1986 International Conference on Parallel Processing

: Digital signal processing techniques expand the capabilities of modern radars. The central algorithm of radar signal processing is the fast Fourier transform (FFT). However, each radar has several modes and in most cases, environmental factors such as noise and clutter background are not completely understood. For this reason, flexibility of the signal processor is desirable. A method of gaining this flexibility is via general purpose (i.e., programmable) digital signal processing computer structures. In this note, a variety of such structures, both programmable, yet suitable for high speed FFT, are expanded.

The usage of a hypersonic platform for remote sensing application has promising prospects, especially for hypersonic platform-borne synthetic aperture radar (SAR) imaging. However, the high-speed of hypersonic platform will lead to extreme friction between the platform and air, which will cause the ionization of air. The ionized gas forms the plasma sheath wrapped around the hypersonic platform. The plasma sheath will severely affect the propagation of SAR signal and further affect the SAR imaging. Therefore, hypersonic platform-borne SAR imaging should be studied from a physical perspective. In this paper, hypersonic platform-borne SAR imaging under plasma sheath is analyzed. The SAR signal propagation in plasma sheath is computed using scatter matrix method. The proposed SAR signal model is verified by using a ground experiment system. Moreover, the effect of attenuation caused by plasma sheath on SAR imaging is studied under different SAR parameters and plasma sheath. The result shows that attenuation caused by plasma sheath will degrade the SAR imaging quality and even cause the point and area targets to be submerged into the noise. The real SAR images under plasma sheath also illustrate this phenomenon. Furthermore, by studying imaging results under different SAR and plasma parameters, it can be concluded that the severe degradation of SAR imaging quality appears at condition of high plasma sheath electron density and low SAR carrier frequency. The work in this paper will be beneficial for the study of hypersonic platform-borne SAR imaging and design of hypersonic SAR imaging systems in the future.

On the basis of the theory of microwave scattering from the ocean surface the correlation function of the synthetic aperture radar (SAR) signal intensity was obtained as a sum of two items. The first item is the proper image correlation function, i.e. the correlation function free of speckle noise SAR signal intensity, which has been investigated in many works (mostly by Alpers et al.). The second item describes the speckle structure in the image. It has been shown that at sufficiently large values of the well‐known velocity bunching parameter the speckle energy is significant within the spectral interval, where the spectrum of large ocean waves is concentrated. In this case the speckle noise can not be suppressed efficiently by means of image filtering. Meanwhile, the mentioned second item is nothing other than half of the correlation function of the complex intensity, which is the square of the SAR signal complex amplitude (unlike the usual real intensity, i.e. the square of the modulus). Therefore, the unspeckled image correlation function can be presented as the difference between the real intensity correlation function and half of the complex intensity function. This leads to a new spectral estimate, free of speckle noise, for the SAR image. The corresponding expression for the new estimate is presented.

Synthetic Aperture Radar (SAR) signal model is considered as a series of echo signals in range direction. The procedure of Principal Component Analysis (PCA) is introduced which is used as transformation basis to sparsify the SAR signals. The joint Compressive Sensing (CS) and PCA algorithm is derived to realize SAR raw data sparse and compressive measurement. The numerical simulation results demonstrate that the PCA method has good sparse performance and the joint CS and PCA algorithm is possible to online compressive measure the SAR raw data.

It was shown recently that three different types of short‐period internal wave (IW) synthetic aperture radar (SAR) signatures occur on the Iberian Shelf depending on parameters of surface active films. Large‐scale modulation of film characteristics by currents associated with internal tidal waves can also produce a signature in ERS SAR images. On the western Iberian Shelf short‐period IWs typically propagate in groups of packets that are believed to be generated by the evolution of internal tidal waves over the shelf. Here onshore propagating short‐period IWs can exhibit different SAR signatures within the same wave packet according to their position relative to the phase of the internal tidal wave. These transitions of signature mode can be explained by large‐scale variations of film parameters produced by the internal tidal waves. At low‐to‐moderate winds, leading waves in the IW packets usually exhibit double sign signatures, which evolve to negative sign signatures for the subsequent waves in the packets. At very low, near‐threshold winds the IW signatures can be in the form of the double sign type undergoing transition to positive sign signatures when compared to the background behind the IW packet. This is a consequence of different threshold wind speeds for excitation of Bragg waves at different film pressures. An increase of unperturbed film pressure in the direction of the ranking order of solitons in a packet of short‐period IWs, which is predicted by a theoretical model and in agreement with measurements of film elasticity, is demonstrated. Observations of SAR signature mode transitions are concluded to be consistent with previous model results, and a diagram describing mode transitions of the IW signatures in relation to film pressure and wind speed is presented.

