Rothermel J, Chambers D M, Jarzembski M A, Srivastava V, Bowdle D A, Jones W D
Appl Opt. 1996 Apr 20;35(12):2083-95. doi: 10.1364/AO.35.002083.
Two continuous-wave (CW) focused CO(2) Doppler lidars (9.1 and 10.6 µm) were developed for airborne in situ aerosol backscatter measurements. The complex path of reliably calibrating these systems, with different signal processors, for accurate derivation of atmospheric backscatter coefficients is documented. Lidar calibration for absolute backscatter measurement for both lidars is based on range response over the lidar sample volume, not solely at focus. Both lidars were calibrated with a new technique using well-characterized aerosols as radiometric standard targets and related to conventional hard-target calibration. A digital signal processor (DSP), a surface acoustic wave spectrum analyzer, and manually tuned spectrum analyzer signal analyzers were used. The DSP signals were analyzed with an innovative method of correcting for systematic noise fluctuation; the noise statistics exhibit the chi-square distribution predicted by theory. System parametric studies and detailed calibration improved the accuracy of conversion from the measured signal-to-noise ratio to absolute backscatter. The minimum backscatter sensitivity is ~3 × 10(-12) m(-1) sr(-1) at 9.1 µm and ~9 × 10(-12) m(-1) sr(-1) at 10.6 µm. Sample measurements are shown for a flight over the remote Pacific Ocean in 1990 as part of the NASA Global Backscatter Experiment (GLOBE) survey missions, the first time to our knowledge that 9.1-10.6-µm lidar intercomparisons were made. Measurements at 9.1 µm, a potential wavelength for space-based lidar remote-sensing applications, are to our knowledge the first based on the rare isotope (12)C (18)O(2) gas.
研制了两台连续波（CW）聚焦二氧化碳多普勒激光雷达（波长分别为9.1和10.6微米），用于机载原位气溶胶后向散射测量。记录了可靠校准这两台配备不同信号处理器的系统以准确推导大气后向散射系数的复杂过程。两台激光雷达用于绝对后向散射测量的校准基于激光雷达采样体积上的距离响应，而非仅聚焦处的响应。两台激光雷达均采用一种新技术进行校准，该技术使用特性良好的气溶胶作为辐射标准目标，并与传统硬目标校准相关联。使用了数字信号处理器（DSP）、表面声波频谱分析仪和手动调谐频谱分析仪信号分析仪。采用一种创新方法对DSP信号进行分析，以校正系统噪声波动；噪声统计呈现出理论预测的卡方分布。系统参数研究和详细校准提高了从测量信噪比转换为绝对后向散射的准确性。在9.1微米波长处，最小后向散射灵敏度约为3×10⁻¹²米⁻¹球面度⁻¹，在10.6微米波长处约为9×10⁻¹²米⁻¹球面度⁻¹。给出了1990年在偏远太平洋上空飞行的样本测量结果，这是美国国家航空航天局全球后向散射实验（GLOBE）测量任务的一部分，据我们所知，这是首次进行9.1 - 10.6微米激光雷达的相互比较。据我们所知，9.1微米波长处的测量是首次基于稀有同位素（¹²C¹⁸O₂）气体进行的，该波长是天基激光雷达遥感应用的潜在波长。
