A single probe fibre optic fluorosensor for marine and freshwater measurements of phytoplankton populations

A white light optical fibre fluorosensor for water quality measurements of the phytoplankton population is reported. The excitation light is amplitude modulated and a phase sensitive detection system is employed. The spectral properties of two typical samples of phytoplankton obtained off the coast of Scotland have been characterised and used in laboratory tests of the fluorosensor. Initial results show that this system is capable of resolving fluorescein concentrations in water of 10^?8mol 1^?1 and phytoplankton populations of 0.1 μgl.     

后向散射系数的贝叶斯估计

后向散射系数是合成孔径雷达图像中重要的物理参数.由于合成孔径雷达测量系统的噪声干扰和其他不确定因素影响使得测量数据往往不够精确,这就需要对测量数据进行合理估计.为了对后向散射系数做出准确合理的估计,文章将后向散射系数的先验知识考虑进去,给出了后向散射系数的三种贝叶斯估计算法.贝叶斯估计的关键是概率密度模型的选取.例中选用贝塔(Beta)分布作为先验概率密度模型,伽玛(Gamma)分布作为条件概率密度模型得到了合理的估计结果,并与最大似然估计(ML)算法进行了比较,比较结果表明在对后向散射系数的估计中,贝叶斯估计算法要明显优于最大似然估计算法.     

Computation of Nonlinear Backscattering Using a High-Order Numerical Method

The nonlinear Schrödinger equation (NLS) is the standard model for propagation of intense laser beams in Kerr media. The NLS is derived from the nonlinear Helmholtz equation (NLH) by employing the paraxial approximation and neglecting the backscattered waves. In this study we use a fourth-order finite-difference method supplemented by special two-way artificial boundary conditions (ABCs) to solve the NLH as a true boundary value problem. Our numerical methodology allows for a direct comparison of the NLH and NLS models and, apparently for the first time, for an accurate quantitative assessment of the backscattered signal.     

二次散射对脉冲激光雷达回波功率的影响

理论上分析了二次散射对大气脉冲激光雷达回波功率的影响并提出一种计算方法。采用某型大气激光雷达的测试结果与理论计算具有较强的一致性,证明了理论结果的正确性。根据二次散射回波信号的特点,选用适当的滤波方法将其影响降至最低。二次散射的理论计算解释了实测中发现的＂纹波＂现象,纹波的幅度和频率与雷达自身特性及粒子特性相关,其衰减速度较单次散射慢得多。因此对于大气探测具有进一步研究的重要价值。     

基于PXI总线DSP系统的设计

设计了一种基于PXI总线的DSP雷达信号处理模块,该模块依托高速的虚拟仪器总线技术,以DSPs、FPGA技术为核心,结合高效的DSP算法,能够完成高速的数据采集和信号处理功能,对高速的雷达系统处理器的研究具有重要意义.     

不同入射角下的雷达后向散射系数图像模拟

选择了新疆渭库三角洲(库车县、新和县、沙雅县)为实验区,利用Ulaby和Chapp的后向散射模型分别模拟了HV极化和HH极化的入射角为20°、24°、30°、33°、37°和40°的雷达后向散射系数图像。分析了不同入射角下图像各点后向散射系数值的散点图以及统计特征,得出由于入射角度的变化,两种极化的图像后向散射系数值变化较大,其变化趋势均符合余弦函数曲线分布,且模拟SAR图像很好的保留了地面散射信息。     

Backscattering of electromagnetic waves by non-spherical raindrops in double-frequency radar

The article is devoted to solving the actual scientific task of restoration of precipitation microstructural characteristics by double-frequency remote sensing with a glance of rain particles nonsphericity. At that, the calculations of radar cross section of raindrops were performed by approximated methods on the basis of spherical drops of equivalent volume and dipole scattering. Results obtained are compared with the calculations of the rigorous method of moments. It was shown that errors of approximate calculations of backscattering characteristics are smaller for the same vertical polarization of frequency channels of double-frequency radar. In addition, the behaviour of the differential backscattering cross section is studied.     

Ku波段成像散射计后向散射系数精度分析

成像微波散射计是增加了成像功能的新型散射计系统,其后向散射系数的测量精度仍然是系统的关键指标.根据成像微波散射计的系统特点,提出了基于FFT对信号与噪声进行同时测量的数字处理系统,推导了适用于衡量成像散射计后向散射系数测量精度的归一化标准差Kp .对于不同观测条件下的Kp 进行了公式描述及数值仿真.得出不同区域和不同目标观测情况下如何配置系统参数的结论,并落实到成像散射计系统的性能分析中,对如何折衷设计性能参数并在实验过程中获取最佳试验结果进行理论指导.     

