Photometric Approach Research Articles

Robotic Monitoring of Gravitationally Lensed Quasars

We report on the first observational phase of the Liverpool Quasar Lens Monitoring (LQLM) project. This mainly consisted of the optical follow‐up of three lensed quasars using the 2 m Liverpool Robotic Telescope. The observational subprogram started in January 2005 and was completed in July 2007. We also describe our photometric approaches (including two pipelines to extract accurate and reliable fluxes of images of lensed quasars), the performance of the telescope when taking modest nightly exposures of lens systems, and the main scientific results from the observed light curves. The LQLM archive and the current status of the project (second phase) are also outlined.

A photometric approach for estimating normals and tangents

This paper presents a technique for acquiring the shape of real-world objects with complex isotropic and anisotropic reflectance. Our method estimates the local normal and tangent vectors at each pixel in a reference view from a sequence of images taken under varying point lighting. We show that for many real-world materials and a restricted set of light positions, the 2D slice of the BRDF obtained by fixing the local view direction is symmetric under reflections of the halfway vector across the normal-tangent and normal-binormal planes. Based on this analysis, we develop an optimization that estimates the local surface frame by identifying these planes of symmetry in the measured BRDF. As with other photometric methods, a key benefit of our approach is that the input is easy to acquire and is less sensitive to calibration errors than stereo or multi-view techniques. Unlike prior work, our approach allows estimating the surface tangent in the case of anisotropic reflectance. We confirm the accuracy and reliability of our approach with analytic and measured data, present several normal and tangent fields acquired with our technique, and demonstrate applications to appearance editing.

A Photometric Approach for Detection of Interaction of Cells with Their Ligands Based on Lectin Conjugated Gold Nanoparticles

A simple photometric approach for detection of interaction of lectins immobilized on colloidal gold particles with lymphocytes was demonstrated. It was shown that 20 nm gold particles conjugated with germ agglutinin or Concanavalin A undergo drastic optical changes upon interaction with lymphocytes. As a result of binding with cells, agglutination of gold-lectin-lymphocyte complex occurs with decrease of absorbance at 520 nm. This approach permitted to detect the interaction of 3000 lymphocytes/ml in 1.5 h without any additional procedures.

A model of the motion of the Nneuschwanstein bolide in the atmosphere

A new model of the atmospheric entry of the Neuschwanstein fireball has been developed. The fireball was photographed in Germany on April 6, 2002, and three fragments of it were found during a subsequent search in the territory predicted according to observations. In this study, the form of the meteoric body is assumed to be a cube with rounded vertices and edges. The estimated mass of the meteoric body at its entry into the atmosphere is close to the literature data obtained using seismic, acoustic, and infrasonic analysis. It is noted that the analysis of this fireball was for the first time made without using the photometric approach.

Helium stratification in HD145792: a new helium strong star

Abstract In this Letter, we report on the real nature of the star HD 145792, classified as He weak in ‘The General Catalogue of Ap and Am stars’. By means of FEROS@ESO 1.52m high-resolution spectroscopic data, we refined the atmospheric parameters of the star, obtaining: Teff= 14 400 ± 400 K, log g= 4.06 ± 0.08 and ξ= 0+0.6 km s−1. These values resulted always lower than those derived by different authors with pure photometric approaches. Using our values, we undertook an abundance analysis with the aim to derive, for the first time, the chemical pattern of the star's atmosphere. For metals, a pure local thermodynamic equilibrium synthesis (atlas9 and synthe) has been used, while for helium a hybrid approach has been preferred (atlas9 and synspec). The principal result of our study is that HD 145792 belongs to He-strong class contrary to the previous classification. Moreover, helium seems to be vertically stratified in the atmosphere, decreasing towards deepest layers. For what that concerns metal abundances, we found the following: overabundance of oxygen, neon, silicon, phosphorus, sulphur and calcium; carbon, nitrogen, magnesium, aluminum, titanium, chromium and nickel are normal, being the discrepancies from the solar values within the experimental errors; iron resulted to be slightly underabundant.

