# Improved 2D Ground Target Tracking in GPS-Based Passive Radar Scenarios
## 6 Results with Real Data
### Results
The estimated trajectory is mostly on the road, close to the actual location provided by the GPS data of the cooperative target. The higher estimation deviations are presented in the second part of the trajectory where the target's SNR decreases and detection failures appear. Target detection and localization start when the target trajectory exceeds the PR position and continues for more than 10 s, reaching a maximum detection distance of 98 m from the PR location. System localization capability has also been analysed, taking into account the Euclidean distance between the estimated and the actual location provided by the GPS data of the target. Figure 12(b) shows the estimated localization error for the cooperative target as a function of the CPIs at which the target estimation was available. The localization error remains below 8 m along the entire trajectory, with the highest deviations in the second part of the trajectory where the target detection probability reduces. The average localization error is 2.38 m. Therefore, the combination of GPS-based PR target detection from a single satellite transmitter and the application of beamforming techniques for localization in a local Cartesian space results in high quality localization performance even though the bistatic resolution associated with the selected GPS signal (2 MHz bandwidth) is 150 m.  
Figure 12: Real radar data results: Cumulative detection output in measurement and tracking domain. (a) RDM. (b) Local Cartesian space. Figure 13: Localization results for a cooperative target: (a) Google Earth view of the cooperative target’s estimated position (green) versus target GPS data (purple); (b) Estimated localization error for the cooperative target. Results obtained for both non-cooperative targets are shown in Figure 14. As in the case of the cooperative target, their estimated trajectories mostly fit the road line for their direction of motion (right side of the road away from the PR location). The highest deviations are obtained for the second non-cooperative target, with a maximum error of 12 m from its road line whereas the first non-cooperative target's maximum deviation from its road line is approximately 9m. Targets detection starts once their movement reaches the coverage of the surveillance antennas. In this case, the maximum detected distances are approximately 68 and 55 m from the PR location for the first and second non-cooperative targets, respectively. Because both non-cooperative targets appear at the final part of the acquisition, their associated trajectories are shorter than the cooperative one. The lack of GPS data from these targets does not allow the real estimation of the localization error along their trajectory. A summary of the location statistics (mean \(\mu\) and standard deviation \(\sigma\)) obtained for the estimations in both synthetic and real data are presented in Table 1. The better location results are obtained for the cooperative target on the real radar scenario due to its movement close to the PR location. The location error is highly dependent on PR to target distance giving rise to worse location performances for simulated targets far from PR location. Nevertheless, system performances in overall studied cases confirm the applicability of the proposed processing scheme. The assumption of a known target altitude limits the use of the proposed processing scheme to maritime and terrestrial targets. The reflectivity of maritime targets is usually higher, which allows the detection at higher distances. Since the localization error depends directly on the target's range when only the DoA information is exploited, the absolute error in target localization is expected to be larger. To address both the increase of localization errors with target distance and the position of airborne targets, future works will study solutions based on multi-static configurations exploiting several line-of-sight GPS transmitters.