13 February 2001 Self-compensated coherent integration method for coherent lidar system
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Abstract
In this paper, a new signal processing method named SCCI (Self- Compensated Coherent Integration) which enables a coherent integration over a longer time, compared to a coherence time of a back-scattered signal, is proposed. A back-scattered signal is gated by a constant time gate of which a gate time is set to be shorter than a coherence time. Each gated signal is sampled as a former and a latter part. A gated signal in each part is integrated coherently by FFT. A cross spectrum of two parts is calculated in each time gate. Since a phase of a cross spectrum in each time gate is constant, this process is identified to a self-phase-compensation. A cross spectrum is integrated over all time gates. This process is identified to a coherent integration of a back-scattered signal over a signal length which is longer than a coherence time, since a phase of a cross spectrum in each time gate is constant. The signal to noise ratio (SNR) for SCCI is theoretically higher than that for PDI (Post Detection Integration) in the case of N>16/SNRP2 (N: Gate number, SNRp: SNR of a time gate for PDI) at low SNR. SCCI is superior to PDI in every case at low SNR if a required SNR in a system is up to 6dB and a Doppler frequency of a back-scattered signal is constant in a signal length. Furthermore, if SNRP becomes lower and lower, and a required SNR is higher and higher compared to 6dB, the effect of using SCCI appears more and more distinctly. We confirm the effect experimentally using a 1.5-µm wind sensing lidar system. Keywords: Coherent lidar, Coherent integration, Coherence time, Signal division, Self-compensation, Doppler frequency, Wind sensing, SNR, SCCI, PDI
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Shumpei Kameyama, Shumpei Kameyama, Takahiko Fujisaka, Takahiko Fujisaka, Kimio Asaka, Kimio Asaka, Toshiyuki Ando, Toshiyuki Ando, Yasuharu Koyata, Yasuharu Koyata, Yoshihito Hirano, Yoshihito Hirano, Shusou Wadaka, Shusou Wadaka, Toru Tajime, Toru Tajime, } "Self-compensated coherent integration method for coherent lidar system", Proc. SPIE 4153, Lidar Remote Sensing for Industry and Environment Monitoring, (13 February 2001); doi: 10.1117/12.417064; https://doi.org/10.1117/12.417064
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