## 4 Simulation Results and Discussion
### Simulation 2  
In simulation 2, we designed a simulation to detect three sets of ship targets based on the B3I signals of satellite 3 considering Gaussian noise and sea clutter based on the Weibull model. The ship target information and geometric diagram are also expressed in Table 2 and Figure 7.  
In Figures 11 and 12, we show the Doppler compensation effectiveness comparison of the two compensation methods. In Figure 11, we simulated the one-dimensional range detection compensated results of three ship targets without target estimation information, and the results are compensated for with single Doppler channels and the MTDC method. Figure 11a-c show the incomplete peak amplitudes of three ship targets, and Figure 11d shows the target peaks without Doppler phase influence, which shows the effectiveness of MTDC in estimating no-target information situations. Figure 12 shows the compensation results with acquired target estimation information. Figure 12a-c show that each target peak can return to the normal level under the corresponding Doppler compensation and that other target peaks lose part of their amplitudes. Figure 12d shows the MTDC method compensation results expressing all target peaks, obtaining their maximum level. The results of Figures 11 and 12 verify that the proposed MTDC method can remove the Doppler phase influence of multiple target detection. Figure 11: Doppler compensation comparison of method 1 in a one-dimensional range image using B3I signals of satellite 3: (**a**) Results with Doppler channel 1 compensation; (**b**) results with Doppler channel 2 compensation; (**c**) results with Doppler channel 3 compensation; (**d**) results with the proposed MTDC method based on multiple Doppler channels. Based on the same sampling at 33 m, we plotted the one-dimensional range detection results of three ship targets by satellite 3 in Figure 13, where Figure 13a,c,e show the sampling detection results at 3 m and the sampling detection results at 33 m for ships 1, 2, and 3, respectively. Compared with the RCS data of Figure 13b,d,f, we found that the sampling detection at 3 m can express the general outline of the ship's target RCS without accurate amplitude and range point information. The small peaks in the sampling results at 33 m, which are in good agreement with the sampling data obtained at 33 m, express segmented scattering strong points with accurate amplitude and computable range points. The results can be more accurate in the service of target recognition. Figure 12: Doppler compensation comparison of method 2 in a one-dimensional range image by B3I signals of satellite 3: (**a**) results with first target Doppler compensation; (**b**) results with second target Doppler compensation; (**c**) results with third target Doppler compensation; (**d**) results with the proposed MTDC method based on multiple estimated target Dopplers. Figure 13: One-dimensional range detection results of 3 ship targets under the detection of satellite 3 with 33-meter echo sampling and 3-meter echo sampling and the corresponding RCS data distribution: (**a**) ship 1 detection result; (**b**) ship 1 RCS data; (**c**) ship 2 detection result; (**d**) ship 2 RCS data; (**e**) ship 3 detection result; (**f**) ship 3 RCS data. To further study the resolution improvement method, we simulated the detection results of satellite 3 with range inverse methods to acquire the more delicate RCS distribution of targets based on the sampling frequency \(f\)s = 10*B. Figure 14 shows the range inverse results of method 1, in which we screened the probable target information by amplitude and segment; the results are given by a certain length in the low-amplitude region. The dotted line in Figure 14 expresses the RCS data, and the circle line, which is the inverse result, which does not consider clutter, is in good agreement with the data in terms of the amplitude and range point, especially at strong scattering points.