Entry mass for bolides of the Canadian network

Previously, the mass of meteor bodies was determined according to the so-called photometric formula by integration of the luminosity along the visible segment of the trajectory. On the other hand, the altitude and the meteor aerobraking rate in the atmosphere depend on the mass of the meteor body. In a number of papers, it was noted that the bolide masses estimated by the two indicated methods significantly differ from each other. For example, according to these data related to the bolides of both the European network and the US Prairie network, the photometric mass exceeds by an order of magnitude or more the mass determined by the aerobraking rate. In this study, we estimate the extraatmospheric meteor mass by choosing parameters that characterize the meteor aerobraking along the entire visible segment of the trajectory. The results for bolides of the Canadian network confirm once again the inadequacy of the photometric approach. In processing the observed-data, we widely exploit the conception of the photometric mass of a meteor body

Extra-atmospheric masses of the Canadian Network bolides

The extra-atmospheric masses of meteoric bodies have previously been determined using the so-called photometric formula, by integrating the luminosity along the visible portion of the trajectory. On the other hand, the mass of a meteoroid characterizes the braking height and intensity of the meteoroid in the atmosphere. Some studies note a substantial disagreement between the masses obtained in these two ways, using bolides of the European Bolide Network and of the US Prairie Network as examples. In nearly all cases, the photometric mass exceeds the mass determined from the braking intensity by an order of magnitude or more. Two explanations were suggested for this fact. According to one of them, a swarm of fragments, similar in size, rather than a single body is moving. This swarm brakes as an individual fragment, while it glows as a collection of fragments; i.e., it is much brighter than an individual fragment. The extra-atmospheric mass is determined here by properly fitting the parameters describing the braking of the meteor along the entire visible section of the trajectory. The results obtained for the bolides of the Canadian Network confirm again that the photometric approach is not tenable.

THE APPLICATION OF SCS+C METHODS FOR TOPOGRAPHIC RADIATION CORRECTION

As irradiance depends on slope and aspect,the remote sensing image in rugged areas is severely affected by the topographic effects.Topographic correction based on sun-canopy-sensor(SCS) geometry is more appropriate than terrain-based corrections in forest areas because SCS preserves the geotropic nature of trees(vertical growth) regardless of terrain,view,and illumination angles.However,in some terrain orientations,SCS might encounter the overcorrection problem similar to other simple photometric functions.To solve this problem,Scott proposes a new SCS+C correction that accounts for diffused atmospheric irradiance based on the C-correction.The SCS+C method was tested by a Landsat 5 image in a rugged area of Beijing.The results show that SCS+C can provide improved corrections compared with the SCS and three other photometric approaches(cosine,C,SCS),remove topographic effects successfully and restore the land-surface information in shadow areas effectively.

SCS+C: a modified Sun-canopy-sensor topographic correction in forested terrain

Topographic correction based on sun-canopy-sensor (SCS) geometry is more appropriate than terrain-based corrections in forested areas since SCS preserves the geotropic nature of trees (vertical growth) regardless of terrain, view, and illumination angles. However, in some terrain orientations, SCS experiences an overcorrection problem similar to other simple photometric functions. To address this problem, we propose a new SCS+C correction that accounts for diffuse atmospheric irradiance based on the C-correction. A rigorous, comprehensive, and flexible method for independent validation based on canopy geometric optical reflectance models is also introduced as an improvement over previous validation approaches, and forms a secondary contribution of this paper. Results for a full range of slopes, aspects, and crown closures showed SCS+C provided improved corrections compared to the SCS and four other photometric approaches (cosine, C, Minnaert, statistical-empirical) for a Rocky Mountain forest setting in western Canada. It was concluded that SCS+C should be considered for topographic correction of remote sensing imagery in forested terrain.

NewVRMagnification Ratios of QSO 0957+561

We present VR magnification ratios of QSO 0957+561 that are inferred from the GLITP light curves of Q0957+561A and new frames taken with the 2.56 m Nordic Optical Telescope about 14 months after the GLITP monitoring. To extract the fluxes of the two close components, two different photometric techniques are used, pho2comC and psfphot. From the two photometric approaches and a reasonable range for the time delay in the system (415-430 days), we do not obtain achromatic optical continuum ratios, but ratios depending on the wavelength. Our final global measurements ΔmAB(λV) = 0.077 ± 0.023 mag and ΔmAB(λR) = 0.022 ± 0.013 mag (1 σ intervals) are in agreement with the Oslo group results (using the same telescope in the same seasons but another photometric task and only one time delay of about 416 days). These new measurements are consistent with differential extinction in the lens galaxy, the Lyman limit system, the damped Lyα system, or the host galaxy of the QSO. The possible values for the differential extinction and the ratio of total to selective extinction in the V band are reasonable. Moreover, crude probability arguments suggest that the ray paths of the two components cross a similar dusty environment, including a network of compact dust clouds and compact dust voids. As an alternative (in fact, the usual interpretation of the old ratios), we also try to explain the new ratios as being caused by gravitational microlensing in the deflector. From magnification maps for each of the gravitationally lensed images, using different fractions of the surface mass density represented by the microlenses as well as different sizes and profiles of the V-band and R-band sources, several synthetic distributions of [ΔmAB(λV), ΔmAB(λR)] pairs are derived. In some gravitational scenarios, there is an apparent disagreement between the observed pair of ratios and the simulated distributions. However, several microlensing pictures work well. To decide between either extinction, microlensing, or a mixed scenario (extinction + microlensing), new observational and interpretation efforts are required.

