Hong-cheng Zeng

A Novel General Imaging Formation Algorithm for GNSS-Based Bistatic SAR.

Global Navigation Satellite System (GNSS)-based bistatic Synthetic Aperture Radar (SAR) recently plays a more and more significant role in remote sensing applications for its low-cost and real-time global coverage capability. In this paper, a general imaging formation algorithm was proposed for accurately and efficiently focusing GNSS-based bistatic SAR data, which avoids the interpolation processing in traditional back projection algorithms (BPAs). A two-dimensional point target spectrum model was firstly presented, and the bulk range cell migration correction (RCMC) was consequently derived for reducing range cell migration (RCM) and coarse focusing. As the bulk RCMC seriously changes the range history of the radar signal, a modified and much more efficient hybrid correlation operation was introduced for compensating residual phase errors. Simulation results were presented based on a general geometric topology with non-parallel trajectories and unequal velocities for both transmitter and receiver platforms, showing a satisfactory performance by the proposed method.

Modified Omega-k Algorithm for High-Speed Platform Highly-Squint Staggered SAR Based on Azimuth Non-Uniform Interpolation

In this work, the staggered SAR technique is employed for high-speed platform highly-squint SAR by varying the pulse repetition interval (PRI) as a linear function of range-walk. To focus the staggered SAR data more efficiently, a low-complexity modified Omega-k algorithm is proposed based on a novel method for optimal azimuth non-uniform interpolation, avoiding zero padding in range direction for recovering range cell migration (RCM) and saving in both data storage and computational load. An approximate model on continuous PRI variation with respect to sliding receive-window is employed in the proposed algorithm, leaving a residual phase error only due to the effect of a time-varying Doppler phase caused by staggered SAR. Then, azimuth non-uniform interpolation (ANI) at baseband is carried out to compensate the azimuth non-uniform sampling (ANS) effect resulting from continuous PRI variation, which is further followed by the modified Omega-k algorithm. The proposed algorithm has a significantly lower computational complexity, but with an equally effective imaging performance, as shown in our simulation results.

Fast image-formation algorithm for ultrahigh-resolution airborne squint spotlight synthetic aperture radar based on adaptive sliding receive-window technique

Abstract Adaptive sliding receive-window (ASRW) technique was usually introduced in airborne squint synthetic aperture radar (SAR) systems. Airborne squint spotlight SAR varies its receive-window starting time pulse-by-pulse as a function of range-walk, namely, the linear term of range cell migration (RCM). As a result, a huge data volume of the highly squint spotlight SAR echo signal can be significantly reduced. Because the ASRW technique changes the echo-receive starting time and Doppler history, the conventional image algorithm cannot be employed to directly focus airborne squint spotlight ASRW-SAR data. Therefore, a fast image-formation algorithm, based on the principle of the wave number domain algorithm (WDA) and azimuth deramping processing, was proposed for accurately and efficiently focusing the squint spotlight ASRW-SAR data. Azimuth deramping preprocessing was implemented for eliminating azimuth spectrum aliasing. Moreover, bulk compression and modified Stolt mapping were utilized for high-precision focusing. Additionally, geometric correction was employed for compensating the image distortion resulting from the ASRW technique. The proposed algorithm was verified by evaluating the image performance of point targets in different squint angles. In addition, a detailed analysis of computation loads in the appendix indicates that the processing efficiency can be greatly improved, e.g., the processing efficiency could be improved by 17 times in the 70-deg squint angle by applying the proposed image algorithm to the squint spotlight ASRW-SAR data.

Image formation algorithm for highly-squint strip-map SAR onboard high-speed platform using continuous PRF variation

In highly-squint strip-map Synthetic Aperture Radar (SAR) onboard high-speed platform, the large range-walk is eliminated by continuously varying its pulse repetition interval (PRF), which overcomes the limitation of echo data collection. However, the accompanying problems of azimuth non-uniform sampling (ANS) and changing of Doppler history are inevitable. Therefore, an imaging formation algorithm for this SAR data imagery is proposed firstly. In the proposed algorithm, the range cell migration correction is performed to eliminate the changing of Doppler history. And the baseband Lagrange interpolation is implemented to reconstruct the ANS data. Then, the bulk compression function and stolt interpolation relationship are deduced in the focusing processing. Finally, the imaging results justify the validity and accuracy of the proposed algorithm.

