# Deceptive Jamming Detection for SAR Based on Cross-Track Interferometry
## 1 Introduction  
With its all-day, all weather, long-range, and wide-mapping capabilities, synthetic aperture radar (SAR) has been applied in a wide range of areas [1; 2; 3; 4; 5; 6]. In practice, the SAR system often suffers from complicated electromagnetic interferences. Meanwhile, a variety of jamming techniques, including barrage jamming and deceptive jamming [7; 8; 9], were developed to reduce the effectiveness of SAR. Barrage jamming can degrade the quality of SAR image significantly by raising the noise level, while deceptive jamming introduces some false targets to cover useful information or interfere with the target extraction and tracking algorithms employed in SAR [10; 11; 12]. Generally, deceptive jamming is an effective electronic countermeasure (ECM) technique against the SAR system. The jammer can generate deceptive signals by rapidly estimating the SAR signal parameters, such as carrier frequency, chirp rate, bandwidth, etc. [13; 14], or re-transmit the intercepted SAR signals with different time delays [13; 15]. In recent years, various deceptive jamming methods were proposed. A large scene deceptive jamming method for space-borne SAR is proposed in [16]. An improved method for SAR scattered wave deception jamming, proposed by [PERSON] et al. [17], has been successfully applied for enlarging the jamming area. As an extension, the range difference measuring approach has been successfully utilized for deceptive jamming of squint SAR based on multiple receivers [18]. To protect the SAR system from such attacks, several electronic counter-countermeasure (ECCM) strategies were proposed. In [15], radiometric calibration is utilized to identify false signals through establishing a quantitative relationship between target backscattering and SAR image gray values. After changing the relative RCS of known targets, the jammed area is then discovered by analyzing the pixel gray values ofthe image. However, the speed of SAR imaging is very fast and it is difficult to change the relative RCS of known targets in time. In [19], a detection scheme using dual antennas is proposed, where the false target is detected by cancelling the corresponding pixels in two SAR images with a proper weighting coefficient. However, due to difficulty in deriving the coefficient for each pixel, it is not an easy task to identify the false targets on the scene with hypsography changes [19]. The above methods are based on the statistical characteristics of SAR image pixels, especially the amplitude of false signals. However, when the deception reflectors are not strong or the backscattering characteristics of ground targets are complicated, these methods may become less effective. In [20], the influence of SAR deceptive jamming on the InSAR process is studied and it is found that the property of interferometric phase between real targets and false ones are quite different. Therefore, in this paper, to identify deceptive jamming more effectively, a novel approach is proposed based on cross-track interferometry by exploiting the interferometric phase differences between real targets and false ones in the corresponding SAR images. The proposed method detects deceptive jamming of SAR image with single-pass SAR interferometry. Initially, one antenna serves as a transmitter and two cross-track antennas record the scattered signals simultaneously. Then, the corresponding SAR images are co-registered with each other and the interferogram of the two SAR images are obtained. The real phase, representing terrain features, varies at different positions with the terrain difference, while the false phase approaches a constant value. As a result, the false target can be identified in the interferogram. Finally, the false phase is extracted through frequency detection in the range direction. For more effective extraction, phase filtering is implemented before frequency detection. The paper is organized as follows.