土壤表层湿度影响下冬小麦晚霜冻害及冠层光谱检测

为探究土壤表层湿度影响下冬小麦冠层光谱反射率响应晚霜冻害的特征,并检验敏感光谱波段预测小麦产量变化的能力,于2013和2014年小麦拔节期,分别设置了表层土壤含水量为10%(干)、10%~20%(中)和20%(湿)的三个湿度处理的冻前试验,并在低温室内进行降温处理。分析了不同土壤表层湿度下受冻冬小麦的穗数、穗粒数、千粒重、单株产量、冠层光谱反射率及其一阶微分值的差异,对冬小麦冻害产量变化率和高光谱特征参量进行了相关分析和一元线性拟合。结果表明:冬小麦穗粒数和单株产量总体上均随土壤表层湿度的降低而呈减少态势,在土壤表层干处理条件下冻害对冬小麦产量造成的影响最为显著(p0.05);在绿峰(523nm附近)、黄边(571nm附近)、红边(732nm附近)和近红外台的两个水分吸收带(952和1 145nm附近),干+冻害处理冬小麦冠层反射率的一阶微分值与中+冻害、湿+冻害处理的差值明显;剥离了土壤表层湿度对光谱的影响后,冬小麦冠层反射率一阶微分差值在以570nm为中心的黄边区域和以710nm为中心的红边区域对干、中和湿梯度处理下晚霜冻害响应的差异明显;两年试验中的黄边面积(SDy)和570nm处一阶微分值(d570)均与冻害产量变化率达到显著正相关(p0.05),说明黄边区域的高光谱特征参量可用于检测土壤表层湿度影响下的冬小麦晚霜冻害程度。本研究可为土壤表层湿度和晚霜冻害叠加影响下冬小麦产量变化预测方法的探讨提供参考。     

Acoustic multipath structure in direct zone of deep water and bearing estimation of tow ship noise of towed line array

In the towed line array sonar system, the tow ship noise is the main factor that affects the sonar performance. Conventional noise cancelling methods assume that the noise is towards the endfire direction of the array. An acoustic experiment employing a towed line array is conducted in the western Pacific Ocean, and a strange bearing-splitting phenomenon of the tow ship noise is observed in the array. The tow ship noise is split into multiple noise signals whose bearings are distributed between 10° and 90° deviating from the endfire direction. The multiple interferences increase the difficulty in recognizing the target for the sonar operator and noise cancellation. Therefore, making the mechanism clear and putting forward the tow ship noise splitting bearing estimation method are imperative. In this paper, the acoustic multi-path structure of the tow ship in deep water is analyzed. Then it is pointed out that the bearing-splitting phenomenon is caused by the main lobe of direct rays and bottom-reflected rays, as well as several side lobes of direct rays. Meanwhile, the indistinguishability between the elevation angle and the bearing angle due to the axial symmetry of a strict horizontal line array causes the bearing to deviate from the endfire direction. Based on the theory above, a method of estimating bearing of the tow ship noise in deep water is proposed. The theoretical analysis results accord with the experimental results, which helps to identify the target and provide correct initial bearing guidance for noise cancelation methods.