# Multi-Frequency Target Detection Techniques for DVB-T Based Passive Radar Sensors
## 5 Experimental Results for Aerial Surveillance Application
### Extensive Analysis of the Target Detection Performance  
As an example of the results obtained with the proposed MF integration schemes, Figure 7 reports the output of the application of these schemes against the same dataset considered in Figure 6. Specifically Figure 7a reports the detection results obtained with a decentralized detection scheme based on a 2-out-of-4 strategy (DEC-MF-2/4) which was verified to be a quite robust and effective solution among the possible decentralized strategies. Figure 7b refers to the case of a centralized integration scheme using all the available frequency channels (CEN-MF-4). By comparing Figures 6 and 7, the detection performance improvement provided by the MF approaches is quite apparent as many additional plots are obtained for the targets of opportunity. In the following, we define a given detection as \"correct\" when it appears at the expected range-velocity location at the expected time instant. With this counting procedure, reasonably accurate estimates of the detection rate can be obtained because, when the false alarm rate is kept sufficiently low, it is very unlikely to include false plots within the correct detections. This procedure can be easily implemented based on the availability of accurate enough truth data (temporal interpolation can be performed against time discontinuous data for the air traffic of opportunity). All the remaining plots are then labeled as false alarms. Based on the definitions above the improvement is found to be substantial for the long track appearing at about 220 m/s. In fact, with both the considered MF schemes, the corresponding aircraft is almost continuously detected all along the performed acquisition. Specifically, for that target, the number of correct detections moves from 12 with the worst performing single channel, to 20 using the best performing channel, to 29 with the DEC-MF-2/4, up to 35 when the CEN-MF-4. We recall that the number of possible detections for each target is equal to the available data files within the observed area (in range, velocity and angular sector), namely 44 for the considered target. Moreover the number of false alarms appears to be significantly reduced when jointly exploiting all the available frequency channels according to one of the considered MF strategies. In this regard we recall that, when applying the proposed MF detection schemes, the detection threshold are properly set in order to achieve, after integration, the same nominal false alarm rate provided by the SF operation. By extending the above analysis to all the available data sets, we evaluated the number of correct detections performed against all the targets of opportunity included in the available air-truth. Moreover, the actual false alarm rate has been estimated by averaging over range/velocity areas where no target is expected to fall. Clearly, the number of pixels constituting these areas across the available data files was kept sufficiently high as it sets the confidence interval for the estimation of the false alarm rate. Based on the global number of samples exploited, the margin of error is expected to be in the order of 2.5% for a 0.95 confidence coefficient. The results when separately exploiting the four available frequency channels and after the MF integration schemes including various number of channels are reported in Table 2. Specifically, in the first columns of the table, the number of correct detections are reported for each data set and the bold font is used to highlight the best case identified for each different solution. The penultimate column of Table 2 lists the total number of correct detections summed up across all the available data sets so that it provides an overall analysis in term of target detection performance.