Recent years have seen a surging interest in several novel tools pertaining to SAR, such as multichannel high-resolution and wide-swath (HRWS) SAR, multibaseline interferometric SAR (InSAR), multisubband SAR, polarimetric SAR (PolSAR), and polarimetric SAR interferometry (PolInSAR). We believe that these new approaches to SAR have valuable scientific applications. Here, we present a new experimental airborne SAR system named “N-SAR” (SAR of the Nanjing Research Institute of Electronic Technology) that can fulfill new requirements and is scalable to allow rapid development of modern SARs. As a dual-antenna airborne SAR system, the N-SAR system will be used to test new technologies and signal processing algorithms such as PolSAR and PolInSAR, multibaseline SAR interferometry, multichannel multichannel HRWS SAR/InSAR, and SAR ground moving target indicator. It will play a key role in evaluating the performance of current engineering-oriented SAR systems by using several new operational modes for scientific purposes. In this paper, we provide a conceptual description of the general system design features, instrument design, and capabilities of the N-SAR system. To meet the requirements of different experiments, a novel operational mode, named the alternating bistatic multipolarized mode based on the N-SAR system, is presented. A series of flight tests that started in April 2017 and will be carried out over the next few years are shown. Several preliminary experimental results pertaining to the calibration of PolSAR, multichannel SAR imaging, and interferometry are presented in this paper as an early validation of the capabilities of the N-SAR system.

The great development of high-resolution SAR system gives more opportunities to observe building structures in detail, especially the advanced interferometric SAR (InSAR), which techniques attract more attention on exploiting useful information on urban infrastructures. Considering that the high-rise buildings in urban areas are quite common in big cities, it is of great importance to retrieve the three-dimension (3D) information of the urban high-rise buildings in urban remote sensing applications. In this paper, the 3D reconstruction of high-rise buildings using the wrapped InSAR phase image was studied, referring to the geometric modulation in very high resolution (VHR) SAR images, such as serious layover cause by high-rise buildings. Under the assumption of a rectangular shape, the high-rise buildings were detected and building façades were extracted based on the local frequency analysis of the layover fringe patterns. Then 3D information of buildings were finally extracted according to the detected façade geometry. Except for testing on a small urban area from the TanDEM-X data, the experiment carried on the single-pass InSAR wrapped phase in the wide urban scene, which was collected by the Chinese airborne N-SAR system, also demonstrated the possibility and applicability of the approach.

This article presents a method for extracting the relative polarimetric distortion parameter (PDP) values of polarimetric radar systems, including polarimetric synthetic aperture radar (PolSAR). By using one trihedral and two dihedrals and ignoring the high-order terms of the channel crosstalk, the PDPs of a PolSAR system can be estimated efficiently and straightforwardly without the need for iterative procedures or the system reciprocity assumption. Most importantly, the applicability issues are analyzed to obtain accurate PDP values. A sensitivity analysis of the target orientation angle (TOA, a rotation about the radar line of sight) error $\Delta \bm{\theta }$ is theoretically analyzed and experimentally studied. It appears that the impacts of $\Delta \bm{\theta }$ of different known targets on the channel imbalances and channel crosstalk estimation can be relatively independent and distinguished using our first-order approximate method. Using the proposed method, the channel imbalances are first estimated using the trihedral and 45° dihedral corner reflectors. A 22.5° dihedral should be involved to solve the sign ambiguity. The TOA error of the 45° dihedrals is not significantly sensitive to the channel imbalance estimation. Then, the channel crosstalk can be estimated using the trihedral and 0° dihedral corner reflectors. The channel crosstalk estimation in this step is relatively sensitive to the TOA error, which should be reduced to an acceptable level. Limitations due to the radar cross-section issues of the corner reflectors and the strength of the original channel crosstalk are also analyzed. Finally, the results of simulations and practical N-SAR experiments show the effectiveness of our proposed algorithm.