Optical remote sensing of waters with vertical structure

Optical remote sensing of ocean color is a well-established technique that is used to produce maps of marine constituents on a routine basis. Retrieval algorithms used to infer pigment concentrations from measurements of ocean color are usually based on the assumption that the upper ocean column is vertically homogeneous. However, stable stratification of the water column is often encountered in coastal waters and in fjords. This stratification is decisive for the initiation, maintainance, and species composition of phytoplankton blooms. Here we present an optical remote-sensing algorithm with the ability to resolve such a vertical structure of oceanic waters. The vertical structure is assumed to consist of two homogeneous layers with different concentrations of chlorophyll a. The algorithm is designed to determine the chlorophyll-a concentrations of the two layers as well as the thickness of the upper layer. These three parameters influence the ocean color and are simultaneously retrieved through an inverse-modeling technique. This technique consists of using radiative-transfer computations for a coupled atmosphere-ocean system to simulate radiances received in various bands of the satellite sensor and to compare these simulated results with measured radiances. The sum of absolute values of differences between simulated and measured radiances is minimized by use of an optimization algorithm, and the retrieved parameters are those that yield the minimum sum of differences between measured and simulated data. The optimization algorithm that we used in our study is the simulated annealing method, which is an extension of the downhill simplex algorithm. In this study the algorithm was tested on synthetic data generated by the forward model. The results indicate that it should be possible to retrieve vertical variations in the pigment concentration. The synthetic data were generated for spectral bands that coincide with those of the Medium Resolution Imaging Spectrometer sensor, which will be a part of the instrument package of the upcoming Environmental Satellite.     

Optical remote sensing of marine constituents in coastal waters: a feasibility study

Optical remote sensing of ocean color is a well-established technique for inferring ocean properties. However, most retrieval algorithms are based on the assumption that the radiance received by satellite instruments is affected only by the phytoplankton pigment concentration and correlated substances. This assumption works well for open ocean water but becomes questionable for coastal waters. To reduce uncertainties associated with this assumption, we developed a new algorithm for the retrieval of marine constituents in a coastal environment. We assumed that ocean color can be adequately described by a three-component model made up of chlorophyll a, suspended matter, and yellow substance. The simultaneous retrieval of these three marine constituents and of the atmospheric aerosol content was accomplished through an inverse-modeling scheme in which the difference between simulated radiances exiting the atmosphere and radiances measured with a satellite sensor was minimized. Simulated radiances were generated with a comprehensive radiative transfer model that is applicable to the coupled atmosphere-ocean system. The method of simulated annealing was used to minimize the difference between measured and simulated radiances. To evaluate the retrieval algorithm, we used simulated (instead of measured) satellite-received radiances that were generated for specified concentrations of aerosols and marine constituents, and we tested the ability of the algorithm to retrieve assumed concentrations. Our results require experimental validation but show that the retrieval of marine constituents in coastal waters is possible.     

Comparison of chlorophyll a concentration detected by remote sensors and other chlorophyll indices in inhomogeneous turbid waters

A new analytical approach for retrieval of the vertically weighted chlorophyll a concentration (Chl(rs)) detected by remote sensors is presented. Model calculations were carried out for the turbid waters of Lake Kinneret, Israel, and showed that Chl(rs) may be replaced by the average chlorophyll a concentration (Chl(p)) within the upper "penetration layer" 0-Z(p). The study also showed a high correlation between Chl(rs) and Chl concentration averaged in the other depth layers, namely, the 0-1 m layer, the euphotic layer (0-Z(e)), and the production layer (0-Z(pr)). Our findings are closely related to models developed for the world ocean, with the exception of periods when the dinoflagellate Peridinium gatunense blooms in the lake. We showed the effect of the pattern of vertical Chl distributions within the penetration layer on the difference between Chl(rs) and other Chl indices was conspicuous when the Chl maximum was in the uppermost 0- m layer of the water column. We assume that the presented approaches are instrumental for further development of optimal, locally adapted algorithms for remote sensing of Chl in any type of natural waters.     

Atmospheric correction over case 2 waters with an iterative fitting algorithm

A modular atmospheric correction algorithm is proposed that uses atmospheric and water contents models to predict the visible and near-infrared reflectances observed by a satellite over water. These predicted values are compared with the satellite reflectances at each pixel, and the model parameters changed iteratively with an error minimization algorithm. The default atmospheric model uses single-scattering theory with a correction for multiple scattering based on lookup tables. With this model we used parameters of the proportions of three tropospheric aerosol types. For the default water content model we need the parameters of the concentrations of chlorophyll, inorganic sediment, and gelbstoff. The diffuse attenuation and backscatter coefficients attributed to these constituents are calculated and used to derive the water-leaving reflectance. Products include water-leaving reflectance, concentrations of water constituents, and aerosol optical depth and type. We demonstrate the application of the method to sea-viewing wide field-of-view sensor by using model data.     