基于SAR后向散射的海上溢油检测研究

应用海面雷达后向散射系数检测海上溢油是目前海上溢油遥感监测的一个重要方向。本文以南海Envisat-ASAR数据为例,在分析SAR数据的基础上,应用Envisat-ASAR绝对定标计算方法,计算后向散射系数,研究应用SAR进行海上溢油遥感监测的散射特性,计算目标与海面边界后向散射系数梯度均值0σ与目标与海面后向散射系数均值差Δμ,并以两者结合作为区分海面油膜与自然现象的解译标志,从而为溢油识别提供依据。     

Remote sensing of phytoplankton functional types

The principal goal in early missions of satellite-borne visible spectral radiometry (ocean colour) was to create synoptic fields of phytoplankton biomass indexed as concentration of chlorophyll-a. In the context of climate change, a major application of the results has been in the modelling of primary production and the ocean carbon cycle. It is now recognised that a partition of the marine autotrophic pool into a suite of phytoplankton functional types, each type having a characteristic role in the biogeochemical cycle of the ocean, would increase our understanding of the role of phytoplankton in the global carbon cycle. At the same time, new methods have been emerging that use visible spectral radiometry to map some of the phytoplankton functional types. Here, we assess the state of the art, and suggest paths for future work.     

A Fully-Passive Wireless Microsystem for Recording of Neuropotentials using RF Backscattering Methods

The ability to safely monitor neuropotentials is essential in establishing methods to study the brain. Current research focuses on the wireless telemetry aspect of implantable sensors in order to make these devices ubiquitous and safe. Chronic implants necessitate superior reliability and durability of the integrated electronics. The power consumption of implanted electronics must also be limited to within several milliwatts to microwatts to minimize heat trauma in the human body. In order to address these severe requirements, we developed an entirely passive and wireless microsystem for recording neuropotentials. An external interrogator supplies a fundamental microwave carrier to the microsystem. The microsystem comprises varactors that perform nonlinear mixing of neuropotential and fundamental carrier signals. The varactors generate third-order mixing products that are wirelessly backscattered to the external interrogator where the original neuropotential signals are recovered. Performance of the neuro-recording microsystem was demonstrated by wireless recording of emulated and in vivo neuropotentials. The obtained results were wireless recovery of neuropotentials as low as approximately 500 microvolts peak-to-peak (μV(pp)) with a bandwidth of 10 Hz to 3 kHz (for emulated signals) and with 128 epoch signal averaging of repetitive signals (for in vivo signals).     

基于遗传算法和雷达后向散射模型的地表参数反演研究

在地表自然裸露条件下,利用雷达后向散射系数反演地表粗糙度及地表土壤含水量已经开展了很多的研究,许多学者提出了很多相关的模型及反演技术。在已有散射模型的基础上,利用遗传算法反演地表参数,并且对反演效果进行了验证;然后分别基于AIEM模型和Oh模型对SIR-C雷达图像进行了反演计算,并对反演结果作了统计分析,从而为利用雷达图像反演地表信息提供了新的研究思路。     

The identification of phytoplankton pigments from absorption spectra

The absorption spectra of photosynthetic algae are characterized by a continuous envelope, which is a result of the overlapping spectra of the indivual pigments. This feature makes it difficult to estimate the contribution of each pigment to the total absorption spectra. Derivative analysis is an objective tool for isolating absorption peaks in phytoplankton. Theoretically, electrons and ions of interacting molecules can be regarded as simple harmonic oscillators in an electromagnetic field, which result in a Lorentzian shape. However, when measured by an optical spectrophotometer the signal is transformed into a Gaussian curve. Thus, a combination of both types of curve provides a realistic approach to the decomposition of absorption spectra. In this study derivative analysis is performed on absorption spectra in order to prove that the method can be successfully used to identify the individual absorption spectra of component pigments. The spectra used are modelled phytoplankton, spectrophotometric measurements of algal cultures and samples from natural waters. A combination of Gaussian-Lorentzian shaped curves, centred on the identified peaks, were compared with the original spectra and showed good agreement.     

低能γ射线反散射法测量塑料薄膜厚度的研究

本文叙述了低能γ射线反散射法测量塑料薄膜的可能性，建立了塑料薄膜厚度与反散射γ射线强度的关系式。研制了一套测量装置，并对测量误差进行了分析。     

综合应用分支模型和天线阵理论对大豆冠层后向散射系数的研究

提出了一种新的方法来研究大豆冠层的极化后向散射系数。这种方法结合分支模型^〔1〕和PACT 模型^〔2〕的优点: 前者强调植物结构和相干效应的重要性; 后者则采用天线阵的概念来考虑植株间的相互作用, 适合应用于大豆等在耕作实践中通常具有准周期的作物。而且, 针对描述轴对称散射体取向的欧拉角和球坐标系统中的仰角、方位角的联系, 提出了更符合物理实际的新的关系。由我们的方法预测的后向散射系数和实验数据的良好吻合, 证明了其有效性。
     

