A method improving an accuracy of laser radar data affected by the systematic noise of photomultipliers.

概要

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In measuring atmospheric aerosol distributions over a wide range by a laser radar, systematic noise generated from a photomultiplier (PMT) is known as an important error factor.In order to investigate the characteristics of the systematic noise, an experiment has been made first to derive the response function of the PMT (RCA 8852) in this study. The response of the PMT to an impulse-like light exposure showed a long tail with the decay time of about 200μs. Then, the response function obtained from the data was applied to simulate the distortion of the laser radar signals. The result of the simulation well agreed with actual laser radar signals. According to the simulation, the component of the systematic noise took so much greater value than that of the real signal at the altitude over 50km that the systematic noise was estimated as an exponential function with the time constant of 200μs from the distorted laser radar signal.Based on the experimental results, a proposal is made of an efficient method to remove the systematic noise from the laser radar signals. The corrected laser radar signals by the proposed method closely agreed with the signal expected from a clean molecular atmosphere at the altitude over 30km.
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