Multiple Azimuth Research Articles

Monitoring and Comparative Analysis of NO2 and HCHO in Shanghai Using Dual-Azimuth Scanning MAX-DOAS and TROPOMI

This study employed dual-azimuth scanning MAX-DOAS to monitor vertical column densities of NO2 and HCHO in Shanghai during the summer and winter of 2023, and compared the results with Sentinel-5P TROPOMI data. Dual-azimuth scanning revealed a generally consistent trend in gas concentrations (r > 0.95), but concentrations at 90° were higher than those at 0°, especially near the surface. This suggests that averaging multiple azimuth angles is necessary to better represent regional pollution levels. During the observation period, diurnal patterns revealed that NO2 exhibited a “double peak” in the morning and evening, which was more pronounced in the summer, while HCHO peaked between 13:00 and 15:00. Comparisons with the TROPOMI data demonstrated overall good agreement. However, the probability of TROPOMI’s NO2 and HCHO measurements being lower than those of MAX-DOAS was 80% and 62.5%, respectively. Furthermore, TROPOMI tended to overestimate at high concentrations, with overestimation reaching 41.14% for NO2 when exceeding 9.54 × 1015 molecules/cm2 and 25.93% for HCHO when exceeding 1.26 × 1016 molecules/cm2. Sensitivity analysis of the sampling distance (0–40 km) between TROPOMI samples and the ground-based site, and the sampling time (±5 to ±60 min) relative to the TROPOMI overpass, revealed that using a sampling distance of 15–25 km for NO2 and 10–20 km for HCHO, along with appropriately shortening sampling times in the winter and extending them in the summer, can effectively enhance the consistency between satellite and ground-based observations. These findings not only reveal the spatiotemporal distribution characteristics of regional pollutants but optimize the sampling time and distance parameters for satellite–ground observation validation, providing data support for improving and enhancing the accuracy of satellite retrieval algorithms.

Research on Azimuth DBF Method of HRWS SPC MAB SAR Imaging Mode with Non-Ideal Antenna Mode

Single-phase center multiple azimuth beam (SPC MAB) mode is an effective method for high-resolution wide-swath (HRWS) SAR imaging. The traditional azimuth spectrum reconstruction method for SPC MAB mode is based on the combination scheme from which fake targets along the azimuth direction arise because the inter-beam interference is not considered. When the real antenna mode is inconsistent with the ideal one, the disadvantages of the combination scheme become more serious. In this paper, based on the basic theory of the low-pass, band-limited, multiple-channel under-sampling and reconstruction, a novel digital beam-forming method is proposed for the SPC MAB imaging mode with ideal antenna mode first. The method analyzes the system functions of the sub-beams, based on which digital beam-forming filters are designed for all the sub-beams. The designed filters can reconstruct the correct wide-bandwidth azimuth spectrum and suppress the inter-beam interference simultaneously. Furthermore, the proposed method is extended to SPC MAB mode with the non-ideal antenna mode. The simulation experiments prove the validities of the proposed method both for azimuth spectral reconstruction and the inter-beams interfering suppressing, no matter that the SPC MAB’s antenna mode is ideal or non-ideal.

Using the Displaced Phase Center Azimuth Multiple Beams Technique with Spaceborne Synthetic Aperture Radar Systems for Multichannel Reconstruction of Accelerated Moving Targets

The displaced phase center multiple azimuth beams (DPCMAB) technique can help spaceborne synthetic aperture radar (SAR) systems obtain the high-resolution wide-swath (HRWS) imaging capacity, and azimuth multichannel reconstruction is usually required due to azimuth non-uniform sampling. Compared with stationary and moving targets, the range history and azimuth signal model of the moving target with an acceleration are obviously different. The azimuth multichannel signal model of an accelerated moving target is established, and the relationship between acceleration and Doppler parameters is analyzed. Furthermore, the impact of the acceleration on azimuth multichannel reconstruction and imaging results is simulated and analyzed. According to the azimuth multichannel signal model, an azimuth multichannel reconstruction approach for accelerated moving targets is proposed. The key point of the proposed reconstruction approach is the modified azimuth multichannel matrix, which is related not only to azimuth and slant velocities but also accelerations. The target’s velocities and accelerations are obtained using multiple Doppler parameter estimations. Compared with the conventional method of processing the raw data of accelerated moving targets, this proposed method could distinctly suppress image defocusing and pairs of false targets. Simulation results on point targets validate the proposed azimuth multichannel reconstruction approach.

