The causation of MFJE (Modulation Frequency Jitter and Excursion) is generally introduced,and the error of MFJE in coherent detection is analyzed at the same time, the mathematic models of MFJE error in analog and digital coherent detection process are built. Based on the mathematic models, the effects of MFJE on analog and digital coherent modulation-demodulation process are identified, especially the effect of MFJE on discrete sampling. Finally, a Membership Weighted Function Sampling (MWFS) algorithm is proposed. The experimental result shows that the precision of coherent detection has not been affected in a modulation frequency excursion range of ± 9.2 % with MWFS,compared with the range of ±3% without MWFS. The result also shows that the mathematic models of MFJE error in analog and digital coherent detection process are valuable in coherent detection application field and MWFS proposed in the paper can eliminate the effect of modulation frequency excursion on coherent detection efficiently, which has been certified in practice.

After fixing on the divergent angle,peak power of laser pulse,parameters of received optical system and the geometrical configuration betweeh laser and received optical system, a faint target image of longer range with higher resolution obtained by active imaging system is constrained by imaging and processing technologies. With longer range and limited laser energy, it is impossible to illuminate the entire scene at once, and the illuminance obtained by each receiver pixel of CCD can not achieve an adequate level. In order to increase the imaging range of imaging system with given per-pulse laser en ergy, and to reduce atmospheric turbulence effects on image resolution, multi pulses may be employed to obtain image data over the whole scene and radiometric conceptions are used to establish the maximum scene illumination region during each exposure. A unique multiframe postprocessing technique is investigated in this paper. It is shown that in the presence of atmospheric turbulence and coherent speckle effects, this approach can produce superior results to conventional scene flood illumination.