An intensity modulated, continuous-wave (IM-CW) integrated path differential absorption (IPDA) fiber-based lidar is developed herein for measuring atmospheric carbon dioxide (CO₂). There are two main challenges in improving measurement accuracy, which have not been given enough attention in the previous research: one is that temperature sensitivity in optical components causes biases, due to the drift of component characteristic, and the other is that speckle noise deteriorates the signal-to-noise ratio. With the components thermally controlled, a target calibration accuracy of 0.003 dB is realized, corresponding to a CO₂ concentration precision of better than 1 ppm for a 1 km path. A moving diffuser can reduce speckle noise by time averaging. In this paper, movement of the diffuser is substituted by the perturbation of the emitted laser beam by using a vibrating motor mounted on the optical antenna. Selecting on and off wavelengths with a small wavelength separation can improve the correlation between two laser speckle fields. These improvements result in the improved accuracy of the IPDA lidar system. Finally, the lidar performance was analyzed after the improvements described above were implemented. The diurnal variations of the atmospheric CO₂ concentration using a topographic target were performed, and the results showed good agreement with the data measured by an in situ sensor. The root mean square (rms) of the deviation between the IPDA lidar and the in situ sensor was less than 1.4%.

中文翻译：

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用于大气CO2测量的IM-CW激光雷达的校准和改进的散斑统计

本文开发了一种基于强度调制的连续波（IM-CW）积分路径差分吸收（IPDA）光纤激光雷达，用于测量大气中的二氧化碳（CO ₂）。在提高测量精度方面存在两个主要挑战，在先前的研究中并未给予足够的重视：一个是光学组件中的温度灵敏度由于组件特性的漂移而引起偏差，另一个是散斑噪声使光学特性恶化。信噪比。通过对组件进行热控制，可以实现0.003 dB的目标校准精度，对应于CO ₂对于1 km的路径，浓度精度优于1 ppm。移动的扩散器可以通过时间平均来减少斑点噪声。在本文中，通过使用安装在光学天线上的振动电机，用发射的激光束的扰动代替了扩散器的运动。选择具有小的波长间隔的开和关波长可以改善两个激光散斑场之间的相关性。这些改进导致IPDA激光雷达系统的精度提高。最后，在实现上述改进之后，分析了激光雷达的性能。大气CO ₂的日变化使用地形目标进行浓缩，结果显示与原位传感器测得的数据吻合良好。IPDA激光雷达和原位传感器之间的偏差的均方根（rms）小于1.4％。