Transferring the calibration of direct solar irradiance to diffuse-sky radiance measurements for CIMEL Sun-sky radiometers

Two types of sunphotometric measurement are considered in this study: direct-Sun irradiance and diffuse-sky radiance. Based on CIMEL CE318 Sun-sky radiometer characteristics, we introduce a gain-corrected solid angle that allows interconverting calibration coefficients of these two types of measurement, thus realizing a "vicarious" radiance calibration. The accuracy of the gain-corrected solid angle depends on the number of available historical calibration records. The method is easy to use, provided that at least one laboratory calibration has been made previously. Examples coming from three distinct CE318 versions belonging to the AERONET/PHOTONS network are presented to provide details on the vicarious calibration method and protocols. From the error propagation analysis and the comparison with laboratory results, the uncertainty of the vicarious radiance calibration is shown to be comparable with the laboratory one, e.g., 3%-5%.     

Design of an aspherical lens to generate a homogenous irradiance for three-dimensional sensors with a light-emitting-diode source

A design of a large-numerical-aperture aspherical singlet for three-dimensional (3-D) sensor applications is presented. This lens can be used to generate a homogenous irradiance on the target in a 3-D sensor, which is based on the principle of time of flight and uses an LED as light source. A numerical method was used in the design. The designed planoaspherical singlet has a numerical aperture of 0.67, low refractive index, and moderate surface shape for easy fabrication. The simulation results revealed that the irradiance deviation within 97% of the designed area is less than 5% and that the transmittance of the lens is greater than 90.5%. The results from a Lambertian source were compared with those from a point source.     

Long-term temporal stability of the National Institute of Standards and Technology spectral irradiance scale determined with absolute filter radiometers

The temporal stability of the National Institute of Standards and Technology (NIST) spectral irradiance scale as measured with broadband filter radiometers calibrated for absolute spectral irradiance responsivity is described. The working standard free-electron laser (FEL) lamps and the check standard FEL lamps have been monitored with radiometers in the ultraviolet and the visible wavelength regions. The measurements made with these two radiometers reveal that the NIST spectral irradiance scale as compared with an absolute thermodynamic scale has not changed by more than 1.5% in the visible from 1993 to 1999. Similar measurements in the ultraviolet reveal that the corresponding change is less than 1.5% from 1995 to 1999. Furthermore, a check of the spectral irradiance scale by six different filter radiometers calibrated for absolute spectral irradiance responsivity based on the high-accuracy cryogenic radiometer shows that the agreement between the present scale and the detector-based scale is better than 1.3% throughout the visible to the near-infrared wavelength region. These results validate the assigned spectral irradiance of the widely disseminated NIST or NIST-traceable standard sources.     

Celestial body irradiance determination from an underfilled satellite radiometer: application to albedo and thermal emission measurements of the Moon using CERES

The Clouds and the Earth's Radiant Energy System (CERES) is a program that measures the Earth radiation budget (ERB) from two polar orbiting satellite platforms. CERES radiometers are designed to make stable broadband measurements of scattered solar and emitted thermal radiative flux leaving Earth with an accuracy of 1% or better. Using versatile and programmable scan modes, it is also possible for every CERES instrument to view the Moon on each orbit. However, until now, it has not been possible to derive absolute measurements of lunar irradiance using CERES because the Moon's disk fills only 10% of the telescope field of view. This work presents a method of integrating CERES raster-scan data in order to obtain a measurement of the average scattered solar and emitted thermal radiance from the entire lunar disk. The technique results in excellent agreement between CERES instruments on different satellites as to lunar albedo and emitted thermal flux. The average broadband Moon albedo is measured by CERES at a value of 0.1362 (+/-2-3%) when normalized to a static lunar phase angle of 7 degrees using the U.S. Geological Survey lunar irradiance Robotic Lunar Observatory model. The method for the first time also yields very accurate measurements of the thermal irradiance emitted from the Moon. These suggest an average long-wave flux of 977 Wm(-2) (+/-2-3% at 7 degrees phase), implying an approximate mean surface temperature of around 92 degrees C. Statistical analysis on available data suggests that a CERES instrument performing monthly lunar measurements could utilize the Moon as a stability target and reduce calibration drifts to 0.3% per decade or less within an instrument's lifetime. Given the success of the technique, a solar calibration system is proposed that will allow precise tracking of an ERB instrument's optical degradation using the Sun.     

Reduction of nonlinear dynamic systems with an application to signal transduction pathways

Mathematical modelling of kinetic processes with different time scales allows a reduction of the governing equations using quasi-steady-state approximations (QSSA). A QSSA theorem is applied to a mathematical model of the influence that Raf kinase inhibitor protein (RKIP) has on the ERK signalling pathway. On the basis of previously published parameter values, the system of 11 ordinary differential equations is rewritten in a form suitable for model reduction. In accordance with the terminology of the QSSA theorem, it is established that four of the protein and protein-complex concentrations are `fast varying', such that the corresponding kinetic equations form an attached system. Another concentration is `medium varying' such that the corresponding equation is reduced with respect to the four fast ones. The other six concentrations are `slow varying', which means the corresponding kinetic equations also present a reduced system with respect to the others. Analytical solutions, relating the steady-state values of the fast varying protein concentrations and the slow varying ones, are derived and interpreted as restrictions on the regulatory role of RKIP on ERK-pathway     