Pattern evolution and modal decomposition of Faraday waves in a brimful cylinder

This paper investigates the steady-state pattern evolution of symmetric Faraday waves excited in a brimful cylindrical container when driving parameters much exceed critical thresholds. In such liquid systems, parametric surface responses are typically considered as the resonant superposition of unstable standing waves. A modified free-surface synthetic Schlieren method is employed to obtain full three-dimensional spatial reconstructions of instantaneous surface patterns. Multi-azimuth structures and localized travelling waves during the small-elevation phases of the oscillation cycle give rise to modal decomposition in the form of $\nu$ -basis modes. Two-step surface-fitting results provide insight into the spatiotemporal characteristics of dominant wave components and corresponding harmonics in the experimental observations. Arithmetic combination of modal indices and uniform frequency distributions reveal the nonlinear mechanisms behind pattern formation and the primary pathways of energy transfer. Taking the hypothetical surface manifestation of multiple azimuths as the modal solutions, a linear stability analysis of the inviscid system is utilised to calculate fundamental resonance tongues (FRTs) with non-overlapping bottoms, which correspond to subharmonic or harmonic $\nu$ -basis modes induced by surface instability at the air–liquid interface. Close relationships between experimental observations and corresponding FRTs provide qualitative verification of dominant modes identified using surface-fitting results. This supports the validity and rationality of the applied $\nu$ -basis modes.

Position‐only planar hexagonal array antenna pattern nulling with simultaneous side lobe reduction at multiple azimuth planes

SummaryThis article presents a study on the placement of multiple nulls as well as minimization of side lobe level in the radiation pattern using a planar hexagonal antenna array structure in two different vertical planes. The desired null depth is achieved to suppress the interference signal by the position‐only control of the uniformly excited isotropic antennas in the array structure. The immediate solution to the mentioned computational problem is reached by various meta‐heuristic optimization algorithms such as teaching learning‐based optimization (TLBO), symbiotic organism search (SOS), and moth fly optimization (MFO) within a considerably reduced processing time with a control over the design constrains. Various examples for diversified scenarios are demonstrated to place multiple deep nulls in the radiation pattern without compromising the pattern constraints and all other radiation pattern characteristics. This experiment sought to illustrate and quantify the unique benefits and limitations of proposed technique using three considered meta‐heuristic optimization algorithm.

A preliminary result of microtremor study to identify the subsurface condition in the Aceh Tenggara region

The Aceh Tenggara region is located in an tectonically active region and it can be categorized as the prone-area. Historically, there were many major earthquakes occured the active fault called the Tripa segment that has generated massive damages and losses. The study of the seismic vulnerability around the highly populated city in the Aceh Tenggara region, Kutacane City, as the center of economy and office activities must be conducted to prepare the suitable earthquake mitigation program. The microtremor have been recorded at 25 sites with one km grid interval between all points. The record lengths have 30 minutes duration at each site, and they were measured with the Taurus Seismometer in miniseed format. The data were analyzed by using the HVSRpy in order to obtain the Horizontal to Vertical Spectral Ratio for each site by means of the geometric-mean and the multiple azimuths methods. Both methods provided a similar result at both focuses with dominant frequency of 0.8 Hz at the AT01 site and 4.8 Hz at the AT14 location. The preliminary result shows that the higher dominant frequency were recorded along the southern part of the Kutacane city which is associated with the Alas formation.

A Robust Image-Domain Subspace-Based Channel Error Calibration and Postimaging Reconstruction Algorithm for Multiple Azimuth Channels SAR

High resolution and wide-swath imaging always suffer channel errors of the multiple azimuth channels (MACs) synthesis aperture radar (SAR). This article presents an image-domain channel error estimation algorithm based on image subspace least square (ISP-LS) method and a postimaging reconstruction algorithm for MACs SAR. The proposed method mainly consists of three parts: first, preprocessing and SAR imaging; second, the ISP-LS-based channel error estimation and calibration algorithm; third, postimaging reconstruction and ambiguity suppression. The channel phase and baseline errors are joint-estimated based on image subspace after SAR imaging, providing advantages that the higher signal-to-noise ratio (SNR) regions SAR images and the subspace method can be used to achieve a more accurate estimate with a relatively low computational load. We also propose a postimaging reconstruction method for ambiguity suppression, which can realize imaging each channel data and then combining the multichannel SAR images. Simulated and acquired airborne SAR data are processed to demonstrate the effectiveness of the proposed method.

