*4.2. Validity Experiment of Reconstruction Algorithm*

With the aim of verifying the validity of SL0 and OMP reconstruction algorithm for the classification of aircraft targets, we conduct an experiment. In this experiment, in order to better simulate the actual work of radar target classification and recognition, the training dataset of 600 single-wave gate complete echo data samples are extracted features which are used to train the SVM model. Several comparative testing experiments are conducted with different testing dataset, two of which take the reconstructed echo data obtained by SL0 and OMP algorithms as the testing dataset, and the results are shown as the blue curve and the black curve, respectively, in Figure 11. As a comparison, we take another complete echo data samples as the testing dataset, and the result of average classification probability is shown as the red curve. In addition, we take the sparse echo data samples as the testing dataset to verify that the sparse echo data worsen aircraft targets classification due to the loss of several echo information elements.

**Figure 11.** Contrast experiment of reconstruction algorithm.

From Figure 11, we can see that the classification probability of sparse echo data is the lowest, which distributes around 33%, and does not vary with the change of SNR. This shows that the sparse echo data loses the components reflecting the micro-Doppler effect of the rotating parts. We can also say that the helicopter, propeller aircraft and jet aircraft cannot be distinguished correctly by extracting the three kinds of features through the sparse echo data. The correct classification probability of the complete echo data is the highest, and with the increase of SNR, the correct classification probability increases gradually and stabilizes at 99.33%. Although the correct classification probability of reconstructed echo data obtained by the SL0 and OMP algorithms is lower than that of complete echo data, it is obviously higher than that of sparse echo data, which verifies the validity of the two kinds of reconstruction algorithms for reconstructing echo data. When the SNR is lower than −12 dB, the classification probability of the reconstructed echo data between the two algorithms is similar. When SNR is higher than −12 dB, the classification effect of the SL0 reconstruction algorithm is better than that of OMP reconstruction algorithm, which is consistent with the reconstructed results of frequency domain echoes of two kinds of algorithms in Section 2.2.