A refined Omega-K algorithm for focusing highly squint airborne stripmap SAR data

The squint synthetic aperture radar (SAR) is capable of improving the coverage performance of SAR system while suffering from large range cell migration (RCM) and heavy computation load. To alleviate RCM, this paper proposes an innovative sliding receive-window (SRW) technique, in which the receive-window starting time varies pulse by pulse as a function of range-walk. Moreover, a refined Omega-K algorithm is deduced for focusing highly squint airborne stripmap SAR using SRW technique. In refined Omega-K, a new stolt interpolation relationship is found for the RCM is modified by the SRW technique. Finally, the imaging results justify the validity and accuracy of the refined Omega-K algorithm.

2-D coherent integration processing and detecting of aircrafts using GNSS-based passive radar

Long time coherent integration is a vital method for improving the detection ability of global navigation satellite system (GNSS)-based passive radar, because the GNSS signal is not radar-designed and its power level is very low. For aircraft detection, the large range cell migration (RCM) and Doppler frequency migration (DFM) will seriously affect the coherent processing of azimuth signals, and the traditional range match filter will also be mismatched due to the Doppler-intolerant characteristic of GNSS signals. Accordingly, the energy loss of 2-dimensional (2-D) coherent processing is inevitable in traditional methods. In this paper, a novel 2-D coherent integration processing and algorithm for aircraft target detection is proposed. For azimuth processing, a modified Radon Fourier Transform (RFT) with range-walk removal and Doppler rate estimation is performed. In respect to range compression, a modified matched filter with a shifting Doppler is applied. As a result, the signal will be accurately focused in the range-Doppler domain, and a sufficiently high SNR can be obtained for aircraft detection with a moving target detector. Numerical simulations demonstrate that the range-Doppler parameters of an aircraft target can be obtained, and the position and velocity of the aircraft can be estimated accurately by multiple observation geometries due to abundant GNSS resources. The experimental results also illustrate that the blind Doppler sidelobe is suppressed effectively and the proposed algorithm has a good performance even in the presence of Doppler ambiguity.

Mutual information upper bond of compressed data using block adaptive quantization algorithm

Block adaptive quantization (BAQ) is widely utilized for reducing downlink data rate of spaceborne synthetic aperture radar (SAR). The mutual information upper bond of BAQ compressed data is proposed by means of establishing a mathematical mapping relationship between output signal entropy and input signal saturation degree, using information theoretical analysis method. Threshold saturation degree of input signal for BAQ to be effective are also obtained. Simulation SAR raw data are used to verify the correctness of the mapping relationship.

The impact of block adaptive quantization algorithm on power-loss with SAR raw data

In order to improve the radiometric precision of Synthetic Aperture Radar (SAR) image, this paper analyses the power-loss of SAR raw data which is caused by block adaptive quantization (BAQ) and then proposed a compensation method. Firstly, the saturation factor γclip is defined and then a unified model of BAQ compression is proposed by using the concept of normalized quantizer. Secondly, the signal expression during BAQ procedure is deduced under the unified model and some important parameters are expressed as a function of γclip. Thirdly, a one-to-one relationship between saturation degree and power-loss of compressed data is established through γclip, the corresponding compensation method is proposed as well. Experiment results based on simulated data prove the correctness of theoretical relationship and the validity of the compensation method.

Modified reconstruction method of squinted multi-channel SAR sigal

Squinted multi-channel SAR is a available mode to achieve the high-resolution and wide-swath, because it is more flexible than broadside SAR. However, the traditional processing algorithm of broadside multi-channel mode is not suitable for squinted multi-channel mode, because the high squint angle will lead the reconstruction to fail. In this paper, a modified reconstruction method adapted to squinted multichannel SAR signal is proposed. The large central Doppler frequency of the squinted Doppler spectrum is taking into account, and the reconstruction method is modified accordingly. Meanwhile, the range walk correction is performed before the reconstruction to remove the mismatch between the reconstruction filters and the squinted signal with large range cell migration. Furthermore, the processing algorithm based on the wave-number algorithm framework with range walk correction is proposed. Finally, computer simulation results are presented to demonstrate the validity of the proposed algorithm.

Data-based onboard estimation of antenna phase center spacing in space-borne azimuth multi-channel SAR system

In space-borne azimuth multi-channel SAR, the antenna phase center spacing should be measured precisely to obtain the reconstruction filters. In this paper, a data-based onboard estimation method of antenna phase center spacing in spaceborne multi-channel SAR system is proposed. Firstly, the principle of data-based onboard estimation is presented, then the estimation method in details is described step-by-step. Finally, simulations are carried out, with two influence factors, SCR and focusing accuracy, to demonstrate the validity of the proposed estimation method.