森林冠层光谱与林下背景光谱尺度差异分析

林下植被作为森林生态系统的重要组成部分,在维护森林生态系统植物多样性和稳定性方面发挥着巨大作用。当前冠层光谱与林下背景光谱间的尺度差异尚不明确,限制了单角度光学遥感技术在林下植被研究中的应用。借助几何光学模型4-scale分析了森林背景光谱与冠层光谱的相关关系。结果表明,森林背景光谱与冠层光谱之间的尺度差异因森林结构的不同而变化,植被指数运算并不能消除尺度差异。冠层和背景光谱之间的尺度差异可以通过线性函数描述,这种线性关系随波长和森林结构的不同而不同,而模型参数与叶面积指数高度相关,在680 nm和865 nm处的决定系数分别为0.881、0.834 3、0.890 6和0.880 3。相关研究能为削弱或消除冠层光谱与林下背景光谱间的尺度差异提供参考。

一种玉米苗期冠层叶片营养诊断动态光谱指数

为了有效的解决玉米苗期冠层叶片营养状态车载动态诊断过程中,土壤干扰信息无法剔除的问题,本文提出了一种动态测量用光谱指数MPRI,根据MPRI的构成和特点、论述了利用MPRI辨识土壤与冠层光谱信息的机理,构建了基于MPRI的玉米苗期冠层叶片叶绿素含量的预测模型,通过车载式作物长势检测系统平台,运用模型对玉米苗期冠层叶片营养状态进行动态诊断与评估,取得良好的效果。研究表明:在车载动态条件下测量玉米苗期冠层叶片营养状态时,土壤的MPRI呈正值而玉米冠层的MPRI呈负值,因此使用光谱指数MPRI能够有效识别土壤背景与冠层叶片光谱信息。设定固定的阈值,能够较为准确和便捷的去除土壤背景光谱信息。基于MPRI构建的冠层叶片叶绿素含量的动态测量预测模型,能够准确的表征冠层叶片的叶绿素含量,模型决定系数R2达0.72,动态测量中对植株冠层的识别率达80%。与其他常用的指数相比,在车载动态测量环境下,光谱指数MPRI具有土壤背景信息识别速度快、正确率高,模型预测精度良好等特点,为玉米苗期冠层营养状态的诊断提供了新的途径。

红外探测器光谱响应测量系统

用迈克尔逊干涉仪及辅助检测平台建立了红外探测器光谱响应测量系统。利用计算机技术对被测红外探测器接收到的干涉图进行了傅里叶变换,得到了相对响应于入射波长的光谱响应曲线,并采用同时检测参考探测器光谱响应的方法,通过比较及运算,消除了背景光谱的影响。

光谱学与光谱技术

O433 2000020836正交投影用于红外光谱图中光谱提出及背景扣除=Spectra extraction and background correctionfor infrared absorption spectra via orthogonalprojections approach[刊,中]/张小吐,牟志春(青岛卫生检疫局.山东,青岛(266001)),祝惠英(青岛市环境监测站.山东,青岛(266001))//光谱实验室.-1999,16(3).-290-293用正交投影方法以及原始信号及其投影与背景矢量之间的线性关系确定背景光谱,从而将待测组分的红外光谱从混合物中提取出来。

利用开放光路傅里叶变换红外方法监测地表臭氧含量及分析

基于自研傅里叶变换红外光谱仪设计实现了开放光路臭氧在线监测系统,将计算机合成背景光谱方法与非线性最小二乘方法相结合进行定量分析,利用HITRAN数据库信息和仪器线型合成背景光谱,通过非线性最小二乘法反演出臭氧浓度,提高了测量精度和检测限,讨论了系统检测限测量方法,在16次平均情况下系统检测限达到1.42nmol.mol-1,利用此系统,对合肥市郊的地表臭氧浓度开展了连续监测实验,分析了浓度日变化以及月变化趋势与臭氧产生源之间的关系。结果表明,系统测量准确可靠,为我国臭氧监测提供了一种新的设备和方法。

Background correction in near-infrared spectra of plant extracts by orthogonal signal correction

In near-infrared (NIR) analysis of plant extracts, excessive background often exists in near-infrared spectra. The detection of active constituents is difficult because of excessive background, and correction of this problem remains difficult. In this work, the orthogonal signal correction (OSC) method was used to correct excessive background. The method was also compared with several classical background correction methods, such as offset correction, multiplicative scatter correction (MSC), standard normal variate (SNV) transformation, de-trending (DT), first derivative, second derivative and wavelet methods. A simulated dataset and a real NIR spectral dataset were used to test the efficiency of different background correction methods. The results showed that OSC is the only effective method for correcting excessive background.

A background refinement method based on local density for hyperspectral anomaly detection

For anomaly detection,anomalies existing in the background will affect the detection performance.Accordingly,a background refinement method based on the local density is proposed to remove the anomalies from thebackground.In this work,the local density is measured by its spectral neighbors through a certain radius which is obtained by calculating the mean median of the distance matrix.Further,a two-step segmentation strategy is designed.The first segmentation step divides the original background into two subsets,a large subset composed by background pixels and a small subset containing both background pixels and anomalies.The second segmentation step employing Otsu method with an aim to obtain a discrimination threshold is conducted on the small subset.Then the pixels whose local densities are lower than the threshold are removed.Finally,to validate the effectiveness of the proposed method,it combines Reed-Xiaoli detector and collaborative-representation-based detector to detect anomalies.Experiments are conducted on two real hyperspectral datasets.Results show that the proposed method achieves better detection performance.

Double beam near-infrared spectrometer for compensation of background water absorption and instrumental drift in intensity

A double beam near-infrared spectrometer is developed to compensate the water absorption and instrumental drift in intensity. The spectrometer may be used for both single and double beam measurements,and the two operation modes are compared. The results show that the double beam technique eliminates instrumental drift in the single beam measurement and therefore the stability of the system increases by more than 20%. The compensation of the double beam system on water absorption is verified by the measurement of fat content in milk. The results show that the spectrum data based on double beam mode get better calibration model and lower prediction error than traditional single beam mode.

Instantaneous Real-Time Detection Technology of GLI on FY-4 Geostationary Meteorological Satellite

Lightning is a typical example of an instantaneous random point source target. It has close connection with severe convective phenomena such as a thunderstorm, whose distribution, variation, position and forecasting can be acquired through lightning observation. In this paper, we discuss the way to achieve instantaneous lightning signal intensification and detection from geostationary orbit by using the differences between the lightning signal and the slowly changing background noise such as that of cloud, land and ocean, combining three methods, spectral filtering, spatial filtering and background noise, enabling removal between frames. After six months of operation in orbit, lightning within the coverage of the Geostationary Lightning Imager was effectively detected, strongly supporting the case for shorttime and real-time early warning, forecasting and tracking of severe convective phenomena in China.