With the rapid development of FPGA parallel processing and DSP float-point computing capability, FPGA and DSP play an increasingly important role in the field of high-speed real-time synthetic aperture radar (SAR) signal processing system. In this letter, based on the SAR imaging needs and principles, taking chirp scaling algorithm for example, we design a spaceborne SAR real-time imaging heterogeneous system implemented by FPGA and DSP. The heterogeneous system uses modular thinking, pipeline and parallel processing techniques, which greatly improves the speed and operation precision in SAR imaging. Besides, the SAR imaging system has a good realtime performance, scalability and faulty tolerance and can well meet the needs of spaceborne SAR imaging system. The system needs 19.72s to generate a 4096*4096 pixel image.

Programmable logic offers an alternative solution for the computationally-intensive functions found in digital signal processing (DSP). Programmable logic can provide increased DSP system performance at reduced system cost. Programmable logic combines the flexibility of a general purpose DSP plus the speed, density, and low cost of an ASIC implementation. In some applications, programmable logic replaces the DSP processor entirely. In others, programmable logic works in conjunction with the DSP processor, offloading the computationally-intensive function and freeing the processor for other functions. This paper describes an alternative to traditional, general-purpose DSP processors. Programmable logic can implement functions beyond the capabilities of today's DSP processors. Field programmable gate arrays (FPGAs) or complex programmable logic devices (CPLDs) potentially provide performance increases of an order of magnitude over traditional DSPs with the same flexibility.

Although Synthetic Aperture Radar (SAR) can capture rich land cover information as a most important advanced technique in the field of international earth observation, the application effects still limited significantly. The reason is that the study of SAR imaging processing, SAR image processing and SAR applications are conducted respectively, the integrated study are lacked for parameter selection of SAR imaging processing and SAR image processing and targets identification of SAR application. Focusing on above science problems, the study for phase high fidelity model of high precision interferometric SAR, SAR non-stationary backscattering characteristics and cognition, SAR three-dimensional electromagnetic scattering modeling and its scattering mechanism and SAR multi-parameters optimization information extraction has been conducted. The typical natural distributed targets and man-made targets such as surface deformation, sea ice, building complex and collapsed building are selected, the method and application study oriented to SAR environmental parameters inversion are conduced, the main result and conclusion are as follows: (1) The overall theoretical frames of SAR information integrated processing was proposed; The simulation and ground validation system used to assess the effects of SAR information integrated processing was created; furthermore, the spaceborne SAR imaging algorithm with three steps focusing processing was proposed and realized the multi-modal integrated imaging processing and improved the imaging processing precision. (2) In terms of SAR information integrated processing of natural targets, focusing on phase high fidelity imaging processing of interferometric SAR surface deformation monitoring, an novel spaceborne SAR high fidelity simulation method based on stationary RCS and improved Goldstein SAR interferogram filter based on empirical mode decomposition were proposed. Focusing on multi-parameters optimization processing of sea ice types classification, the multi-channel spaceborne SAR sparse imaging method based on compressive sensing, Kalman filter for removal of scalloping and inter-scan banding in ScanSAR images and SVM sea ice classification method combined with sea ice concentration were proposed. (3) In terms of SAR information integrated processing of man-made targets, focusing on non-stationary backscattering from building complex, mitigation of azimuth ambiguities in spaceborne stripmap SAR iamges using selective restoration, SAR image despeckling by selective 3D filtering of multiple compressive reconstructed images and man-made target detection in urban areas based on a new azimuth stationary extraction method were proposed. Focusing on three-dimensional modeling and fast extraction of collapsed building, H-a-p method used for collapsed building extraction was proposed.

Doppler rate is an important parameter in synthetic aperture radar (SAR) signal processing since it affects the SAR image focusing. This paper addresses the problem of Doppler rate estimation for spotlight SAR focused with the TWO-STEP algorithm and an improved shift-and-correlation (SAC) algorithm based on the Radon transform is proposed. Firstly, the original SAC algorithm is carried out to get the correlation peak line (CPL). Then the slope of the CPL is determined by the Radon transform and the CPL is corrected to be vertical using the obtained slope. Since there is no zero padding, aliasing will occur in the Doppler rate estimation and the ambiguity number is got from the CPL's slope. However, when the ambiguity number splits into two numbers the obtained ambiguity number may be wrong. This special case is analyzed in the paper and a trick is introduced to deal with it. The real spotlight SAR data processing results are provided to validate the effectiveness of the proposed algorithm. (5 pages)

The synthetic aperture radar (SAR) signatures of moving target are the basis of ground moving target indication and imaging (GMTI&Im) in the framework of SAR systems. However, previous studies are mainly based on the 2-D separable SAR processing, and little work has been done to investigate the signatures of moving target after the application of a particular flne resolution SAR image formation algorithm. In this paper, we derive the image spectrum of moving target after two representative flne resolution SAR image formation algorithms, i.e., the range migration algorithm (RMA) and polar format algorithm (PFA), respectively. Based on the spectrum derived, detailed analysis on the SAR signatures of moving target, including the geometric displacement, residual range migration, and defocusing efiect in both the range and azimuth dimensions are performed. The presented work might be helpful when considering a SAR system with the capability of ground moving target indication and imaging (GMTI&Im).

