REFERENCES

environments with moving objects, the FSF-laser-based range finder is unacceptable. 1) FMCW Realized by Waveform Modulation: Chirped pulse laser sources can also be realized by modulating the intensity of the continuous-wave (CW) laser [12]. The system has the same problem as described in the previous section. In contrast to this approach, the National Aeronautics and Space Administration (NASA) Langely Research Center [11] developed waveform-modulated FMCW laser radar to aid the NASA new space exploration initiative for manned and robotic missions to the moon and Mars. Fig. 15 shows the transmitted (solid) and the received (dashed) linearly chirped triangular modu-lation functions. The target range R and speed V can be obtained, providing that the two frequencies fD and fU of the beat signal are measured. The method measures the target range and speed with high preci-sion. However, the period of the triangular modulation function in [11] is as long as 5 ms; therefore, the scanning speed of the laser radar is no larger than 200 times per second. To improve the scanning speed, the transmitted signal length should be as short as possible