Use of a Spectralon panel to measure the downwelling irradiance signal: case studies and recommendations

Field determinations of the remote sensing reflectance signal are necessary to validate ocean color satellite sensors. The measurement of the above-water downwelling irradiance signal Ed(0+) is commonly made with a reference plaque of a known reflectance. The radiance reflected by the plaque (L(dspec)) can be used to determine Ed(0+) if the plaque is assumed to be near Lambertian. To test this assumption, basic experiments were conducted on a boat under changing sky conditions (clear, cloudy, covered) and with different configurations for simultaneous measurements of L(dspec) and Ed(0+). For all measurement configurations, results were satisfactory under a clear sky. Under cloudy or covered skies, shadow effects on the plaque induced errors up to 100% in the determination of Ed(0+). An appropriate measurement configuration was defined, which enabled Ed(0+) to be determined with an accuracy of better than +/- 15% regardless of the sky conditions.     

Cryogenic low acoustic loss bonding of niobium with application to gravitational radiation detectors

Ultralow acoustic loss mechanical resonators are required for gravitational radiation detectors and other low noise mechanical systems. Experimental design often involves the joining of two or more components, but problems of making low acoustic loss joints has restricted design in this area. Here we show that low acoustic loss niobium components can be bonded.     

Statistics of the radio-frequency signal based on K distribution with application to echocardiography

We study in this paper the statistics of the radio frequency (RF) signal in the case of partially developed speckle. Using the K distribution framework, we give the probability density function of the associated distribution, the corresponding moments, and estimators for the parameters of the distribution. The consistency of the proposed estimators is evaluated in terms of their bias and variance through numerical simulations. The ability of the proposed distribution to model RF echographic signals from cardiac tissues is evaluated from data acquired in vivo.     

A technique for the evaluation of signal enhancement with application to gamma ray spectra

A procedure is presented which permits the quantitative evaluation of deconvolution algorithms with regard to their ability to enhance or improve the resolution of spectral signals. The approach used here revealed that the maximum realizable enhancement can be expressed in terms of a single variable which is a function of response width, peak area, background level and nearest neighbour spacing. The evaluation procedure was designed primarily to test nonlinear algorithms, a class which can ensure positivity of solution and thereby control noise growth in the recovery process. The effects of response width, system gain, background level and proximity of nearest neighbours are addressed and the utility of the test is demonstrated by evaluation of specific algorithms.     

Determining moisture content of wheat with an artificial neuralnetwork from microwave transmission measurements

An artificial neural network (ANN) was used to determine the moisture content of hard, red winter wheat. The ANN was trained to recognize moisture content in the range from 10.6% to 19.2% (wet basis) from transmission coefficient measurements on samples of wheat. The measurements were made at 8 microwave frequencies (10 GHz to 18 GHz) on wheat samples of varying bulk densities (0.72 g/cm³ to 0.88 g/cm³) at 24°C. The trained network predicted moisture content (%) with a mean absolute error of 0.135 (compared with oven-dried measurements)     

Novel application of red-light runner proneness theory within traffic microsimulation to an actual signal junction

Building on previous research a conceptual framework, based on potential conflicts analysis, has provided a quantitative evaluation of ‘proneness’ to red-light running behaviour at urban signalised intersections of different geometric, flow and driver characteristics. The results provided evidence that commonly used violation rates could cause inappropriate evaluation of the extent of the red-light running phenomenon. Initially, an in-depth investigation of the functional form of the mathematical relationship between the potential and actual red-light runners was carried out. The application of the conceptual framework was tested on a signalised intersection in order to quantify the proneness to red-light running. For the particular junction studied proneness for daytime was found to be 0.17 north and 0.16 south for opposing main road approaches and 0.42 east and 0.59 west for the secondary approaches. Further investigations were carried out using a traffic microsimulation model, to explore those geometric features and traffic volumes (arrival patterns at the stop-line) that significantly affect red-light running. In this way the prediction capability of the proposed potential conflict model was improved. A degree of consistency in the measured and simulated red-light running was observed and the conceptual framework was tested through a sensitivity analysis applied to different stop-line positions and traffic volume variations. The microsimulation, although at its early stages of development, has shown promise in its ability to model unintentional red light running behaviour and following further work through application to other junctions, potentially provides a tool for evaluation of alternative junction designs on proneness. In brief, this paper proposes and applies a novel approach to model red-light running using a microsimulation and demonstrates consistency with the observed and theoretical results.     

外加周期信号控制下的随机共振及其应用

分析了双稳系统的Kramers逃逸率与外加周期信号参数的关系,揭示了外加周期信号通过调节Kramers逃逸率影响微弱周期信号的随机共振效应,从而人为地产生或增强随机共振,实现随机共振的有效控制.数值仿真和实验结果表明,外加周期信号控制下的随机共振,可以增强双稳系统输出功率谱在微弱周期信号频率处的谱值,检测出强噪声中的微弱信号,在涡街频率检测方面的应用是可行和有效的.     

Low temperature acoustic loss of pure and alloyed niobium and titanium with application to gravitational radiation detectors

Low acoustic loss cryogenic materials are required for various high precision experiments, resonant-bar gravitational radiation antennae in particular. We report here cryogenic acoustic loss measurements of various commercially pure and alloyed Nb and Ti samples.