Accurate detection method of moving target based on sequential SAR images with multiple azimuth squint angles

In this paper, a novel moving target detection method for sequential Synthetic Aperture Radar (SAR) images with different azimuth-squint angles is proposed. In sequential SAR images, due to the movement of the target, the imaging position of moving targets among different frames differs. The method proposed in this paper uses this kind of motion characteristics to achieve the detection of moving targets in multi-frame SAR images. This algorithm can be divided into two parts: block-level detection and pixel-level detection. Block-level detection is achieved by stacked denoising autoencoders to extract the high-dimensional features of the moving target. Pixel-level detection consists of Local Binary Similarity Patterns (LBSP) coding as well as grayscale background subtraction. Pixel-level detection only needs to consider the pixels of foreground image pieces which contain moving targets. This method can not only increase the detection speed, but also suppress the false alarm problem caused by clutter. Experiments are carried out for verifying the validation of the method and the comparison are made between the proposed method and the traditional Constant False Alarm Rate (CFAR) algorithm.

A Moving Target Velocity Estimation Method Based on the MC-MASA SAR Mode

Imaging position shift based on the multiple azimuth squint angles (MASA) mode is effective for target azimuth velocity estimation, whereas accuracy is low when target range velocity is high. In this paper, the estimation problem for both target azimuth and range velocities is considered based on the multi-channels MASA (MC-MASA) mode. Firstly, the acquisition geometry of MC-MASA mode and Doppler characteristics of a moving target are analyzed in detail, especially in squint mode. Then, for better moving target estimation, the stationary background clutter is removed using the displacement phase center antenna (DPCA) technique, and the failure in range velocity estimation with sequential SAR images is also discussed. Furthermore, a modified along-track interferometry (ATI) is proposed to preliminarily reconstruct the azimuth-and-range velocity map based on the MC-MASA mode. Since the velocity estimation accuracy is dependent on squint angle and signal-to-clutter ratio (SCR), the circumstances are divided into three cases with different iteration estimation strategies, which could expand the scene application scope of velocity estimation and achieve a high estimation accuracy along both azimuth and range directions. Finally, the performance of the proposed method is demonstrated by experimental results.

Multiple RFI Sources Location Method Combining Two-Dimensional ESPRIT DOA Estimation and Particle Swarm Optimization for Spaceborne SAR

Synthetic aperture radar (SAR) systems are susceptible to radio frequency interference (RFI). The existence of RFI will cause serious degradation of SAR image quality and a huge risk of target misjudgment, which makes the research on RFI suppression methods receive widespread attention. Since the location of the RFI source is one of the most vital information for achieving RFI spatial filtering, this paper presents a novel location method of multiple independent RFI sources based on direction-of-arrival (DOA) estimation and the non-convex optimization algorithm. It deploys an L-shaped multi-channel array on the SAR system to receive echo signals, and utilizes the two-dimensional estimating signal parameter via rotational invariance techniques (2D-ESPRIT) algorithm to estimate the positional relationship between the RFI source and the SAR system, ultimately combines the DOA estimation results of multiple azimuth time to calculate the geographic location of RFI sources through the particle swarm optimization (PSO) algorithm. Results on simulation experiments prove the effectiveness of the proposed method.

A Postmatched-Filtering Image-Domain Subspace Method for Channel Mismatch Estimation of Multiple Azimuth Channels SAR

Multiple azimuth channels (MACs) synthetic aperture radar (SAR) can theoretically achieve high azimuth resolution and wide swath (HRWS). Nevertheless, in practice, channel mismatch will lead to ghost or azimuth ambiguities, which will degrade the imaging quality. This article proposes a novel idea for estimating the channel mismatch of MACs SAR in the image domain. First, we found that the degree of freedom (DOF) of MACs signals doubles after signal reconstruction and imaging. As a result, when the channel number is not great enough, the subspace method for error estimation is unable to be implemented. To deal with this problem, we introduce a DOF compression method based on spectral filtering. This method can decrease the image-domain DOF. Finally, an image-domain subspace method is proposed to estimate the channel phase error, using the focused data and selecting the high SNR region of SAR images. The proposed method has advantages for the channel phase error estimation. Simulated space-borne MACs SAR data and real measured airborne SAR data are processed to demonstrate the effectiveness of the proposed method.

