## 1 Introduction  
Spaceborne SAR-GMTI systems combine high-resolution SAR (synthetic aperture radar) imaging with the GMTI (ground moving target indication) technique to observe the stationary scene and detect moving targets on the ground. In addition to the large coverage of the spaceborne SAR sensor, its day-and-night and all-weather capabilities make it a very interesting tool for traffic management, detection of ground slowly moving targets for military use, and other uses. The planned single-pass distributed spaceborne SAR [1] can provide large and flexible along-track baselines to enhance clutter cancellation performance and decrease the minimum detectable velocity (MDV) for GMTI. However, due to high satellite velocity and the long range between satellites and the earth, suppression of clutter and detection of ground slowly moving targets become a difficult task for spaceborne SAR. The distributed spaceborne SAR-GMTI systems, multibaseline/multichannel ATI (along track interferometry)/DPCA (displaced phase center antenna), and adaptive clutter suppression techniques applied to the SAR image or Doppler domain are always exploited as clutter cancellation techniques [2, 3, 4, 5]. Based on the short/long multiple baselines, the high-resolution SAR satellites TerraSAR-X (TSX) and TanDEM-X (TDX) utilized the bistatic SAR-ATI technique to get highly accurate velocity estimates for slow and fast target movement [6, 7]. In [8, 9], the joint pixel eigendecomposition method is proposed to resolve the SAR image misregistration in the linear clutter suppression scheme for distributed spaceborne SAR-GMTI. In [10], based on the multi-channel SAR images, a radial velocity estimation algorithm is proposed to mitigate the effect of heterogeneous clutter using the joint-pixel normalized sample covariance matrix and the shift vector. [PERSON] and [PERSON] et al. [11; 12; 13; 14] integrated a priori information into the SAR-ATI technique for traffic monitoring with TSX. In reality, except for some special military applications of GMTI, a large majority of targets may travel strictly on roads or highways in a specific direction and within a velocity range. The integration of a priori information into SAR-GMTI was suited for theoretical and engineering applications. In [15], the optimum linear clutter filter integrated with a priori information applied to spaceborne dual-channel SAR-GMTI is proposed, which maximizes the output signal-to-clutter plus noise ratio(SCNR). [PERSON]. [PERSON] et al. [16; 17; 18] proposed an a priori knowledge-based ground moving target indication and parameter estimation algorithm applicable to single as well as to multichannel synthetic aperture airborne radars. In [19], for a multichannel SAR-GMTI system, the along-track baseline is derived based on the subspace projection, where the target radial velocity is estimated according to the azimuth position offset by exploiting the road-aided information. [PERSON] et al. [20] determined that it is difficult to use the road map as a priori information for the dense road network, but the prior road information can be used to assess the GMTI performance. [PERSON] et al. [21] proposed a GLRT detection method to detect the moving targets for multichannel SAR. In [22; 23], a robust optimum adaptive clutter suppression technique for SAR-GMTI applied to the distributed spaceborne SAR, which includes the diagonal loading technique with a priori information integrated into the processor. Research in the area of moving targets detection in the presence of clutter has resulted in a number of adaptive detection algorithms. In general, the generalized likelihood ratio test (GLRT) is always exploited for moving target detection for multistatic or multi-channel SAR-GMTI techniques [15; 21; 22; 23]. Traditional detectors can suppress clutter and achieve detection. In reality, AMF and ABORT are the two well-known adaptive techniques for radar target detection.