Photometric Model Research Articles

Photometric analysis of the nucleus of Comet 81P/Wild 2 from Stardust images

The disk-resolved flyby images of the nucleus of Comet 81P/Wild 2 collected by Stardust are used to perform a detailed study of the photometric properties of this cometary nucleus. A disk-integrated phase function from phase angle 11° to about 100° is measured and modeled. A phase slope of 0.0513 ± 0.0002 mag/deg is found, with a V-band absolute magnitude of 16.29 ± 0.02. Hapke’s photometric model yields a single-scattering albedo of 0.034, an asymmetry factor of phase function −0.53, a geometric albedo 0.059, and a V-band absolute magnitude of 16.03 ± 0.07. Disk-resolved photometric modeling from both the Hapke model and the Minnaert model results in 11% model RMS, indicating small photometric variations. The roughness parameter is modeled to be 27 ± 5° from limb-darkening profile. The modeled single-scattering albedo and asymmetry factor of the phase function are 0.038 ± 0.004 and −0.52 ± 0.04, respectively, consistent with those from disk-integrated phase function. The bulk photometric properties of the nucleus of Wild 2 are comparable with those of other cometary nuclei. The photometric variations on the surface of the nucleus of Wild 2 are at a level of or smaller than 15%, much smaller than those on the nucleus of Comet 19P/Borrelly and comparable or smaller than those on the nucleus of Comet 9P/Tempel 1. The similar photometric parameters of the nuclei of Wild 2, Tempel 1, and the non-source areas of fan jets on Borrelly may reflect the typical photometric properties of the weakly active surfaces on cometary nuclei.

Formation and detection of Earth mass planets around low mass stars

We investigate an in situ formation scenario for Earth-mass terrestrial planets in short-period, potentially habitable orbits around low-mass stars (M∗<0.3M⊙). We then investigate the feasibility of detecting these Earth-sized planets. We find that such objects can feasibly be detected by a ground-based transit survey if their formation frequency is high and if correlated noise can be controlled to sub-milli-magnitude levels. Our simulations of terrestrial planet formation follow the growth of planetary embryos in an annular region spanning 0.036 AU⩽a⩽0.4 AU around a fiducial M7 (0.12M⊙) primary. Initial distributions of planetary embryos are calculated using the semi-analytic evolutionary model outlined by Chambers [Chambers, J., 2006. Icarus 180, 496–513]. This model specifies how planetary embryos grow to the stage where the largest embryo masses lie in the 1024 g⩽Membryo⩽5×1026 g range (corresponding to the close of the so-called oligarchic growth phase). We then model the final phases of terrestrial planet assembly by allowing the embryos to interact with one another via a full N-body integration using the Mercury code. The final planetary system configurations produced in the simulations generally consist of 3–5 planets with masses of order 0.1–1.0M⊕ in or near the habitable zone of the star. We explore a range of disk masses (0.2M⊕ to 3.3M⊕) to illuminate the role disk mass plays in our results. With a high occurrence fraction or fortunate alignments, transits by the planet formed in our simulations could be marginally detected with modest telescopes of aperture 1 m or smaller around the nearest M-dwarf stars. To obtain a concrete estimate of the detectability of the planets arising in our simulations, we present a detailed Monte-Carlo transit detection simulation incorporating sky observability, local weather, a target list of around 200 nearby M-dwarfs, and a comprehensive photometric noise model. We adopt a baseline 1.5 mmag level of correlated stellar noise sampled from the photometry of the planet-bearing red dwarf Gl 436. With this noise model we find that detection of 1R⊕ planets around the local M-dwarfs is challenging for a ground-based photometric search, but that detection of planets of larger radius is a distinct possibility. The detection of Earth-sized planets is straightforward, however, with an all-sky survey by a low-cost satellite mission. Given a reduced correlated noise level of 0.45 mmag and an intermediate planetary ice-mass fraction of planets orbiting a target list drawn from the nearest late-type M dwarfs, a ground-based photometric search could detect, on average, 0.3 of these planets within two years and another 0.5 over an indefinitely extended search. A space-based photometric search (similar to the TESS mission) should discover ∼17 of these Earth-sized planets during its two year survey, with an assumed occurrence fraction of 28%.

Mutual occultations and eclipses of the Galilean satellites of Jupiter in 2002-2003: final astrometric results

The photometry of mutual occultations and eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by processing the light curves of the satellites observed during international campaigns of photometric observations of these mutual events. This work focuses on processing the complete data base of photometric observations of the mutual occultations and eclipses of the Galilean satellites made during the international campaign in 2002–2003. The final goal is to derive new accurate astrometric data. We propose the most accurate photometric model of mutual events based on all the data available to date about the satellites, and develop the corresponding method for extracting astrometric data. This method is applied to derive astrometric data from photometric observations of mutual occultations and eclipses of the Galilean satellites. We process the 371 light curves obtained during the international campaign of photometric observations of the Galilean satellites in 2002–2003. As compared with the theory, the rms ‘O-C’ residuals with respect to theory is equal to 0.055 and 0.064 arcsec in right ascension and declination, respectively, for the 274 best observations. Topocentric or heliocentric angular differences for satellite pairs are obtained for 119 time instants during the time period from 2002 October 10 to 2003 July 17.