Hyperspectral remote sensing for shallow waters. 2. Deriving bottom depths and water properties by optimization

In earlier studies of passive remote sensing of shallow-water bathymetry, bottom depths were usually derived by empirical regression. This approach provides rapid data processing, but it requires knowledge of a few true depths for the regression parameters to be determined, and it cannot reveal in-water constituents. In this study a newly developed hyperspectral, remote-sensing reflectance model for shallow water is applied to data from computer simulations and field measurements. In the process, a remote-sensing reflectance spectrum is modeled by a set of values of absorption, backscattering, bottom albedo, and bottom depth; then it is compared with the spectrum from measurements. The difference between the two spectral curves is minimized by adjusting the model values in a predictor-corrector scheme. No information in addition to the measured reflectance is required. When the difference reaches a minimum, or the set of variables is optimized, absorption coefficients and bottom depths along with other properties are derived simultaneously. For computer-simulated data at a wind speed of 5 m/s the retrieval error was 5.3% for depths ranging from 2.0 to 20.0 m and 7.0% for total absorption coefficients at 440 nm ranging from 0.04 to 0.24 m(-1). At a wind speed of 10 m/s the errors were 5.1% for depth and 6.3% for total absorption at 440 nm. For field data with depths ranging from 0.8 to 25.0 m the difference was 10.9% (R(2) = 0.96, N = 37) between inversion-derived and field-measured depth values and just 8.1% (N = 33) for depths greater than 2.0 m. These results suggest that the model and the method used in this study, which do not require in situ calibration measurements, perform very well in retrieving in-water optical properties and bottom depths from above-surface hyperspectral measurements.     

Aberration correction in an adaptive free-space optical interconnect with an error diffusion algorithm

Aberration correction within a free-space optical interconnect based on a spatial light modulator for beam steering and holographic wavefront correction is presented. The wavefront sensing technique is based on an extension of a modal wavefront sensor described by Neil et al. [J. Opt. Soc. Am. A 17, 1098 (2000)], which uses a diffractive element. In this analysis such a wavefront sensor is adapted with an error diffusion algorithm that yields a low reconstruction error and fast reconfigurability. Improvement of the beam propagation quality (Strehl ratio) for different channels across the input plane is achieved. However, due to the space invariancy of the system, a trade-off among the beam propagation quality for channels is obtained. Experimental results are presented and discussed.     

Accurate remote distance sensing by use of low-coherence interferometry: an industrial application

An apparatus for accurate remote distance sensing based on fiber-optic low-coherence light interferometry has been designed for molten glass level measurement. We demonstrate operation of the meter in an adverse industrial environment with <20-mum resolution (standard deviation) within a 20-mm range with the sensing head placed in an oven at ~800 degrees C. In laboratory conditions we were able to measure with 3-mum resolution, which could be improved to submicrometer level by optimization of a reference arm of the interferometer and detection electronics.     

一种快速匹配算法在遥感图像中的应用

针对相关匹配法计算量大的缺点提出了一种快速匹配算法。该算法采用由粗到精的匹配策略,对匹配区域先用环形模板进行粗匹配以确定待匹配窗口,再用全模板进行精匹配以确定正确匹配窗口。将该算法用于遥感图像匹配,仿真结果表明,该算法不仅能够实现正确匹配,而且计算量只有相关匹配法的10%。     

Atmospheric correction over case 2 waters with an iterative fitting algorithm: relative humidity effects

In algorithms for the atmospheric correction of visible and near-IR satellite observations of the Earth's surface, it is generally assumed that the spectral variation of aerosol optical depth is characterized by an Angstr?m power law or similar dependence. In an iterative fitting algorithm for atmospheric correction of ocean color imagery over case 2 waters, this assumption leads to an inability to retrieve the aerosol type and to the attribution to aerosol spectral variations of spectral effects actually caused by the water contents. An improvement to this algorithm is described in which the spectral variation of optical depth is calculated as a function of aerosol type and relative humidity, and an attempt is made to retrieve the relative humidity in addition to aerosol type. The aerosol is treated as a mixture of aerosol components (e.g., soot), rather than of aerosol types (e.g., urban). We demonstrate the improvement over the previous method by using simulated case 1 and case 2 sea-viewing wide field-of-view sensor data, although the retrieval of relative humidity was not successful.     

