限量灌溉对冬小麦抗旱增产和水分利用的影响

小麦体积含水量是表征小麦生理状态、影响小麦产量的重要参数,传统的测量手段如人工采样烘干、卫星遥感等,难以实现小麦体积含水量的连续、动态、高精度监测,由此提出了一种利用全球导航卫星系统（global navigation satellite system,GNSS）折射测量技术反演小麦体积含水量的方法。首先,使用两组GNSS天线同时接收直射信号和穿透小麦植株层的折射信号,利用两信号的振幅比表示折射信号的衰减程度；然后,基于电磁波传播理论,建立了GNSS直射、折射信号的物理模型,并在此基础上导出小麦体积含水量、振幅比、小麦高度、气温的函数关系,进而构建了反演小麦体积含水量的数学模型。利用导航型GNSS设备采集的数据对所提方法进行了验证,结果表明,在小麦拔节期、抽穗期和成熟期,该方法反演的小麦含水量与人工实测数据符合较好；当小麦含水量在1~7 kg/m³范围内时,反演结果的平均误差、标准差和均方根误差分别为0.058 kg/m³、0.396 kg/m³、0.399 kg/m³。研究结果证明了利用导航型GNSS接收机准确获取植被含水量动态变化信息的可行性,为低成本、低功耗、小型化GNSS植被含水量监测设备的研制奠定了基础。

Water Relations in Winter Wheat as Drought Resistance Indicators

Wheat volumetric water content is one of the important variables in indication of wheat growth status, and it is essentially affecting the wheat yield. However, the traditional measuring techniques, such as manual sampling method and satellite remote sensing techniques, are difficult for monitoring wheat volumetric water content accurately and continuously. To solve this issue, we propose a new wheat volumetric water content estimating method with global navigation satellite system (GNSS) refractometry.First,we use two pairs of GNSS receivers and antennas to collect the refracted signal in the wheat crop layer and the direct signal in the air respectively. Amplitude attenuation degree of the refracted signal is quantified as the amplitude ratio of the refracted GNSS signal to the direct one, and the ratio can be derived from signal-to-noise ratio (SNR) observations collected by the two receivers. Mathematic relationship between the ratio, wheat volumetric water content, wheat height, and air temperature is described using the linear functions. Then, the inversion model of wheat volumetric water content, which takes the SNR at GNSS elevation angle of 55°, wheat height, and temperature as the inputs, is developed. Finally, the model is validated through a data set collected in an experimental campaign over 120 days.The results show that a good agreement exiting between the model calculated wheat volumetric water content estimations and manual sampling ones in the wheat stem extension, heading, and ripening stage, The mean, standard deviation and root mean square of model calculated wheat volumetric water content estimation error are 0.058 kg/m³, 0.396 kg/m³, 0.399 kg/m³ at 1 to 7 kg/m³.The proposed method can be used to monitor the volumetric water content of wheat accurately in a cost-effective way.