Drainage Ditch Berm Delineation Using Lidar Data: A Case Study of Waseca County, Minnesota

Within a drainage system, drainage ditches are designed to improve existing natural drainage. Although drainage ditches are mostly engineered, they can also be part of natural watercourses. For environmental sustainability, in many places there are guidelines to establish vegetative buffer strips along the boundary of drainage ditches. In this landscape planning study, a geospatial modeling framework was established to identify these drainage system landforms and the boundary that separates these landforms from their surrounding areas across Waseca County in south-central Minnesota. By employing almost 2000 GPS spot elevation measurements from five ditch systems and one-meter Light Detection and Ranging (LiDAR) derived digital elevation model (DEM) data, the drainage ditch berm polygons were delineated. Eight low light angle hillshade rasters at 45-degree azimuth intervals were used to construct the model. These hillshade rasters were combined to form a composite raster so that the effect of multiple azimuths can be captured during ditch berm delineation. The GPS points identified as the top of the berm were used to extract cell values from the combined hillshade. These cell values were modeled further using statistical distribution graphs. The statistical model derived +0.5 and +1 standard deviation values (cell values 812 and 827, respectively) of the combined hillshade raster were utilized to obtain complete berm polygons. In this semi-automated method, between 67.30% to 79.80% of ditch berm lengths were mapped with an average error that is less than the resolution of the DEM. Demarcation of these boundaries are important for local governments in Minnesota and throughout the world, as it could help guide land–water management and aid sustainable agriculture.

Evaluation of azimuth cement bond quality based on the arcuate phased array acoustic receiver station

Cement bond quality is a crucial parameter in oil production, and acoustic logging is among the main methods of evaluating this property. By analyzing the characteristics of casing and formation waves, the cement bond quality of the casing–cement interface (interface I) and cement–formation interface (interface II) can be evaluated. However, the use of both monopole sources and receivers render the evaluation of the azimuth and angle range of cement channeling difficult using conventional acoustic logging tools. Herein, we developed an improved azimuthally acoustic bond tool (AABT 2.0) comprising a monopole acoustic radiator and arcuate phased array (APA) acoustic receiver stations with enhanced azimuth resolution capability. AABT 2.0 can determine the azimuth and angle range of cement channeling and improve the resolution of azimuth measurement. We studied these factors through numerical simulation and physical experiments. Numerical simulation results show that the azimuth of cement channeling can be determined by measuring the amplitude of the casing wave's head wave in multiple azimuths received by the APA acoustic receiver stations in a casing well. Compared with individual-reception mode, APA acoustic receiver stations with the scanning-reception mode can both determine the azimuth of cement channeling more accurately and confirm the angle range of cement channeling. Data processing results from experimental wells show that AABT 2.0 can evaluate the cement bond quality of interface I with a high azimuth resolution in the circumferential and axial directions, through the amplitude imaging display of the casing wave's head wave. The reliability of AABT 2.0 and the accuracy of our measurement results are verified through comparison with results from an ultrasonic imaging logging tool and information concerning the well condition.

Parameter Extraction Based on Deep Neural Network for SAR Target Simulation

Synthetic aperture radar (SAR) image simulation can provide SAR target images under different scenes and imaging conditions at a low cost. These simulation images can be applied to SAR target recognition, image interpretation, 3-D reconstruction, and many other fields. With the accumulation of high-resolution SAR images of targets under different imaging conditions, the simulation process should be benefited from these real images. Accurate simulation parameters are one of the keys to obtain high-quality simulation images. However, it takes a lot of time, energy, and resources to get simulation parameters from actual target measurement or adjusting manually. It is difficult to derive the analytical form of the relation between a SAR image and its simulation parameter, so nowadays the abundant real SAR images can hardly help the SAR simulation. In this article, a framework is proposed to obtain the relationship between SAR images and simulation parameters by training the deep neural network (DNN), so as to extract the simulation parameters from the real SAR image. Two DNNs, convolutional neural network (CNN), and generative adversarial network (GAN) are used to implement this framework. By modifying the network structures and setting reasonable training data, our DNNs can learn the relationship between image and simulation parameters more effectively. Experimental results show that the DNNs can extract the simulation parameters from the real SAR image, which can further improve the similarity of the simulation image while automating the setting of simulation parameters. Compared with CNN, the simulation parameters extracted by GAN can achieve better results at multiple azimuth angles.

