Fig. 1. Relationship between frequency and time in T-FMCW.

Fig. 2. Block diagram with I/Q receiver.

Fig. 3. Workflow of the proposed method.

Fig. 4. Processing results of the proposed method. (a) Iterative process of the frequency peak intensity of long-pulse echo signal; (b) frequency spectrum of the long-pulse echo signal with coherent degradation comparison before and after the proposed method.

Fig. 5. Results of intrapulse coherence degradation suppression method for long-pulse echo signal with different random phase matching frequencies.

Fig. 6. Field verification experiment scheme.

Fig. 7. Optical transceiver and target scenario in the field verification experiment.

Fig. 8. Real target scenario at a distance of 4.2 km from the coherent lidar.

Fig. 9. Frequency spectrum and related results for the target at about 4.2 km. (a) Processing result of long-pulse echo signal with coherent degradation by the proposed method under different random phase-matching frequencies; (b) comparison of the frequency spectrum before and after being processed by this method.

Fig. 10. Real target scenario at a distance of 19.8 km from the coherent lidar.

Fig. 11. Frequency spectrum and related results for the target at about 19.8 km. (a) Processing result of long-pulse echo signal with coherent degradation by the proposed method under different random phase-matching frequencies; (b) comparison of the frequency spectrum before and after being processed by this method.