The (un)resolved X‐ray background in the Lockman Hole

Most of the soft and a growing fraction of the harder X-ray background has been resolved into emission from point sources, yet the resolved fraction above 7 keV has only been poorly constrained. We use ∼700 ks of XMM-Newton observations of the Lockman Hole and a photometric approach to estimate the total flux attributable to resolved sources in a number of different energy bands. We find the resolved fraction of the X-ray background to be ∼90 per cent below 2 keV but it decreases rapidly at higher energies with the resolved fraction above ∼7 keV being only ∼50 per cent. The integrated X-ray spectrum from detected sources has a slope of r ∼ 1.75, much softer than the r = 1.4 of the total background spectrum. The unresolved background component has the spectral signature of highly obscured active galactic nuclei.

Geometric–photometric approach to monocular shape estimation

Monocular, reflectance map-based shape estimation has traditionally relied exclusively on photometric data, but the recently introduced disparity-based photometric stereo (DBPS) and Green's function shape from shading (GSFS) have brought more geometry into it by incorporating a matching equation, and can appropriately be termed a geometric–photometric approach. In DBPS, the matching equation is used for obtaining disparities from the input image pair, while in GSFS it is used for generating the matching image, a uniform disparity field being considered. In both cases, depth can be recovered if one assumes the disparities to result from the displacement of the irradiance pattern over the imaged surface. Starting from the analysis of such displacement under perspective projection, we show that the original DBPS/GSFS formulation must be amended: reconstructions with no free parameters are no longer feasible, but we are able to propose an approximate procedure which yields higher quality estimates, up to a multiplicative factor.

Design and analysis of spatially variant microlens-array diffuser with uniform illumination for short-range infrared wireless communications using photometric approach

A microlens-array was designed to transform the Gaussian radiation pattern of a point source to the uniform illumination in the far field, which can be used as an optical diffuser of short-range infrared wireless communication systems, allowing a transmitter to use more optical power safely. This paper describes how to design such a microlens-array diffuser and investigates the property of the light distribution generated thereby.

Photometric Calibrations after HIPPARCOS or: The Fine Structure of the HR-Diagram Revealed

AbstractThe Hipparcos parallaxes allow us to revisit photometric calibrations in terms of Mv and to evaluate the effects of the overall metallicity across the HR-diagram. For evolved stars the spread in mass remains the major and irreducible source of errors in the photometric Mv. If the relative locations of open cluster main-sequences are fully explained by the ∆Mv versus ∆[M/H] relation, the residual scatter in the lower main sequence appears due to additional parameters such as rotation or gravitational settling of the heavy elements. These cannot readily be studied by a purely photometric approach.

A step in quantifying the appearance of a lit scene

This paper presents the initial findings of an investigation into lighting appearance and the possibilities for its description using a photometric approach. The study shows that by describing the light pattern using the average luminance and the luminance distribution standard deviation of the most important area of the field of view, i.e. the horizontal 40° band, the acceptability of the Iighting appearance can be measured and calculated. Although this is still a simplistic approach, it provides a step towards better lighting installations, which could have benefits of comfort, productivity and energy efficiency as well as demonstrating a better understanding of the subject.

A photometric and spectroscopic study of the brightest northern Cepheids — II. Fundamental physical parameters

We present a new Cepheid reddening and effective temperature scale based on the uvby photometry published in the first paper of this series. Using all available information about the companion stars in Cepheids with bright blue secondaries, we remove their light from the observed light and colour curves. The resulting corrections are as large as 0.05–0.15 mag in several cases for different colour indices. A new photometric approach based on the (b − y) versus (B − V) two-colour diagram is tested with three other previous calibrations taken from the literature. Two uvby relations in earlier studies turn out to be the most reliable and consistent, and so they are used in deriving colour excesses. We determine systematically higher reddenings for Cepheids with a significant secondary light correction. The dereddened Strömgren colours are calibrated in terms of Teff and log g using the most recent synthetic colour grids. Our temperature scale is very close to that of Kraft, which is supported by other recent temperature determinations using the infrared flux method or Geneva photometry. The photometric gravities fit some of the earlier theoretical and observational (mainly spectroscopic) results very well.

