黑河生态水文遥感试验：水文气象观测网数据集（四道桥超级站涡动相关仪-2017）

该数据集包含了2017年1月1日至2017年12月31日的黑河水文气象观测网下游四道桥超级站的涡动相关仪观测数据。站点位于内蒙古额济纳旗四道桥，下垫面是柽柳。观测点的经纬度是101.1374E, 42.0012N，海拔873 m。涡动相关仪的架高8m，采样频率是10Hz，超声朝向是正北向，超声风速温度仪（CSAT3）与CO2/H2O分析仪（Li7500）之间的距离是15cm。
涡动相关仪的原始观测数据为10Hz，发布的数据是采用Eddypro软件处理的30分钟数据，其处理的主要步骤包括：野点值剔除，延迟时间校正，坐标旋转（二次坐标旋转），频率响应修正，超声虚温修正和密度（WPL）修正等。同时对各通量值进行质量评价，主要是大气平稳性（Δst）和湍流相似性特征（ITC）的检验。对Eddypro软件输出的30min通量值也进行了筛选：（1）剔除仪器出错时的数据；（2）剔除降水前后1h的数据；（3）剔除10Hz原始数据中每30min内缺失率大于10%的数据；（4）剔除夜间弱湍流的观测数据（u*小于0.1m/s）。观测数据的平均周期为30分钟，一天48个数据，缺失数据标记为-6999。4月7-8日由于涡动系统的Li7500标定，数据缺失；因仪器漂移等原因引起的可疑数据用红色字体标识。
发布的观测数据包括：日期/时间Date/Time，风向Wdir（°），水平风速Wnd（m/s），侧向风速标准差Std_Uy（m/s），超声虚温Tv（℃），水汽密度H2O（g/m3），二氧化碳浓度CO2（mg/m3），摩擦速度Ustar（m/s），奥布霍夫长度L（m），感热通量Hs（W/m2），潜热通量LE（W/m2），二氧化碳通量Fc（mg/(m2s)），感热通量的质量标识QA_Hs，潜热通量的质量标识QA_LE，二氧化碳通量的质量标识QA_Fc。感热、潜热、二氧化碳通量的质量标识分为三级（质量标识0:（Δst <30, ITC<30）; 1: （Δst <100, ITC<100）; 其余为2）。数据时间的含义，如0:30代表0:00-0:30的平均；数据以*.xls格式存储。
水文气象网或站点信息请参考Li et al. (2013)，观测数据处理请参考Liu et al. (2011)。

This dataset contains eddy covariance system observation data from the Sidaoqiao Super Station, which is located downstream of the Heihe Hydrometeorological Observation Network, during the period from January 1, 2017 to December 31, 2017. The station is situated in Sidaoqiao, Ejina Banner, Inner Mongolia, with its underlying surface covered by Tamarix. The coordinates of the observation point are 101.1374°E, 42.0012°N, and the elevation is 873 m. The eddy covariance system has an installation height of 8 m, a sampling frequency of 10 Hz, with the ultrasonic anemometer oriented towards true north. The distance between the ultrasonic anemometer-temperature sensor (model CSAT3) and the CO2/H2O analyzer (model Li7500) is 15 cm.

The raw observation data of the eddy covariance system is at 10 Hz, and the released data consists of 30-minute averaged data processed with EddyPro software. The main processing steps include: outlier removal, time lag correction, coordinate rotation (double coordinate rotation), frequency response correction, ultrasonic virtual temperature correction, and WPL density correction, etc. Quality assessment was also conducted for each flux value, mainly involving tests of atmospheric stationarity (Δst) and turbulence similarity characteristics (ITC). Further screening was performed on the 30-minute flux values output by EddyPro: (1) Remove data collected during instrument malfunctions; (2) Remove data within 1 hour before and after precipitation events; (3) Remove data with a missing rate exceeding 10% in every 30-minute segment of 10 Hz raw data; (4) Remove nighttime weak turbulence observation data (u* < 0.1 m/s). The average period of the observation data is 30 minutes, yielding 48 data points per day. Missing data is marked as -6999. Data from April 7 to 8 is missing due to the calibration of the Li7500 in the eddy covariance system. Suspicious data caused by instrument drift and other factors are marked in red font.

The released observation data includes: Date/Time, wind direction Wdir (°), horizontal wind speed Wnd (m/s), lateral wind speed standard deviation Std_Uy (m/s), ultrasonic virtual temperature Tv (℃), water vapor density H2O (g/m³), carbon dioxide concentration CO2 (mg/m³), friction velocity Ustar (m/s), Obukhov length L (m), sensible heat flux Hs (W/m²), latent heat flux LE (W/m²), carbon dioxide flux Fc (mg/(m²s)), quality flag of sensible heat flux QA_Hs, quality flag of latent heat flux QA_LE, and quality flag of carbon dioxide flux QA_Fc. The quality flags for sensible heat, latent heat, and carbon dioxide fluxes are divided into three levels: Flag 0: (Δst < 30, ITC < 30); Flag 1: (Δst < 100, ITC < 100); the remaining cases are Flag 2. The meaning of the data timestamp: for example, 0:30 represents the average value of the period 0:00-0:30. All data is stored in *.xls format.

For information regarding the hydrometeorological network or the station, please refer to Li et al. (2013); for details on the observation data processing, please refer to Liu et al. (2011).