## 6 Simulation Experiments and Results  
In this section, we will introduce the simulation conditions and experiment results to validate our proposed algorithm. Taking the GTLR-BiSAR sliding spotlight mode as an example, we will elaborate on the entire simulation experiment and processing details, shown as Figure 10.  
Table 1 describes the experiment parameters of GEO and LEO satellites. The satellite orbit data are generated by satellite tool kit (STK) software and the orbit data are interpolated according to pulse repetition interval (PRI). The parameters of GEO transmitter and LEO receiver are also listed, which are designed according to the desired resolution. The illuminated scene size is determined by the antenna main lobes of GEO and LEO antennas. The point targets are geolocated as shown in Figure 4. Based on the simulation parameters above, we give the results of simulation and processing and make appropriate analysis. Figure 9: The flow-process diagram of the entire process. The typical imaging performance indexes of the targets focused by the proposed method are shown in Figure 11 and Table 2. It is worth noting that the range resolution is related to the bandwidth of the transmitted signal. In order to reduce the amount of simulation data, the resolution is designed as 0.8 m (azimuth) \(\times\) 1.5 m (range) theoretically. The point targets of GTLR-BiSAR system operating in sliding spotlight mode is shown in Figure 4. The \(5\times 5\) point targets are scattered in the illuminated scene area with the size of 5 km (azimuth) \(\times\) 5 km (range). \begin{table}
\begin{tabular}{c c c c} \hline
**Parameters of GEO Transmitter** & **Value** & **Parameters of LEO Receiver** & **Value** \\ \hline Semi-major Axis & 42,166.30 km & Semi-major Axis & 6894.14 km \\ Inclination & 0\({}^{\circ}\) & Inclination & 97.31\({}^{\circ}\) \\ Eccentricity & 0 & Eccentricity & 0 \\ Transmitted Frequency & 9.60 GHz & Received Frequency & 9.60 GHz \\ Transmitted Bandwidth & 100 MHz & Sampling Rate & 120 MHz \\ Off-nadir Angle & 4.50\({}^{\circ}\) & Off-nadir Angle & 29.03\({}^{\circ}\) \\ Pulse Repetition Frequency & 2000 Hz & Sliding Factor & 0.17311 \\ Transmitter Altitude & 35,788.10 km & Receiver Altitude & 515.00 km \\ Transmitter Velocity & 0.23 m/s & Receiver Velocity & 7680.16 m/s \\ Antenna Size (Azimuth \(\times\) Range) & 20 m \(\times\) 6 m & Antenna Size (Azimuth \(\times\) Range) & 5 m \(\times\) 1 m \\ \hline \end{tabular}
\end{table} 
Table 1: Simulation experiment parameters of GTLR-BiSAR sliding spot mode. Figure 10: Simulation data processing. (**a**) The range-Doppler data is aliasing because the PRF is far less than the bandwidth of the received signal. (**b**) After the azimuth deramping pre-processing, the aliasing problem is removed and the efficient range-Doppler algorithm works. (**c**) The range compression is performed. (**d**) After the range compression, we zoom in the target area, the azimuth and range variance can be seen clearly. (**e**) Through azimuth variance analysis and correction, the targets with the same \(R_{r0}\) are confined in the same range migration curve. (**f**) Through range variance analysis and correction, the bulk RCM correction is performed and the spectrum of the targets become straight lines. In addition, the convention NLCS method is utilized to complete the imaging operation. We take the scene center point, i.e., the point target 13 as an example, then we compare the imaging results of the convention NLCS method and the proposed method. The comparison results show that the NLCS method cannot be applied in the GTLR-BiSAR sliding spotlight case, because the signal is azimuth aliasing in time domain after the azimuth deramping pre-processing in Section 3, while the NLCS method is suitable for the case that the signal is not aliasing in both time and frequency domain.