Huaping Xu

EXTENDED WAVENUMBER DOMAIN ALGORITHM FOR HIGHLY SQUINTED SLIDING SPOTLIGHT SAR DATA PROCESSING

Image formation from squinted sliding spotlight synthetic aperture radar (SAR) is limited by azimuth spectral folding and severe two dimension coupling. This paper presents an Extended Wavenumber Domain Algorithm (WDA) for highly squinted sliding spotlight SAR data processing. This algorithm adopts azimuth deramping approach to overcome the azimuth spectral folding phenomenon. The chirp rate for azimuth deramping and the principle of choosing pulse repetition frequency (PRF) is presented to accommodate the characteristic of Doppler history. Subsequently, the full focusing is implemented by WDA. Instead of the conventional Stolt mapping in WDA, a modifled Stolt mapping is introduced in order to enlarge the range extension of focused image and enable to update the Doppler parameters along range. To conflrm the correctness of the implementation of modifled Stolt mapping and the azimuth position of target in focused image, related compensation terms are developed. Point target simulation results are presented to validate the efiectiveness of extended WDA to process highly squinted sliding spotlight SAR data.

A Novel Non-Interpolation Polar Format Algorithm Using Non-Lineal Flight Trajectories and Auto-Adaptive Prf Technique

The classical interpolation-based Polar Format Algorithm (PFA) for spotlight synthetic aperture radar (SAR) results in numerous computation load, which, reduces processing speed and increase system complexity. To decrease computation load, this paper proposes a novel non-interpolation PFA algorithm for sensor ∞ying along non-lineal ∞ight trajectories, which are specially designed curves in conical surface. Then an innovative auto-adaptive Pulse Repetition Frequency (PRF) technique is put forward to uniformly sample signal in azimuth direction. The computation load of the new PFA is merely left to azimuth chirp z-transforms (CZTs) and range fast Fourier transforms (FFTs) after dechirp processing and residual video phase (RVP) compensation. Two ∞ight modes (ellipse trajectory mode and hyperbola trajectory mode) are analyzed. A lineal approximation method is proposed to simplify non-lineal sensor trajectory analysis. Computer simulation results for multiple point targets validate the presented approach. Comparison of computation load between this PFA and traditional PFA is represented in Appendix B.

SAR ATR based on dividing CNN into CAE and SNN

As for the problem of too long training time of convolution neural network (CNN), this paper proposes a fast training method for CNN in SAR automatic target recognition (ATR). The CNN is divided into two parts: one that contains all the convolution layers and sub-sampling layers is considered as convolutional auto-encoder (CAE) for unsupervised training to extract high-level features; the other that contains fully connected layers is regarded as shallow neural network (SNN) to work as a classifier. The experiment based on MSATR database shows that the proposed method can tremendously reduce the training time with little loss of recognition rate.

A new trajectory-based Polar Format Algorithm for bistatic SAR

The interpolation-based Polar Format Algorithm (PFA) can be used in bistatic Synthetic Aperture Radar (SAR) image processing while suffering from heavy interpolation computation load and complicated space-dependent resolution. To decrease computation load, this paper presents a nonlinear trajectory-based PFA, in which sensors are designed to fly on conical surface to avoid range interpolation. Due to this conical bistatic geometry, two advantages can be achieved. First, part of computation load can be converted to navigation system and processing speed can be improved. Second, a space-independent range resolution can be approached. A following multi-scatter simulation validates the presented approach.

Spaceborne D-InSAR system: Conceptual overview

Spaceborne D-InSAR system is a kind of SAR satellite system aiming at differential interferometry application. It provides us a capability of measuring subtle deformation on the ground with phase difference. Different from existing satellite SAR missions, during the system conceptual design period, the primary objectives is improving the deformation measurement accuracy of the system. This paper is an overall conceptual description of the system, which paves the way for future research works. First of all, the system performance analysis is the key point as a theoretical foundation. The mathematical analysis model should have two typical characters. On one hand, various practical engineering errors in SAR satellite system need to be considered in mathematical modeling work. On the other hand, how to balance conventional 2/3-pass D-InSAR mode with time-series Persistent Scatterer D-InSAR mode is a big challenge. When we finish the model, experimental verification is also needed. Secondly, the satellite constellation configuration has to be designed to evaluate the system observation capability. Of course, we have to sort out the potential industry applications of the system in all kinds of modes that the system can achieve.

