AIRCRAFT FLUX-DETRENDED: UNIV. COL. (FIFE)

The NCAR King Air participation in FIFE-1987 and FIFE-1989 was part of a coordinated atmospheric boundary layer component which included other aircraft, surface measurements, balloon-borne profiles, SODAR, and lidar remote sensing. The chief objective of the boundary layer component was to describe the structure of the atmospheric boundary layer over the FIFE study area, increase knowledge of the physical processes active in the daytime boundary layer, and explore the relationship of surface properties to the time and spatial variation in the structure of the boundary layer. The phenomena studied were the daytime convective boundary layer structure and physical processes. This study used airborne measurement of vertical and horizontal wind gusts, humidity, potential temperature, mean horizontal wind speed, and horizontal linear trends of temperature, humidity, radiation. Fluxes of sensible heat, moisture, and momentum were estimated from fast response wind gust, temperature, and humidity measurements; these fluxes were evaluated from data whose linear trend and mean were removed. In addition several radiation parameters were also measured.. Several radiation parameters were also measured (e.g., global short and longwave, upwelling, and downwelling). Altitude of the aircraft was measured by radar and pressure; radar was more accurate but was only valid below about 930 m. Geographical position was measured by an inertial navigation system. All level legs of a flight mission were flown at a constant pressure altitude, thus the altitude of the aircraft over the surface varied. In general, the detrended data set is of excellent overall quality with very little loss of data. Vertical winds were sampled at an effective rate of 5 samples per second instead of the customary 10 samples per second; this had negligible effect on the fluxes but could compromise estimates of turbulence dissipation. Fluxes were estimated using raw, detrended and high-pass filtered data. From extensive analysis the FIFE Boundary Layer Group recommends using the detrended data.

美国国家大气研究中心（National Center for Atmospheric Research, NCAR）的空中国王（King Air）型飞机参与1987年与1989年的FIFE实验，属于协同式大气边界层观测子项目的组成部分，该子项目涵盖其他航空器、地面观测、气球载廓线测量、声雷达（SODAR）与激光雷达（lidar）遥感技术。
该大气边界层子项目的核心目标为：刻画FIFE研究区域内大气边界层的结构特征，加深对日间边界层活跃物理过程的认知，并探索地表属性与边界层结构的时间、空间变化之间的关联。本次研究聚焦的现象为日间对流边界层结构与相关物理过程。
本研究通过机载平台测量垂直与水平阵风、湿度、位温、平均水平风速，以及温度、湿度、辐射的水平线性趋势。感热、水汽与动量通量通过快速响应的阵风、温度与湿度观测数据估算得到；此类通量的评估基于移除线性趋势与均值后的数据。此外，研究还同步测量了多项辐射参数，涵盖全球短波与长波辐射、上行辐射与下行辐射。
飞机高度通过雷达与气压传感器进行测量：雷达测量精度更高，但仅在约930米以下的高度范围内有效。飞机地理位置通过惯性导航系统（inertial navigation system）获取。飞行任务中的所有水平航段均以恒定气压高度飞行，因此飞机相对于地表的高度会发生变化。
总体而言，去趋势后的数据集整体质量优异，数据丢失率极低。垂直风场的有效采样速率为每秒5次，而非常规的每秒10次；该采样速率对通量估算的影响可忽略不计，但可能会削弱湍流耗散率的估算精度。通量估算可采用原始数据、去趋势数据与高通滤波后的数据开展。经大量分析论证，FIFE边界层研究组推荐使用去趋势后的数据集。