Control algorithm synthesis for a crystal oscillator and clock by the use of an adaptive state regulator

An optimal state regulator has been designed for a frequency-time stabilization system for the GLONASS/GPS reference synchronizing receiver, in which the controlled object is represented as an extended state-equation system. __________ Translated from Izmeritel’naya Tekhnika, No. 6, pp. 37–39, June, 2007.     

Line-pair selections for remote sensing of atmospheric ammonia by use of a coherent CO2 differential absorption lidar system

Research on wavelength selection of CO2 laser lines for range-resolved remote sensing of atmospheric ammonia by use of a coherent differential absorption lidar system is described. Four laser line pairs are suggested for different levels of ammonia concentrations from approximately a few parts per billion to 1 part per million in a polluted atmosphere. The most suitable line for measuring ambient ammonia concentrations is 9R(30), because it has the highest absorption coefficient. 10R(14) has the lowest absorption coefficient, making it suitable for strong source mapping. 10R(8) and 10P(32) are best for intermediate levels of ammonia concentration. Absorption coefficients of ammonia calculated from the HITRAN96 database are in good agreement (mostly within +/-10% )with other experimental results.Sensitivity of measurement, interference from water-vapor lines with typical humidity in the summer,and sensitivity of ammonia absorption cross section to temperature and pressure are analyzed and calculated for the four wavelength pairs. The results show that the interference from water-vapor lines is easily correctable to a negligible amount, and errors caused by uncertainties in temperature and pressure are insignificant.     

Large-scale wave-front reconstruction for adaptive optics systems by use of a recursive filtering algorithm

We propose a new recursive filtering algorithm for wave-front reconstruction in a large-scale adaptive optics system. An embedding step is used in this recursive filtering algorithm to permit fast methods to be used for wave-front reconstruction on an annular aperture. This embedding step can be used alone with a direct residual error updating procedure or used with the preconditioned conjugate-gradient method as a preconditioning step. We derive the Hudgin and Fried filters for spectral-domain filtering, using the eigenvalue decomposition method. Using Monte Carlo simulations, we compare the performance of discrete Fourier transform domain filtering, discrete cosine transform domain filtering, multigrid, and alternative-direction-implicit methods in the embedding step of the recursive filtering algorithm. We also simulate the performance of this recursive filtering in a closed-loop adaptive optics system.     

Modeling the optical properties of mineral particles suspended in seawater and their influence on ocean reflectance and chlorophyll estimation from remote sensing algorithms

The optical properties of mineral particles suspended in seawater were calculated from the Mie scattering theory for different size distributions and complex refractive indices of the particles. The ratio of the spectral backscattering coefficient to the sum of the spectral absorption and backscattering coefficients of seawater, b(b)(lambda)/[a(lambda) + b(b)(lambda)], was analyzed as a proxy for ocean reflectance for varying properties and concentrations of mineral particles. Given the plausible range of variability in the particle size distribution and the refractive index, the general parameterizations of the absorption and scattering properties of mineral particles and their effects on ocean reflectance in terms of particle mass concentration alone are inadequate. The variations in the particle size distribution and the refractive index must be taken into account. The errors in chlorophyll estimation obtained from the remote sensing algorithms that are due to the presence of mineral particles can be very large. For example, when the mineral concentration is 1 g m(-3) and the chlorophyll a concentration is low (0.05 mg m(-3)), current global algorithms based on a blue-to-green reflectance ratio can produce a chlorophyll overestimation ranging from approximately 50% to as much as 20-fold.     

Vertical attenuation coefficient of photosynthetically active radiation as a function of chlorophyll concentration and depth in case 1 waters

Based on empirical relations found in the literature, relatively simple mathematical models of the average of the total absorption of seawater [a(T(z,Chl))], the chlorophyll-specific absorption coefficient of phytoplankton [a*(ph(z,Chl))], and the backscattering coefficient [b(b(Chl))], weighted by the in situ spectral distribution of photosynthetically active scalar irradiance (PAR), as functions of chlorophyll concentration and depth, were developed. The models for a(T(z,Chl)) and b(b(Chl)) can be used to calculate the coefficient of vertical attenuation of PAR [K(o(z,Chl))] and therefore to estimate the vertical profile of PAR as an input to algorithms for primary production. One application of a*(ph(z,Chl)) may be in the correction of the initial slope of the photosynthesis-irradiance curve [alpha*((z))] for the in situ spectral distribution of PAR and the package effect. Also, a*(ph(z,Chl)) may be used to calculate phi((z)), the in situ quantum yield of photosynthesis, from phi(max) and irradiance.     

