by using a knowledge-based approach, relocate in along-track direction the detected movers. The shown results prove the feasibility of a GMTI mode for the COSMO-SkyMed SAR system and more in general for single-channel spaceborne systems.

Unambiguous across‐track velocity estimation of moving targets for multichannel synthetic aperture radar‐ground moving target indication systems

In this study, a method of estimating unambiguous across-track velocity of moving targets is presented. The method can be used for ground moving target indication mode of multichannel synthetic aperture radar (SAR) systems. The basic idea is to decompose the unambiguous velocity into the fractional and the integer parts, and to estimate them individually. As such, an integrated velocity estimation scheme is proposed. In the scheme, the idea of clutter suppression interferometry is adopted to estimate the fractional velocity part via the along-track interferometry technique. For estimating the integer velocity part, the ideas behind the multilook beat frequency are adapted and applied to coarsely estimate the unambiguous velocity first, and then the coarsely estimated unambiguous velocity is combined with the fractional velocity part to obtain an estimate of the ambiguity number. Finally, the ambiguity number and the fractional velocity part are combined to otain an accurate estimate of the unambiguous velocity. The proposed algorithm is tested with real SAR data. The results show that the integrated scheme represents an accurate solution to the unambiguous across-track velocity estimation problem.

A Research on Moving Target Trajectory Simulation and Tracking in Wide Area Surveillance Ground Moving Target Indication Mode

由于可以在较短时间内对大范围区域进行动目标监视，广域监视动目标检测(Wide Area Surveillance, WAS-GMTI)模式已经成为机载监视雷达的一种重要工作模式。目前具备WAS-GMTI工作模式的系统较少，实际数据较难获得，严重影响了对WAS-GMTI中相关处理算法的验证。该文提出一种基于电子地图路网信息的WAS-GMTI动目标点迹仿真方法。该方法根据载机和电子地图路网信息直接产生动目标信息，避免了仿真场景回波所需的大量运算，而且产生的动目标信息可以合理地融合到真实地理环境中。此外，联合对同一动目标的多次观测信息，该文还给出了一种动目标的轨迹关联方法。仿真结果验证了该文所提方法的有效性。

Error Analysis of Fast-moving Target Geo-location in Wide Area Surveillance Ground Moving Target Indication Mode

广域监视动目标检测(WAS-GMTI)模式作为机载监视雷达的一种重要工作模式，可以在较短时间内对大范围区域进行动目标监视，并进而对检测到的动目标进行快速定位，但在实际工程实现中，动目标的定位受到诸多因素的影响，直接使用理想公式对动目标进行定位存在较大误差。从战场或者交通监测的需求出发，广域监视动目标检测模式下需要对检测到的动目标进行快速定位。该文根据机载广域监视动目标检测模式下可以获得的动目标信息的特点，采用一种快速定位方法实现动目标的定位。同时对实际存在的导致动目标定位误差的这些因素进行了分析，并在考虑这些因素之后对动目标进行了重新定位。仿真和实测数据验证了该文对动目标定位误差的分析的合理性。

Experimental Verification of SAR-GMTI Improvement Through Antenna Switching

Recently, theoretical investigations have shown that switching between parts of the transmit and/or receive aperture in a pulse-to-pulse cycle may improve the ground moving target indication (GMTI) performance of a two-channel radar system. This paper intends to verify these findings experimentally for the switching concept for the first time. Accordingly, six different GMTI modes were implemented in the system PAMIR (phased-array multifunctional imaging radar) of the Fraunhofer Institute for High Frequency Physics and Radar Techniques (Fraunhofer FHR) including three switching modes. An experiment was conducted using six cooperative vehicles following a predefined scenario to compare the GMTI performance and, in particular, the positioning accuracy of the different GMTI modes. The results of this experiment as well as the underlying signal processing are presented in this paper. The analysis is based on a multilook constant false-alarm rate detection scheme. Due to the heterogenous nature of the considered scene, the well-known test statistic for homogeneous terrain had to be extended accordingly, and a novel test statistics is proposed.

Wide-Area Traffic Monitoring With the SAR/GMTI System PAMIR

This paper presents a wide area traffic monitoring experiment under real conditions, using the scan-MTI mode of the airborne radar sensor PAMIR. This flexible GMTI (Ground Moving Target Indication) mode was designed in order to rapidly monitor wide areas for moving targets. The scan operation enables the detection of targets from different aspect angles with a high revisit rate. The parameters (e.g., radial velocity, signal-to-noise ratio, and positioning accuracy) of the detected vehicles are investigated and compared to the expected theoretical GMTI performance. It will be shown that the scan-MTI mode is particularly adapted to perform an efficient wide-area traffic monitoring.

X-band experimental airborne radar – Phase II: synthetic aperture radar and ground moving target indication

Defence Research and Development Canada, Ottawa, has completed Phase II of a multifunction X-band wideband experimental airborne radar. The system consists of a high average power transmitter, a digital waveform generator, two wideband 8-bit channels for synthetic aperture radar (SAR)/inverse synthetic aperture radar and two narrowband 14-bit channels for ground moving target indication (GMTI). The reflector antenna uses a novel multimode feedhorn to derive two phase centres displaced in azimuth. The radar was designed to support research into SAR imaging of fixed and moving targets (ocean and land), time–frequency analysis of moving targets, clutter suppression for GMTI radar and ocean surveillance for small and large target detection. Highlights of the data collection capabilities, include a swath width 16 K points wide in the single-channel SAR modes, 8 K points wide in the two-channel integrated SAR–GMTI modes and 4 K points wide in the GMTI surveillance modes. The architecture of the radar, its modes of operation with respect to the SAR and GMTI data collection capabilities, the MATLAB-based GMTI processor, and the real-time kernel developed for the SAR processor are discussed; and results from its high resolution stripmap, landspot, seaspot and GMTI modes are presented from trials in July 2003.

X-band wideband experimental airborne radar for SAR, GMTI and maritime surveillance

Defence Research and Development Canada - Ottawa has completed Phase I in the development of a new multimode X-band wideband experimental airborne radar (XWEAR) to support studies in synthetic aperture radar (SAR) imaging, inverse SAR (ISAR), ground moving target indication (GMTI) radar and maritime surveillance radar with particular focus on small target detection and long-range surface surveillance. Specific areas of interest include research into SAR imaging techniques for fixed and moving targets, time–frequency analysis of ocean and land moving targets, space–time adaptive processing for application to GMTI, investigation into the electromagnetic backscatter properties of the ocean surface, generation of signatures for automatic target recognition and feature extraction, and analysis on the immunity of wide bandwidth systems against electronic countermeasures. Phase I culminated with the flight trialling of the SAR and maritime surveillance modes. Phase II will see the trialling of the wide area surveillance GMTI (WAS GMTI) and integrated SAR–GMTI modes. A description of the experimental radar is given along with an overview of its data collection capability. Distinguishing features include operation at X-band, single-channel operation for SAR and maritime surveillance, and two-channel operation for WAS-GMTI and integrated SAR–GMTI. The new radar maximises the use of an existing digital scan converter as a controller, and commercially available components including the transmitter, A/D converters and computer boards. The timing circuitry, waveform generator, single- and dual-channel receivers are custom built.