We present an evaluation of airborne intensity‐modulated continuous‐wave (IM‐CW) lidar measurements of atmospheric column CO₂ mole fractions during the Atmospheric Carbon and Transport–America (ACT‐America) project. This lidar system transmits online and offline wavelengths simultaneously on the 1.57111‐μm CO₂ absorption line, with each modulated wavelength using orthogonal swept frequency waveforms. After the spectral characteristics of this system were calibrated through short‐path measurements, we used the HITRAN spectroscopic database to calculate the average‐column CO₂ mole fraction (XCO₂) from the lidar‐measured optical depths. Using in situ measurements of meteorological parameters and CO₂ concentrations for calibration data, we demonstrate that our lidar CO₂ measurements were consistent from season to season and had an absolute calibration error (standard deviation) of 0.80 ppm when compared to XCO₂ values calculated from in situ measurements. By using a 10‐s or longer moving average, a precision of 1 ppm or better was obtained. The estimated CO₂ measurement precision for 0.1‐, 1‐, 10‐, and 60‐s averages was determined to be 3.4, 1.2, 0.43, and 0.26 ppm, respectively. These correspond to measurement signal‐to‐noise ratios of 120, 330, 950, and 1,600, respectively. The drift in XCO₂ over 1‐hr of flight time was found to be below 0.1 ppm. These analyses demonstrate that the measurement stability, precision, and accuracy are all well below the thresholds needed to study synoptic‐scale variations in atmospheric XCO₂.

中文翻译：

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在ACT-America战役期间根据强度调制连续波差分吸收激光雷达测量结果对色谱柱CO2回收进行现场评估

在大气碳和运输美国（ACT-America）项目期间，我们对大气柱CO ₂摩尔分数的机载强度调制连续波（IM-CW）激光雷达测量结果进行了评估。该激光雷达系统在1.57111μmCO ₂吸收线上同时传输在线和离线波长，每个调制波长均使用正交扫描频率波形。通过短程测量对系统的光谱特性进行校准后，我们​​使用HITRAN光谱数据库从激光雷达测得的光学深度计算出了平均柱CO ₂摩尔分数（XCO ₂）。使用气象参数和CO _2的原位测量浓度的校准数据，我们证明了我们的激光雷达CO ₂测量值每个季节都是一致的，并且与从现场测量值计算得出的XCO ₂值相比，其绝对校准误差（标准偏差）为0.80 ppm 。通过使用10 s或更长的移动平均值，可以获得1 ppm或更高的精度。确定的0.1、1、10、60秒平均值的估计CO ₂测量精度分别为3.4、1.2、0.43和0.26 ppm。这些分别对应于120、330、950和1,600的测量信噪比。XCO _2中的漂移发现超过1小时的飞行时间低于0.1 ppm。这些分析表明，测量稳定性，精度和准确度均远低于研究大气XCO _2的天气尺度变化所需的阈值。