Daytime Cloudless Sky Radiance Quantification with Ground-Based Aerosol and Meteorological Observations in the Shortwave Infrared

AbstractDaytime spectral sky radiance, or sky brightness, is deceptively complex to predict accurately. The Laser Environmental Effects Definition and Reference (LEEDR) first-principles atmospheric model propagates the spectral radiance of the sun to a sensor by modeling the scattering, absorption, and transmission of the radiated light through representative atmospheric layers. For this application, LEEDR was used to ingest numerical weather prediction (NWP) models, and scale the boundary layer and incorporate aerosol loading with ground-based measurements. This study compares LEEDR-derived spectral sky radiance simulations that include measured climatological, measured meteorological, and aerosol loading data to direct sky radiance measurements. Direct measurements of the daytime sky are accomplished with a 1-m-aperture telescope and simultaneous I-band and J-band camera observations (~0.8 and ~1.2 μm, respectively). LEEDR models of the daytime sky are compared to I-band and J-band radiances at multiple azimuths, elevations, and observation times. Residual error analysis is used to determine the accuracy of models including numerical weather prediction data, historical climatology, scaled aerosol loading via in situ particle count measurements, and meteorological updates. Key findings motivate the inclusion of real-time particle count measurements into future daytime sky radiance models for increased scattering accuracy via realistic atmospheric aerosol loading.

Feature-Compression-Based Detection of Sea-Surface Small Targets

This paper aims to develop a feature-based detector using seven existing salient features of radar returns to improve the detection ability of high-resolution maritime ubiquitous radars to sea-surface small targets. Maritime ubiquitous radars form simultaneously dwelling beams at multiple azimuths by digital array receiver and allow long observation time for detection. Due to absence or incompletion of training samples of radar returns with various types of sea-surface small targets, the detection boils down to designing a one-class classifier in the seven-dimensional (7D) feature space mainly by using training samples of sea clutter. A feature compression method, though maximizing interclass Bhattacharyya distance, is proposed to compress the 7D feature vector into one 3D feature vector with the help of simulated radar returns of typical targets. In the compressed 3D feature space, a modified convexhull learning algorithm is given to determine one convex polyhedron decision region of sea clutter at a given false alarm rate. In this way, a feature-compression-based detector is constructed, which can exploit more features of radar returns to improve detection performance. It is verified by the recognized and open IPIX and CSIR radar databases for sea-surface small target detection. The results show that it attains obvious performance improvement.

High-Resolution Wide-Swath IRCI-Free MIMO SAR

A frequency-domain system identification-based multiple-input multiple-output (FDSI-MIMO)-SAR algorithm using multiple phase center multiple azimuth beams is proposed to obtain high-resolution wide-swath (HRWS) imaging. Frequency-division multiple access is used in such a way that each transmitter emits a conventional linear frequency-modulated (LFM) waveform modulated by a different carrier frequency and the obtained range resolution corresponds to the total transmitted bandwidth. In this article, an MIMO-SAR problem is modeled, using the principle of displaced phase center, as multiple but separate multiple-input single-output (MISO) system identification problems. The channel impulse responses of the individual MISO problems are identified in the range dimension using an FDSI-based estimation algorithm in such a way that the estimated range profile is free of interrange cell interference. In addition, the proposed algorithm does not require separating the subband waveforms at the receiver as they are processed jointly without a need to add guard bands between the adjacent subbands, which would allow utilizing the available bandwidth to the maximum efficiency. The method of synthesizing a wide transmit antenna beam from a narrow antenna beam applied in single-input multiple-output (SIMO) SAR is extended to MIMO SAR to remove the sidelobes effects of the receive beams and hence leading to the desired signal-to-noise ratio. A pulse repetition frequency lower than the Doppler bandwidth is used to obtain wide swath without experiencing aliasing in the Doppler spectrum. Finally, both simulated and constructed raw data are used to validate the effectiveness of the proposed algorithm.