Interferometric baseline design and performance evaluation for 3-dimensional formation flying SAR satellites system

The orbital elements determination method for 3-demensional Formation-flying SAR satellites system is developed, basing on the closed form solution to the free orbit movements acquired from Keplers equation. The quantificational relationship between the interferometric baseline, the orbital elements and formation configuration parameters is induced. The general baseline design approach is proposed, basing on the analysis of critical space baseline and critical time baseline. Typical configurations are selected for the L-band FF-SAR satellite systems, including circular configuration, circular horizontal projection configuration and linear horizontal projection. The efficiency of the baseline design technique is validated by the computer simulation results with measurement accuracy of terrain height and velocity.

A new concept: critical number of looks for multilook processing method for InSAR noise suppression

Interferometric synthetic aperture radar(InSAR) is usually employed to provide altitude information of terrain. There are many factors to cause interferogram noise and the noise decreases height measurement accuracy of InSAR. In this paper, Multilook processing technique, which is used to reduce interferogram noise in InSAR, is studied. And a new concept - critical number of looks for multilook processing is proposed. The number of looks must be smaller than critical number of looks when multilook processing is applied to the interferogram noise suppression. The new concept benefits the multilook processing for InSAR noise suppression. With the knowledge of critical number of looks, the proper number of looks can be chosen for InSAR multilook processing to reduce the interferogram noise. The equations of range and azimuth critical numbers of looks are presented for both single baseline spaceborne InSAR and multibaseline spaceborne InSAR. The critical number of looks can be obtained from these equations. In the end, multilook processing with different numbers of looks is applied to InSAR simulated data and the results show the validity of critical number of looks in InSAR.

The influence of system parameters on multibaseline InSAR for layover solution

The Multi-baseline synthetic aperture radar interferometry (InSAR) is capable of solving layover phenomena because of its resolving capability along the elevation dimension. Using baseline diversity of a multi-baseline InSAR system to overcome layover is essentially a matter of spectral estimation problem. The spectrums period and the estimation resolution are influenced by the InSAR system parameters. This paper presents a thorough analysis of the influence of system parameters on the unambiguous height difference and the resolution of height retrieval of layover scenarios. The largest unambiguous height difference is derived and it is related to the baseline number and length. The resolution of height retrieval is determined by the signal-to-noise ratio, baseline number and multilook number. At the end, some useful advices on designing multi-baseline InSAR system parameters are presented.

Spaceborne D-InSAR system: Coherence analysis

Spaceborne D-InSAR system is a kind of SAR satellite system aiming at differential interferometry application. It provides us a capability of measuring subtle deformation on the ground with phase difference. In this work, we focused on the system performance analysis theory as a first step to launch the research work on the overall spaceborne D-InSAR system. After the theoretical model and major error analysis work, we realized that coherence is really important. The qualitative and quantitative analysis showed that the situation becomes worse due to volumetric and temporal decorrelations compared with single-pass InSAR system such as TanDEM-X system. The in-orbit SAR satellite data experiment study validated the quantitative analysis. In order to obtain high-precision D-InSAR measurement, there are some new problems to solve rather than just using an existing SAR satellite to implement D-InSAR.

A scanning order design method of jumping spotlight SAR to simplify imaging processing

Spotlight synthetic aperture radar (SAR) can obtain high resolution SAR image but the observation area is restricted. This paper presents a new imaging mode named jumping spotlight SAR to achieve high resolution and wide swath simultaneously. In jumping spotlight mode, high resolution SAR image is acquired by antenna beams steering, and meanwhile the wide observation swath is realized through antenna beams scanning in range and azimuth directions. The imaging theory of jumping spotlight SAR is given based on the data acquisition geometry and some of the imaging difficulties are analyzed. Then the design principle of the antenna beams scanning order is proposed in this imaging mode. Simulation results show that the scanning order design rule can simplify the processing of squint spotlight imaging.