# Small-UAV Radar Imaging System Performance with GPS and CDGPS Based Motion Compensation
## 3 Experimental Results
### Second Test Case
Figures 16b and 17b corroborate that the tomographic images obtained by exploiting CDGPS data are focused images in which the air-soil interface appears flat, as it is actually, and the relative distance among all targets as well as their elevation from the ground are estimated properly. The maximum error is of 0.7 m and regards the estimation of the distance between Target 1 and Targets 2 provided by the tomographic image referred to Track 2. Focused images allowing an approximated localization of the targets are achieved also by using GPS data even if the imaging capabilities are degraded respect to those obtained by using CDGPS (compare Figure 16a,b as well as Figure 17a,b). Indeed, in Figures 16a and 17a the air-soil interface does not appear flat and the errors on the localization of the targets are larger. These degradations are more visible in Figure 16a than in Figure 17a, i.e., for Track 1. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & \multicolumn{2}{c}{**Specification**} \\ \hline Time Gating & Start Time: 25 (ns) & End Time 47 (ns) \\ \hline Frequency range & \(f_{min}=3.1\) (GHz) & \(f_{max}=4.8\) (GHz) \\ \hline Frequency step & \multicolumn{2}{c}{35 (MHz)} \\ \hline Imaging Domain & \(x\)-axis size: 33.76 (m) & dx: 0.025 (m) \\ \cline{2-3}  & \(z\)-axis size: 3.10 (m) & dz: 0.025 (m) \\ \hline TSVD threshold (T) & \multicolumn{2}{c}{\(-12\) (dB)} \\ \hline Subdomain Aperture (L) & \multicolumn{2}{c}{4 (m)} \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Signal Processing Parameters: Track 2. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & \multicolumn{2}{c}{**Specification**} \\ \hline Time Gating & Start Time: 16 (ns) & End Time: 39 (ns) \\ \hline Frequency range & \(f_{min}=3.1\) (GHz) & \(f_{max}=4.8\) (GHz) \\ \hline Frequency step & \multicolumn{2}{c}{25 (MHz)} \\ \hline Imaging Domain & \(x\)-axis size: 27.32 (m) & dx: 0.025 (m) \\ \cline{2-3}  & \(z\)-axis size: 4.37 (m) & dz: 0.025 (m) \\ \hline TSVD threshold (T) & \multicolumn{2}{c}{\(-15\) (dB)} \\ \hline Subdomain Aperture (L) & \multicolumn{2}{c}{4 (m)} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Signal Processing Parameters: Track 1. Figure 15: Test 2-Track 2: (a) raw data; (b) east–north UAV positions estimated by GPS (solid blue line) and CDGPS (solid red line), along-track direction defined by GPS (dashed blue line) and CDGPS (dashed red line); (c) UAV Altitude estimated by GPS (solid blue line) and CDGPS (solid red line), average altitude defined by GPS (dashed blue line) and CDGPS (dashed red line). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & \multicolumn{2}{c}{**Specification**} \\ \hline Time Gating & Start Time: 16 (ns) & End Time: 39 (ns) \\ \hline Frequency range & \(f_{min}=3.1\) (GHz) & \(f_{max}=4.8\) (GHz) \\ \hline Frequency step & \multicolumn{2}{c}{25 (MHz)} \\ \hline Imaging Domain & \(x\)-axis size: 27.32 (m) & dx: 0.025 (m) \\ \cline{2-3}  & \(z\)-axis size: 4.37 (m) & dz: 0.025 (m) \\ \hline TSVD threshold (T) & \multicolumn{2}{c}{\(-15\) (dB)} \\ \hline Subdomain Aperture (L) & \multicolumn{2}{c}{4 (m)} \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Signal Processing Parameters: Track 1. Figure 16: Tomographic images Test 2-Track 1 obtained by Shift and Zoom TSVD algorithm: (**a**) GPS based MoCo; (**b**) CDGPS based MoCo. Figure 17: Tomographic images Test 2-Track 2 obtained by Shift and Zoom TSVD algorithm: (**a**) GPS based MoCo; (**b**) CDGPS based MoCo.