LuTan-1 (LT-1) is the first Chinese civilian synthetic aperture radar (SAR) satellite mission dedicated for interferometry. The mission is composed of a constellation of two identical satellites, each carrying an advanced L-band fullpolarimetric SAR. Equipped with both bistatic and mono-static capabilities, LT-1 is designed to generate high-resolution digital elevation model and deformation products for resource and disaster monitoring purposes. Here we provide an overview of LT-1’s satellite and its SAR system, describe the technical challenges that occurred during the development such as the noninterrupted phase synchronization, range ambiguity suppression with hybrid compact polarization and the non-linear frequency modulation waveform. Then we present the data processing pipeline, calibration, and validation reports collected since its launch in early 2022, together with results of several selected applications and experimental modes such as hybrid compact polarization.

The innovative bistatic synthetic aperture radar (BiSAR) mission LuTan-1 (LT-1) employs a non-interrupted synchronization scheme to achieve high-precision phase synchronization. While radio frequency interference (RFI) is a major factor in deteriorating phase synchronization performance. To present the effect of RFI on the synchronization phase clearly, the characteristics of RFI in the synchronization link are described in detail, and a precise analytic expression between the amplitude, frequency, and phase of RFI and synchronization phase error is established. Furthermore, a novel pulse compression-based notch (PCN) method is proposed to eliminate the phase error introduced by RFI. In the proposed method, the saturated distortion signals resulting from strong interferences are detected and discarded by the distribution features of their modes. Then, inspired by contrary thinking, the synchronization signal after pulse compression is notched instead of the RFI. A fast missing-data iterative adaptive approach (Fast MIAA) is performed to recover the gaped RFI signal and remove it from the compressed signal. Finally, the correct synchronization phases can be extracted from the peak positions of the remaining signals. Experimental results derived from using simulated and real synchronization data of the LT-1 system validate the performance of the proposed RFI mitigation method.

The bistatic synthetic aperture radar (BiSAR) plays an important role in remote sensing. However, the deviation between the two oscillators in BiSAR systems will cause a residual modulation of the echo signal. Therefore, the phase synchronization is an important issue that must be addressed in the BiSAR system. An advanced noninterrupted phase synchronization scheme is used for LuTan-1. The synchronization pulses are exchanged immediately after the ending time of the radar echo receiving window and before the starting time of the next pulse repetition interval, which will not interrupt the normal SAR operation. In order to evaluate the accuracy of the phase synchronization scheme, the model of phase synchronization is introduced at first. The hardware design and processing flow of LuTan-1 are introduced in detail. An innovative internal calibration strategy is also described. Then, the test data acquired by the ground validation system are analyzed to verify the effectiveness of the phase synchronization scheme. The signal-to-noise ratio (SNR) and the synchronization rate are the two most important factors to influence the accuracy in phase synchronization. The conclusions have guiding significance for the synchronization module design of LuTan-1 and the future BiSAR system.

The phase synchronization is one of the key issues to be addressed for the bistatic synthetic aperture radar system. In this paper, an advanced non-interrupted phase synchronization scheme is proposed. Both satellites are equipped with four synchronization antennas for a mutual exchange of synchronization pulses, which are transmitted rightly after the radar signal transmitting and before the echo receiving. Therefore, it can not interrupt the normal SAR data acquisition, which can further improve synchronization accuracy and avoid the data missing effect. The ground validation system for TwinSAR-L synchronization module is described in detail. The results are also evaluated to demonstrate feasibility of the proposed scheme.

With the growing scarcity of spectrum resources, frequency sharing among different systems is becoming quite common, which causes radio frequency interference (RFI) to normal synthetic aperture radar (SAR) applications. Recently, in the RFI suppression field, algorithms based on the low-rank property (LRP) assumption have become a popular research topic. However, this assumption is not valid in complicated cases, especially when there are a wide variety of RFIs. To address this problem, in this article, factors that affect the LRP are studied through theoretical analysis and simulation verification, a general RFI model is established to fit complicated cases, and an advanced RFI suppression scheme based on LRP restoration (LRPR) is proposed. The LRPR scheme has three steps. The first step is RFI localization, which captures the rough profile of the RFI in the time–frequency domain for RFI spectrum separation and extraction. The second step is RFI clustering, in which a novel similarity evaluation metric and corresponding two-step clustering algorithm are designed. The final step is RFI suppression. Operations for LRP recovery in each RFI group are proposed, and consequently, classical low-rank approximation methods are applied for RFI suppression. The simulation results for various types of RFI show the robustness and performance improvement of the proposed scheme. In addition, in LuTan-1 data processing, the proposed scheme outperforms classical algorithms in both intensity image recovery and phase preservation.