Lithographic characterization of the spherical error in an extreme-ultraviolet optic by use of a programmable pupil-fill illuminator

Extreme-ultraviolet (EUV) lithography remains a leading contender for use in the mass production of nanoelectronics at the 32 nm node. Great progress has been made in all areas of EUV lithography, including the crucial issue of fabrication of diffraction-limited optics. To gain an accurate understanding of the projection optic wavefront error in a completed lithography tool requires lithography-based aberration measurements; however, making such measurements in EUV systems can be challenging. We describe the quantitative lithographic measurement of spherical aberration in a 0.3 numerical aperture. EUV microfield optic. The measurement method is based on use of the unique properties of a programmable coherence illuminator. The results show the optic to have 1 nm rms spherical error, whereas interferometric measurements performed during the alignment of the optic indicated a spherical error of less than 0.1 nm rms.     

Improvement in sensing properties of SnO2 nanowires by functionalizing with Pt nanodots synthesized by gamma-ray radiolysis

Selectively-grown networked SnO2 nanowires were functionalized with Pt nanodots by the radiolysis process. NO2 sensing characteristics of Pt-functionalized SnO2 nanowires were compared with those of bare SnO2 nanowires. The results demonstrate that the Pt functionalization greatly enhances the sensitivity and response time in SnO2 nanowire-based gas sensors. The enhancement is likely to be associated with the spillover effect and/or easy dissociation of NO2 into more active chemical species by the catalytic effect of Pt.     

Optimization of the p-xylene oxidation process by a multi-objective differential evolution algorithm with adaptive parameters co-derived with the population-based incremental learning algorithm

Different operating conditions of p-xylene oxidation have different influences on the product, purified terephthalic acid. It is necessary to obtain the optimal combination of reaction conditions to ensure the quality of the products, cut down on consumption and increase revenues. A multi-objective differential evolution (MODE) algorithm co-evolved with the population-based incremental learning (PBIL) algorithm, called PBMODE, is proposed. The PBMODE algorithm was designed as a co-evolutionary system. Each individual has its own parameter individual, which is co-evolved by PBIL. PBIL uses statistical analysis to build a model based on the corresponding symbiotic individuals of the superior original individuals during the main evolutionary process. The results of simulations and statistical analysis indicate that the overall performance of the PBMODE algorithm is better than that of the compared algorithms and it can be used to optimize the operating conditions of the p-xylene oxidation process effectively and efficiently.     

溶胶-凝胶法制备CaAl_2SiO_6:Eu~(2+)荧光粉及其光学性质的研究

采用溶胶-凝胶法制备了CaAl2SiO6∶Eu2+荧光粉,利用X射线衍射仪、荧光光谱仪、热分析仪对其结构和光学性质进行了研究.结果表明,样品经1 000℃CaAl2SiO6∶Eu2+荧光粉在430 nm附近的发光峰为Eu2+中心的4f65d1(t2g)→4f7(8S7/2)跃迁;随Eu2+离子浓度的增加,样品的发光强度先增加后降低,在Eu2+浓度为0.7 mol%时达到最大;CaAl2SiO6∶Eu2+系列荧光粉的激发峰波长在280~390 nm之内,可以作为一种新型的UV-LED用三基色荧光粉.     

Radiative transfer model for the computation of radiance and polarization in an ocean-atmosphere system: polarization properties of suspended matter for remote sensing

A radiative transfer code termed OSOA for the ocean-atmosphere system that is able to predict the total and the polarized signals has been developed. The successive-orders-of-scattering method is used. The air-water interface is modeled as a planar mirror. Four components grouped by their optical properties, pure seawater, phytoplankton, nonchlorophyllose matter, and yellow substances, are included in the water column. Models are validated through comparisons with standard models. The numerical accuracy of the method is better than 2%; high computational efficiency is maintained. The model is used to study the influence of polarization on the detection of suspended matter. Polarizing properties of hydrosols are discussed: phytoplankton cells exhibit weak polarization and small inorganic particles, which are strong backscatterers, contribute appreciably to the polarized signal. Therefore the use of the polarized signal to extract the sediment signature promises good results. Also, polarized radiance could improve characterization of aerosols when open ocean waters are treated.     

Design of Compact Optical Bends with a Trench by use of Finite-Element and Beam-Propagation Methods

We address various approaches to the reduction of optical bending loss in photonic integrated circuits. Different methods, such as offsetting of waveguides and incorporation of the effect of an isolation trench on reduction of radiation loss, are demonstrated. A combination of the vectorial finite-element and the least-squares boundary residual methods is used to calculate transition losses and the required offset for their minimization. The semivectorial finite-element-based beam-propagation method is employed to calculate radiation loss. These vectorial approaches are also used to investigate several important properties, such as effects that are due to the sidewall slopes, rib heights, rib widths, and trench location, to optimize bend designs.