Fig. 1. Frequency modulation waveform of triangular wave

Fig. 2. Echo signals and the corresponding spectrum analysis diagrams. (a) Echo signal without noise; (b) spectrum analysis of noiseless echo signal; (c) echo signal with noise; (d) spectrum analysis of noisy echo signal

Fig. 3. Noisy echo signal and the corresponding spectrum analysis diagram. (a) Echo signal with random noise; (b) spectrum analysis of noisy signal

Fig. 4. Time spectrum diagram of echo signal. (a) STFT; (b) CWT; (c) SST

Fig. 5. Time spectrum diagrams of three algorithms. (a) STFT; (b) CWT; (c) SST

Fig. 6. Comparison of three algorithms for instantaneous frequency identification under different signal-to-noise ratios

Fig. 7. Installation physical diagram

Fig. 8. Time domain waveform of radar echo signal

Fig. 9. Time spectrum diagrams of echo signal. (a) CWT; (b) STFT; (c) SST; (d) SST-median filtering

Fig. 10. Comparison of three inverse transforms

Fig. 11. Comparison of I values at different distances for different transformations