ML based approach for inverting penetration depth of SAR signals over large desert areas

This paper considers an implementation of a real-time signal processor for high resolution SAR (synthetic aperture radar) imaging. In many tasks, we need the SAR imaging take in time, so the real-time processor becomes more and more important. On the basic SAR imaging principle, it is well known that the high range resolution depends on the transmitted signal bandwidth, while high azimuth resolution results from the space Doppler frequency bandwidth. With the increase of frequency bandwidth, the rate of sampling increases, so a fast processor is required in high resolution real-time SAR imaging. To address this need, we discuss the way in which the high speed general DSP and special DSP are applied for high resolution real-time imaging, and good performance is obtained.

• Quantitatively assess penetration and retrieval depths for C- and L-band SAR • Compare penetration depths between compact and full polarizations of SAR. • Compare simulated penetration depth with experiment-derived retrieval depth. • Analyze the effects of incidence angle and vegetation on soil moisture retrieval. • Test six types of polarimetric features for each polarization mode. Soil moisture is critical for various agricultural applications such as crop monitoring and irrigation management. Synthetic Aperture Radar (SAR), especially at L-band and C-band frequencies, has been widely utilized for soil moisture estimation across different polarizations. However, the ambiguity in the depth of soil moisture retrieval remains a challenge due to the complex interactions between SAR signals and ground targets. In this study, the sensitivity of multi-frequency and multi-polarization SAR to soil moisture retrieval at various depths was quantitatively analysed. First, using the Dobson semi-empirical dielectric mixing model, the penetration depth of C-band SAR was found to be limited to the top surface soil (0–5 cm), while L-band SAR could penetrate from 3 cm to more than 20 cm depending on soil properties. Next, the accuracy of soil moisture retrieved at five depths (0–5 cm, 5 cm, 20 cm, 50 cm, and 100 cm) was evaluated using in-situ soil moisture data. Using Random Forest (RF) regression and polarimetric features, the volume scattering of C-band SAR was demonstrated as the dominant scattering mechanism, leading to reduced accuracy across all depths. In contrast, L-band SAR achieved the highest accuracy at the 5 cm depth, constrained by the limited intervals of moisture measurements. Furthermore, the analysis of incidence angle and vegetation coverage revealed that lower incidence angles (15–45 degrees) and lower vegetation conditions improved the accuracy for C-band SAR. L-band SAR, however, exhibited less sensitivity to vegetation coverage when retrieving soil moisture from shallower depths. These findings provide valuable insights for selecting SAR data suitable for soil moisture retrieval in agricultural regions.

Synthetic aperture radar(SAR) imaging processing is a complex operation that requires large amounts of floating point computations. It is very time-consuming to convert SAR raw data into an image on microcomputers. This paper presents a digital imaging matrix algorithm. This algorithm includes range compression, azimuth compression and range walk correction which are implemented by matrix (vector) operation or matrix (vector) translation. It is available for implementation of SAR real-time imaging, and especially suitable for parallel computation on parallel processor, on vector processor. Especially, it provides a new design method for hardware process. The authors design a SQDSPS (SAR Quick-look Digital Signal Processing System) with the algorithm, which is different from the quick-look algorithm SPECAN. The experimental results indicate that the matrix algorithm is significant for saving the SAR imaging time.

Recently many researchers have turned their interests to Orthogonal Frequency Division Multiplexing (OFDM) signal since its promising features in radar. This paper concerns a novel Synthetic Aperture Radar (SAR) system which employs this OFDM signal. Though the OFDM will bring lots of advantages, the performance may be changed since the signal of SAR is different from conventional ones. To evaluate the change, this paper will give a theoretical analysis and the corresponding simulation results from the viewpoint of ambiguity function. This ambiguity function is equivalent to the role of Point Spread Function (PSF) which is often used in SAR for evaluating resolutions. Comparing to the conventional SAR with LFM signal, it is proved that the resolution of SAR based on OFDM is equivalent to the conventional one or even better. This ambiguity function also provides a principle for selecting various OFDM signals as the transmit signal of SAR.