# LEO-Based Satellite Constellation for Moving Target Detection
## 3 Results
### Pre-Compensation Results  
Figure 4 shows the SKT [10] processing results of the LEO-based satellite echo before and after the pre-compensation operation. It can be seen from Figure 4a that there exists obvious range cell migration (RCM) in the original echo. For LEO satellite, the severe Doppler ambiguity issue will lead to the mismatch of SKT compensation function, and the first-order to third-order RCM cannot be removed, as indicated in Figure 4b. While the Doppler ambiguity issue can be solved by implementing the pre-compensation operation. Besides, the range-azimuth coupling problem is correctly handled after SKT process, as demonstrated in Figure 4c. Here, the orbit eccentricity, orbit height, rising intersection right ascension, orbit inclination, perigee angle, perigee time, azimuth and pitch angle of the antenna beam center related to the satellite is set to 0.003, 580 km, 195\({}^{\circ}\), 55\({}^{\circ}\), 200\({}^{\circ}\), 0, 90\({}^{\circ}\) and 30\({}^{\circ}\), respectively. For each satellite, the PRF, carrier frequency and signal bandwidth  
Figure 3: The flow chart of multi-source fusion CFAR detection algorithm.  
are given by 1000 Hz, 9.65 GHz and 50 M. Let the intersection point of the beam center and the earth surface be the coordinate origin, and the moving target coordinate is given by [5 km, 1 km].  
Based on the above pre-compensation operation, the multi-source fusion result in range-DFR domain is shown in Figure 5, where the satellite number is 4, and the parameter setting is consistent with that in the upper paragraph, except that the perigee times of the other three satellites are set as [\(-\)0.5, 0.5, \(-\)1.5]. Here, the perigee time is defined as the moment when a satellite is nearest the earth, around which it turns, and the perigee time in this paper is measured in seconds.  
For the pre-compensation operation, it should be noted that the echoes over the 10 s dwell time are segmented into 5 frames as a result of the complex reflectivity fluctuation, and the complex reflectivity can be regarded as a constant within each frame. That is, coherent accumulation is performed within one frame, and incoherent accumulation is carried out between two adjacent frames.  
Figure 4: SKT processing results before and after the pre-compensation operation. (**a**) The original echo; (**b**) SKT processing results before the pre-compensation operation; (**c**) SKT processing results after the pre-compensation operation.  
To evaluate the theoretical boundary of the pre-compensation operation, Figure 6 shows the unambiguous Doppler interval, as revealed in the yellow area, which is depending on the target velocity vector as well as the range between the cell where the beam center is pointed and that is under test. In ENU coordinate, the included angle of the target velocity direction is set as 45 degrees along the \(x\) axis in clockwise direction. One can see that there exists no Doppler ambiguity issue provided that the target velocity is less than 63 knots, and the range deviation from the cell where the beam center is pointed is within a 80 km radius.