基于高亮特征匹配的双视向SAR图像建筑物高度提取

由于城区场景的复杂性和SAR成像几何畸变的影响,基于单幅SAR图像的建筑物高度提取常常存在很大困难。针对这一问题,利用建筑物目标SAR成像形成的叠掩、二次散射、较强单次散射等散射机制对应的高亮特征非常典型,并且对方向性敏感的特点,提出了一种基于双视向SAR图像高亮特征与几何模型匹配的建筑物高度提取方法。首先分析了建筑物目标的SAR图像散射特征及对雷达视向的敏感性,然后构造了建筑物目标在双视向SAR图像上高亮特征几何模型,然后基于灰度均值、灰度概率分布、边界信息定义匹配函数,并利用多种群遗传算法进行优化求解,最终得到建筑物目标的高度信息。基于模拟和机载SAR图像的试验表明该方法的建筑物高度平均反演误差小于1m,可以有效提高建筑物高度反演的精度。     

Absorption spectrum of phytoplankton pigments derived from hyperspectral remote-sensing reflectance

For a data set collected around Baja California with chlorophyll-a concentration ((chl-a)) ranging from 0.16 to 11.3 mg/m³, hyperspectral absorption spectra of phytoplankton pigments were independently inverted from hyperspectral remote-sensing reflectance using a newly developed ocean-color algorithm. The derived spectra were then compared with those measured from water samples using the filter-pad technique, and an average difference of 21.4% was obtained. These results demonstrate that the inversion algorithm worked quite well for the coastal waters observed and suggest a potential of using hyperspectral remote sensing to retrieve both chlorophyll-a and other accessory pigments.     

Influence of phytoplankton pigment composition on remote sensing of cyanobacterial biomass

An extensive field campaign was carried out for the validation of a previously published reflectance ratio-based algorithm for quantification of the cyanobacterial pigment phycocyanin (PC). The algorithm uses band settings of the Medium Resolution Imaging Spectrometer (MERIS) onboard ENVISAT, and should accurately retrieve the PC concentration in turbid, cyanobacteria-dominated waters. As algae and cyanobacteria often co-occur, the algorithm response to varying phytoplankton composition was explored. Remote sensing reflectance and reference pigment measurements were obtained in the period 2001-2005 in Spain and the Netherlands using field spectroradiometry and various pigment extraction methods. Additional field data was collected in Spain in May 2005 to allow intercalibration of spectroradiometry and pigment assessment methods. Two methods for extraction of PC from concentrated water samples, and in situ measured PC fluorescence, compared well. Reflectance measurements with different field spectroradiometers used in Spain and the Netherlands also gave similar results. Residual analysis of PC predicted by the algorithm showed that overestimation of PC mainly occurred in the presence of chlorophylls b and c, and phaeophytin. The errors were strongest at low PC relative to Chl a concentrations. A correction applied for absorption by Chl b markedly improved the prediction. Without such a correction, the quality of the PC prediction still increased markedly with estimates > 50 mg PC m^− 3, allowing monitoring of the cyanobacterial status of eutrophic waters. The threshold concentration may be lowered when a high intracellular PC:Chl a ratio or cyanobacterial dominance is expected. Below the limit, predicted PC concentrations should be considered as the highest estimate. We evaluated that remote sensing of both PC and Chl a would allow assessment of cyanobacterial risk to water quality and public health in over 70% of our cases.     

Computer-aided manufacture of marine propellers

A unique computer-based method is presented of producing marine propellers of moderate size. The surfaces of the propeller are calculated from a table of offsets as an array of rectangular coordinate points and displayed on a graphics terminal where they can be examined and, if required, interactively modified. Ultimately a propeller, requiring only a minimum of hand finishing, is obtained using a numerically controlled milling operation.     

Applications of marine robotic vehicles

The ocean covers about two-thirds of the earth and has a great effect on the future existence of all human beings. About 37% of the world’s population lives within 100 km of the ocean. The ocean is generally overlooked as we focus our attention on land and atmospheric issues; we have not been able to explore the full depths of the ocean and its abundant living and non-living resources. For example, it is estimated that there are about 2,000 billion tons of manganese nodules on the floor of the Pacific Ocean near the Hawaiian Islands. We discovered, by using manned submersibles, that a large amount of carbon dioxide comes from the seafloor and extraordinary groups of organisms live in hydrothermal vent areas. Marine robots including unmanned surface vehicles and unmanned underwater vehicles can help us better understand marine and other environmental issues, protect the ocean resources of the earth from pollution, and efficiently utilize them for human welfare. This paper briefly presents some exemplary models of recent developments in marine robots in different application areas.