Modelling analysis of the limitation of P-wave AVAZ inversion

The limitation of P-wave amplitude versus azimuth (AVAZ) inversion for fracture attribute parameters was studied by numerical modeling. First, seismic reflection data from multiple azimuths and incident angles were synthetized using anisotropic elastic wave equation modeling performed on a geological model, with a homogeneous isotropic medium overlying an anisotropic medium comprising vertical fractures. Then AVAZ inversion for fracture attribute parameters was performed on the synthetic data, from noise free to a signal-to-noise ratio (SNR) level of 2. The results were analyzed by comparison with the actual attribute parameters of the model. We demonstrate that the fracture azimuth attributes from the AVAZ inversion of noise free data agree well with the actual models, with difference <1°, over incident angle range from 9.8° to 44.2°. Inversion results from noisy data, on the other hand, vary widely and failed to characterize the actual azimuth, though an average of many inversions may still be able to approximate azimuth. In contrast, fracture intensity attributes from AVAZ inversion generally carry large inherent errors. The AVAZ attributes from noise free data underestimate the intensity, using incident angle range of 15° to ~26°, with errors ranging from 8% to ~92%. Using a lager incident angle, within ~26° to 35°, overestimates the intensity, with errors up to ~461%. The inherent errors are so large and variable that the fracture intensity attributes from AVAZ inversion are not suitable for use as direct quantitative interpretation of fracture intensity. However, the relative differences of fracture intensity attributes from AVAZ inversion qualitatively agree with the actual intensity differences and may be exploited as a qualitative measure of fracture intensity variation applied to a very limited range of incident angles. For noisy data, it is difficult to characterize fracture azimuth, not only by a single inversion but also by a statistical mean of multiple inversion results and an effective de-noising processing strategy is a critical step for fracture azimuth inversion.

An investigation of seismic anisotropy in the lowermost mantle beneath Iceland

SUMMARYIceland represents one of the most well-known examples of hotspot volcanism, but the details of how surface volcanism connects to geodynamic processes in the deep mantle remain poorly understood. Recent work has identified evidence for an ultra-low velocity zone in the lowermost mantle beneath Iceland and argued for a cylindrically symmetric upwelling at the base of a deep mantle plume. This scenario makes a specific prediction about flow and deformation in the lowermost mantle, which can potentially be tested with observations of seismic anisotropy. Here we present an investigation of seismic anisotropy in the lowermost mantle beneath Iceland, using differential shear wave splitting measurements of S–ScS and SKS–SKKS phases. We apply our techniques to waves propagating at multiple azimuths, with the goal of gaining good geographical and azimuthal coverage of the region. Practical limitations imposed by the suboptimal distribution of global seismicity at the relevant distance ranges resulted in a relatively small data set, particularly for S–ScS. Despite this, however, our measurements of ScS splitting due to lowermost mantle anisotropy clearly show a rotation of the fast splitting direction from nearly horizontal for two sets of paths that sample away from the low velocity region (implying VSH &amp;gt; VSV) to nearly vertical for a set of paths that sample directly beneath Iceland (implying VSV &amp;gt; VSH). We also find evidence for sporadic SKS–SKKS discrepancies beneath our study region; while the geographic distribution of discrepant pairs is scattered, those pairs that sample closest to the base of the Iceland plume tend to be discrepant. Our measurements do not uniquely constrain the pattern of mantle flow. However, we carried out simple ray-theoretical forward modelling for a suite of plausible anisotropy mechanisms, including those based on single-crystal elastic tensors, those obtained via effective medium modelling for partial melt scenarios, and those derived from global or regional models of flow and texture development in the deep mantle. These simplified models do not take into account details such as possible transitions in anisotropy mechanism or deformation regime, and test a simplified flow field (vertical flow beneath the plume and horizontal flow outside it) rather than more detailed flow scenarios. Nevertheless, our modelling results demonstrate that our ScS splitting observations are generally consistent with a flow scenario that invokes nearly vertical flow directly beneath the Iceland hotspot, with horizontal flow just outside this region.

A Novel Wide Area Multiple Azimuth Beam ISAR Imaging System

A novel multiple azimuth beams (MAB) inverse synthetic aperture radar (ISAR) system, as well as, the corresponding processing algorithms are proposed in this paper, which is a promising technology for wide area surveillance (WAS). This system concept is intended to obtain wide area ISAR images of multiple moving targets, which would greatly increase the surveillance velocity range compared with the single beam system. The antenna transmits a sequence of high-gain and narrow radar beams to quickly scan a wide area, and receives the echoes from all the subswaths simultaneously. Two processing methods based on digital beamforming (DBF) are presented to separate the overlapped signals for achieving the wide area ISAR images. The performance of the proposed system is analyzed from the perspectives of the surveillance area, surveillance velocity range, and steering angle error. Finally, an exemplary ISAR system is presented and verified by the simulation experiments.