## 6 Simulation Experiments and Results
As a result, the point target is defocused seriously and the image is blurring, shown in Figure 12.  
After the experiment of GTLR-BiSAR sliding spotlight mode, we design the parameters and carry out simulation experiments and data processing of GTLR-BiSAR TOPS mode. The simulation parameters and data processing results are are given directly as follows. Since the processing procedure is similar to the sliding spot mode, the focused and evaluation results are given directly. Similarly, the NLCS method cannot be used in this case. Table 3 describes the experiment parameters of GTLR-BiSAR TOPS mode. Compared with Table 1 the sliding factor is different because of the geometry difference. The focused results are shown in Figure 13 and Table 4. The NLCS result is shown in Figure 14. Moreover, the transmitted bandwidth is much smaller because GTLR-BiSAR TOPS mode  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Range**} & \multicolumn{3}{c}{**Azimuth**} \\ \cline{2-7}
**Target** & **PSLR (dB)** & **ISLR (dB)** & **IRW (m)** & **PSLR (dB)** & **ISLR (dB)** & **IRW (m)** \\ \hline
2 & \(-13.368\) & \(-11.035\) & \(1.499\) & \(-13.116\) & \(-9.711\) & \(0.773\) \\
4 & \(-13.435\) & \(-11.151\) & \(1.499\  
is characterized with large-scale imaging and lower resolution. The resolution is designed as 10 m (azimuth) \(\times\) 10 m (range) theoretically. The 5 \(\times\) 5 point targets are scattered in the illuminated scene area with the size of 80 km (azimuth) \(\times\) 40 km (range). Figure 12: Comparison of imaging results obtained by convention NLCS method and the proposed method. (**a**) The imaging result of NLCS method, considering the azimuth perturbation generated by local fit method. (**b**) The imaging result of our proposed method. \begin{table}
\begin{tabular}{c c c c} \hline \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 & 16 MHz & Sampling Rate & 21.76 MHz \\ Off-nadir Angle & 4.50\({}^{\circ}\) & Off-nadir Angle & 29.03\({}^{\circ}\) \\ Pulse Repetition Frequency & 2000 Hz & Sliding Factor & 2.1639 \\ 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) & 4 m \(\times\) 0.4 m \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Simulation experiment parameters of GTLR-BiSAR TOPS mode. Figure 13: The imaging results of point targets for GTLR-BiSAR TOPS mode. In the practical application of SAR image formulation, there exists parameters measurement errors, such as the velocity error and slant range error. In order to reduce the image defuse, we can integrate some autofocus algorithms [30] with our proposed approach to improve the focusing accuracy. Moreover, we apply the traditional backprojection (BP) method to focus the center target. The result emphasizes the significance of our proposed approach. The PSLR, ISLR and IRW of selected target by time domain method are basically consistent with the frequency method we put forward. However, it takes 3.6798 s to focus a single target, which is an unbearable time consumption for scene imaging. So, we focus our attention on the frequency domain method and apply it in the scene imaging of wide swath.