Superoxide Radical Scavenging by Phenolic Bronchodilators under Aprotic and Aqueous Conditions

Asthmatic airway disease is accompanied by the appearance of inflammatory cells which produce reactive oxygen species (ROS). Therefore, the radical scavenging properties of the bronchodilators reproterol, fenoterol, salbutamol and terbutaline toward superoxide anion radicals and hydroperoxyl radicals were investigated in a model system by electron paramagnetic resonance spectroscopy (EPR) and photometric approaches. The substances under study showed activity in superoxide radical scavenging under aprotic and protic conditions as well. The efficiency of the reaction decreased in the order: fenoterol > salbutamol > reproterol > terbutaline > oxyfedrine when DMSO was used as an aprotic solvent. In an aqueous system, the rate constants decreased in the order: fenoterol > reproterol > salbutamol. It is suggested that the antioxidant effect of these β 2-agonists is an additional advantage in treatment of asthmatic lung disease, reducing the negative consequences of airway inflammation.

Route-Specific Cellular Expression of Cytochrome P4501A (CYP1A) in Fish (Fundulus heteroclitus) Following Exposure to Aqueous and Dietary Benzo[a]pyrene

Mummichog (Fundulus heteroclitus), an estuarine, teleost fish, were exposed for 456 hr to environmentally relevant concentrations of aqueous (10 μg/liter) and dietary (10 μg/g) benzo[a]pyrene (BP) in static renewal aquaria. Cellular expression of BP-inducible cytochrome P4501A (CYP1A) was evaluated several times during exposure by immunohistochemistry in longitudinal histologic sections of whole fish. CYP1A-associated staining intensities in tissues were scored by a subjective rating system similar to that used previously for qualitative information. Exposure to aqueous BP resulted in high levels of CYP1A-associated immunohistochemical staining in gill pillar cells, heart endothelium, and vascular endothelium. Exposure to dietary BP resulted in only mild to moderate staining in these tissues but high-intensity staining in gut mucosal epithelium. CYP1A induction in hepatocytes appeared most sensitive to aqueous exposure. Route-specific patterns of CYP1A expression were also observed in other cells including gill epithelia, pseudobranch, and skin. Expression of CYP1A in renal tubules and interrenal tissues was not affected by either treatment. Coexposure to both aqueous and dietary BP resulted in a pattern of induction reflecting both routes of exposure. In addition to the subjective rating system for scoring CYP1A expression, we developed a photometric approach that was used to obtain quantitative data on CYP1A-associated staining intensity. Photometric values of CYP1A staining intensity revealed patterns essentially the same as those observed during subjective ranking but were amenable to statistical analysis. The results of this study support the use of tissue-specific patterns of CYP1A expression in identification of target sites and exposure routes for polycyclic aromatic hydrocarbons and other compounds.

Integration of vision and laser displacement sensor for efficient and precise digitizing

This paper presents a new digitizing technique which integrates computer vision methods, such as the photometric stereo approach, with the laser displacement sensors (LDS). The curvature at each point of the surface can be measured cost-effectively by the photometric stereo approach. Once the information of curvature of the surface is provided, the measuring speed of LDS can be improved by digitizing at the selected points of the surface and meanwhile the accuracy of digitization is still maintained. By means of the integration, the merits of both approaches can be achieved simultaneously and the efficiency of the digitization can be improved. Experimental results are provided to verify the proposed method.

Evaluation of 4-amino-2-hydroxybenzoic acid as an eluent for indirect photometric determination of uncommon anions

The efficacity of 4-amino-2-hydroxybenzoic acids as an eluent for the separation and determination of uncommon anions has been evaluated. The intensely absorbing eluent (λmax 320 nm) offers a convenient indirect photometric approach to quantitate the species of interest in ppm and sub-ppm range. In the singlecolumn ion chromatography mode at 2 mM/2 mL/min and pH=6.0, clean separations of common and uncommon anions can be realized.