Wind erosion flux, meteorology, soil roughness, and crop characteristics collected on a barley field in Dar Dhaoui (Tunisia) during 2015-2016

Data distributed here are part of the data acquired in Dar Dhaoui (southern Tunisia) during the 2015-2016 agricultural year. The objective of the experiment was to document wind erosion and its drivers on a traditionally cultivated barley field. The distributed data document 1) the saltation flux, 2) the meteorological parameters (wind speed and direction, rainfall, air temperature and relative humidity), 3) the daily median aerodynamic roughness length, and 4) barley characteristics (height and surface cover rate) collected from 01/10/2015 to 11/11/2016. Data include: (1) saltation flux: saltation flux was monitored on 3 masts located at the borders of the plot (West, East, and South). Each mast was equipped with four Big Spring Number Eight (BSNE) sand traps (Fryrear, 1986) mounted at heights of about 7, 16, 31, and 45 cm above ground level (agl), and with a large wind vane so that the opening of all BSNE always faced the wind. The three highest BSNEs on the mast had an opening of 10 cm² while the lowest one had a smaller opening (2 cm²). After accounting for the collection efficiency of the sand traps (assumed to be 100% as suggested by Goossens et al. (2000)), the saltation flux was computed by vertical integration of the cumulative masses collected at the 4 heights using the exponential formula proposed by Williams (1964). (2) meteorological parameters: wind speed and direction were measured at 2 m agl using a 2 dimensional (2D) sonic anemometer (WindSonicTM Gill Instruments Ltd), and rainfall using an ARG100 Tipping Bucket rain gauge (Campbell® Scientific company). Data were acquired using a CR200X data logger (Campbell® Scientific company), with a nominal data acquisition time of 5-min for all parameters measured with a frequency of 0.1 Hz. Given the high variability of both wind speed and direction on a 5-min time step, the maximum and mean values of wind speed, and the mean and standard deviation of wind direction measured over this interval were recorded. 5-min rainfall corresponds to the accumulated bucket tippings over this interval with one tipping corresponding to 0.2 mm of rainfall. (3) aerodynamic roughness length (15-min. averages): aerodynamic roughness length, z0, was estimated by fitting the logarithmic law of the wind speed vertical profile. This profile was determined using 7 cup anemometers (A100R Vector Instrument®) positioned at 0.285 m, 0.825 m, 1.395 m, 1.920 m, 2.965 m, 4.060 m, and 5.005 m (agl). The mast was located at the eastern edge of the plot. Data were acquired using a CR1000 data logger (Campbell® Scientific company), with a nominal data acquisition time of 1-min. (4) barley features: five plots of 2 m x 1.5 m were delimited in the field to weekly follow the barley height and cover rate using photographs and eye estimate. Barley height was measured by using a meter tape. The mean maximum height of the barley tufts was measured for each plot. Barley cover rate was always estimated by the same observer on site. When barley was green, its cover rate was also estimated following Mougin et al. (2014) by a numerical treatment (CAN-EYE© software) to corroborate eye estimates. Vertical and horizontal photographs were used to check the estimates.

本处发布的数据为2015-2016农业年度期间在突尼斯南部达尔·达维（Dar Dhaoui）采集数据的一部分。本实验旨在记录传统耕作大麦田的风蚀现象及其驱动因素。发布的数据记录了2015年10月1日至2016年11月11日期间采集的以下内容：1）跃移通量（saltation flux）；2）气象参数（风速与风向、降雨量、气温及相对湿度）；3）日平均空气动力学粗糙度长度；4）大麦特征（株高及地表覆盖率）。

（1）跃移通量：在试验田边界（西、东、南侧）设置3个观测杆监测跃移通量。每个观测杆配备4个Big Spring Number Eight（BSNE）沙陷阱（Fryrear，1986），分别安装于距地面约7 cm、16 cm、31 cm及45 cm高度处（agl），并配有大型风向标以确保所有BSNE沙陷阱的开口始终朝向来风方向。观测杆上位置最高的3个BSNE沙陷阱开口面积为10 cm²，最低处的开口面积较小（2 cm²）。在考虑沙陷阱的采集效率（参考Goossens等（2000）的建议，假设效率为100%）后，采用Williams（1964）提出的指数公式，对4个高度处采集的累积质量进行垂直积分，从而计算跃移通量。

（2）气象参数：在距地面2 m高度处（agl），使用二维（2D）声波风速仪（WindSonicTM，Gill Instruments Ltd）测量风速与风向，使用ARG100翻斗式雨量计（Campbell® Scientific公司）测量降雨量。数据通过CR200X数据采集器（Campbell® Scientific公司）获取，所有参数的标称采集时间为5分钟，测量频率为0.1 Hz。考虑到5分钟时间步长内风速与风向的高度变异性，记录该时段内风速的最大值与平均值，以及风向的平均值与标准差。5分钟降雨量为该时段内翻斗的累积翻转次数，每翻转一次对应0.2 mm降雨量。

（3）空气动力学粗糙度长度（15分钟平均值）：通过拟合风速垂直剖面的对数定律估算空气动力学粗糙度长度z0。该剖面由7个杯式风速仪（A100R，Vector Instrument®）测定，风速仪分别安装于距地面0.285 m、0.825 m、1.395 m、1.920 m、2.965 m、4.060 m及5.005 m高度处（agl）。观测杆位于试验田东边缘。数据通过CR1000数据采集器（Campbell® Scientific公司）获取，标称采集时间为1分钟。

（4）大麦特征：在试验田中划定5个2 m×1.5 m的子区，每周通过照片拍摄与目视估算跟踪大麦株高及覆盖率。大麦株高使用卷尺测量，每个子区测量大麦丛的平均最大高度。大麦覆盖率始终由同一观测者在现场估算；当大麦处于绿色期时，参考Mougin等（2014）的方法，通过数值处理（CAN-EYE©软件）估算覆盖率，以验证目视估算结果。垂直与水平方向的照片用于核对估算值。