# Feasibility, Design, and Deployment Requirements of TCR for Bistatic SAR radiometric Calibration
## 5 Simulation Experiments  
One basic purpose of radiometric calibration is to obtain the absolute calibration constant, which is the corresponding relation between the target RCS and its pixel value in a SAR image. Therefore, either the accurate RCS or accurate pixel value is critical to calibration accuracy. We have described the theoretical requirements, bistatic RCS characteristics, and error factors of the TCR RCS with electromagnetic simulations. In this section, based on the electromagnetic simulation results, bistatic  
Figure 12: The effect of pointing deviation on the RCS at different bistatic angles. (**a**) Azimuth pointing deviations and corresponding RCS errors; (**b**) elevation pointing deviations and corresponding RCS errors. SAR imaging simulation experiments were conducted to analyze the bistatic image quality and the point target energy, and these were compared with several typical bistatic angles as the TCR boresight is considered or not. The bistatic SAR imaging system parameters are shown in Table 1 and the imaging algorithm is the Range-Doppler (RD) algorithm. The SAR image quality of a point target is a precondition that determines whether to use this target as a calibration target or not. The most common image quality parameters for SAR images are the shape of the impulse response function (IRF). As for a point target, the IRF takes the form of a Dirac delta function, and the image quality parameters of the point target are shown in Figure 13.  
The most important image quality parameters of the point target include [28]: (1) impulse response width (IRW); (2) peak side lode ratio (PSLR); and (3) integral side lobe ratio (ISLR). These features are often considered sufficient to judge the quality of the impulse response performance. The IRW refers to the 3-dB width of the main lode, which is also known as image resolution. The PSLR and ISLR are related to the image contrast. PSLR is the ratio of the highest side lobe power to the peak of the response, and the PSLR is usually less than \(-13\) dB. ISLR is the ratio of the energy contained in the side lobe to the energy contained in the main lobe of the impulse response, and the ISLR is usually about \(-10\) dB. The point target accounts for only one or two pixels in the SAR images. Generally, the upsampling operation is a necessary pre-processing step in order to measure the above parameters accurately. The integral method is commonly used to obtain the absolute calibration constant by measuring the response of the targets. The integrated point target energy is mainly obtained by the difference between the energy of the point target in the integration area and the energy of the adjacent same background area. Typically, the region centered on the peak point is used to describe the target, which includes the target region and the background region [23]. \[E_{cr}=E_{n}-\left(\frac{N_{cr}}{N_{clt}}\right)\cdot E_{clt} \tag{10}\] \begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Data Parameters** \\ \hline Frequency & 9.6 GHz (X-Band) \\ Bandwidth & 100 MHz \\ Pulse width & 1.5 μs \\ Altitude & \(2\times 10^{4}\) m \\ Velocity & 150 m/s \\ Antenna azimuth beamwidth & 0.5\({}^{\circ}\) \\ Azimuth sampling rate & 300 Hz \\ Range sampling rate & 120 MHz \\ \hline \hline \end{tabular}
\end{table} 
Table 1: System parameters used in the simulation dataset. Figure 13: The image quality analysis parameters of the point target. where \(E_{n}\) is the summed energy in the target region, \(E_{clt}\) is the energy in the background region, \(N_{cr}\) is the number of the samples in the target region, and \(N_{clt}\) is the number of samples in the background region. In the following simulation experiments, the bistatic scattering data, containing amplitude and phase information, obtained by electromagnetic simulations were used in the SAR echo simulation and imaging processing, and then the image quality parameters and point target energy were analyzed.