Fast-response infrared gas analyzers (IRGAs) have been widely used over 3 decades in many ecosystems for long-term monitoring of water vapor fluxes in the surface layer of the atmosphere. While some of the early IRGA sensors are still used in these national and/or regional eco-flux networks, optically improved IRGA sensors are newly employed in the same networks. The purpose of this study was to evaluate the performance of water vapor density and flux data from three generations of IRGAs – LI-7500, LI-7500A, and LI-7500RS (LI-COR Bioscience, Inc., Nebraska, USA) – over the course of a growing season in Bushland, Texas, USA, in an irrigated maize canopy for 90 d. Water vapor density measurements were in generally good agreement, but temporal drift occurred in different directions and magnitudes. Means exhibited mostly shift changes that did not impact the flux magnitudes, while their variances of water vapor density fluctuations were occasionally in poor agreement, especially following rainfall events. LI-7500 cospectra were largest compared to LI-7500RS and LI-7500A, especially under unstable and neutral static stability. Agreement among the sensors was best under the typical irrigation-cooled boundary layer, with a 14 % interinstrument coefficient of variability under advective conditions. Generally, the smallest variances occurred with the LI-7500RS, and high-frequency spectral corrections were larger for these measurements, resulting in similar fluxes between the LI-7500A and LI-7500RS. Fluxes from the LI-7500 were best representative of growing season ET based on a world-class lysimeter reference measurement, but using the energy balance ratio as an estimate of systematic bias corrected most of the differences among measured fluxes.

中文翻译：

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三代红外气体分析仪的水蒸气密度和湍流

快速响应的红外气体分析仪（IRGA）在过去的3年中已广泛用于许多生态系统中，以长期监测大气表层的水蒸气通量。尽管某些早期的IRGA传感器仍在这些国家和/或区域性的生态通量网络中使用，但光学改进的IRGA传感器又在同一网络中被新采用。这项研究的目的是评估三代IRGA（LI-7500，LI-7500A和LI-7500RS（LI-COR Bioscience，Inc.，美国内布拉斯加州））的水蒸气密度和通量数据的性能。在美国得克萨斯州布什兰的一个灌溉季节中，在灌溉的玉米冠层中生长90天。水蒸气密度的测量总体上吻合良好，但时间漂移发生在不同的方向和大小。平均值表现出大部分变化，但并不影响通量大小，而水蒸气密度波动的变化有时相差不大，尤其是在降雨事件之后。与LI-7500RS和LI-7500A相比，LI-7500共谱最大，特别是在不稳定和中性静态稳定性下。在典型的灌溉冷却边界层上，传感器之间的一致性最佳，在对流条件下，仪表间变异系数为14％。通常，LI-7500RS发生的变化最小，并且这些测量的高频频谱校正更大，导致LI-7500A和LI-7500RS之间的通量相似。根据世界一流的溶渗仪参考测量，LI-7500的助焊剂最能代表生长季的ET，