Modelling the effects of dust evolution on the SEDs of galaxies of different morphological type

We present photometric evolution models of galaxies, in which, in addition to the stellar component, the effects of an evolving dusty interstellar medium have been included with particular care. Starting from the work of Calura et al., in which chemical evolution models have been used to study the evolution of both the gas and dust components of the interstellar medium in the solar neighbourhood, elliptical and irregular galaxies, it has been possible to combine these models with a spectrophotometric stellar code that includes dust reprocessing (grasil) to analyse the evolution of the spectral energy distributions (SEDs) of these galaxies. We test our models against observed SEDs both in the local universe and at high redshift, and use them to predict how the percentage of reprocessed starlight evolves for each type of galaxy. The importance of following the dust evolution is investigated by comparing our results with those obtained by adopting simple assumptions to treat this component.

投影仪相机显示系统的光度标定鲁棒方法

A novel photometric calibration framework is presented for a projector-camera (ProCam) display system, which is currently under booming development. Firstly, a piecewise bilinear model and five 5-ary color coding images are used to construct the homography between the image planes of a projector and a camera. Secondly, a photometric model is proposed to describe the data flow of the ProCam display system for displaying color images on colored surface in a general way. An efficient self-calibration algorithm is correspondingly put forward to recover the model parameters. Aiming to adapt this algorithm to different types of ProCam display system robustly, a 3\times7 masking coupling matrix and a patches image with 1024 color samples are adopted to fit the complex channel interference function of the display system. Finally, the experimental results demonstrate the validity and superiority of this calibration algorithm for the ProCam display system.

Binding of Recombinant but Not Endogenous Prion Protein to DNA Causes DNA Internalization and Expression in Mammalian Cells

Recombinant prion protein, rPrP, binds DNA. Both the KKRPK motif and the octapeptide repeat region of rPrP are essential for maximal binding. rPrP with pathogenic insertional mutations binds more DNA than wild-type rPrP. DNA promotes the aggregation of rPrP and protects its N terminus from proteinase K digestion. When rPrP is mixed with an expression plasmid and Ca(2+), the rPrP.DNA complex is taken up by mammalian cells leading to gene expression. In the presence of Ca(2+), rPrP by itself is also taken up by cells in a temperature- and pinocytosis-dependent manner. Cells do not take up rPrP(DeltaKKRPK), which lacks the KKRPK motif. Thus, rPrP is the carrier for DNA and the KKRPK motif is essential for its uptake. When mixed with DNA, a pentapeptide KKRPK, but not KKKKK, is sufficient for DNA internalization and expression. In contrast, whereas the normal cellular prion protein, PrP(C), on the cell surface can also internalize DNA, the imported DNA is not expressed. These findings may have relevance to the normal functions of PrP(C) and the pathogenic mechanisms of human prion disease.

Diffuse reflection in light-protective hoods

This paper discusses a photometric model of diffuse reflection in hoods with conical stops. A method of numerically solving the nonsteady-state integral equation of the self-irradiation field in the quasi-steady-state approximation and a method of organizing the cluster structure of the model are proposed.

The 2004 Las Campanas/Lowell Observatory campaign II. Surface properties of Hayabusa target Asteroid 25143 Itokawa inferred from Hapke modeling

Abstract We present an analysis of Hapke photometric modeling applied to uniform ground-based UBVRIJHK broadband data of asteroid 25143 Itokawa collected over a wide range of solar phase angles (4°–130°) during the 2004 apparition (Thomas-Osip et al., this issue, hereafter Paper I). Our photometric analyses indicate that Itokawa has a blocky surface with properties different from other, albeit larger, S-class asteroids studied using similar Hapke modeling analyses. Images from the Hayabusa spacecraft affirm the Hapke modeling results, demonstrating the ability of Hapke photometric modeling to predict a rocky asteroid surface correctly; this is the first time that a predicted rocky surface has been observed by a spacecraft. The single particle scattering functions are dominantly forward scattering, suggesting the surface material is composed primarily of clear particles whose scattering is dictated by the particle’s surface as opposed to internal scatterers (more typical of S-class asteroids), while the opposition parameters indicate that the regolith may be more compact than most of the limited number of asteroids visited by spacecraft to date. The roughness properties, single particle scattering properties, and opposition surge characteristics are all indicative of a surface where multiple scattering does not play a major role in defining the photometric properties of the regolith.

Near-infrared spectrophotometry of Asteroid 25143 Itokawa from NIRS on the Hayabusa spacecraft

A photometric analysis of the S-type Asteroid 25143 Itokawa is performed over multiple wavelengths ranging from 0.85 to 2.10 μm based on disk-resolved reflectance spectra obtained with the Hayabusa near-infrared spectrometer (NIRS). We derive the global photometric properties of Itokawa in terms of Hapke's photometric model. We find that Itokawa has a single-scatter albedo that is 35–40% less than that of Asteroid 433 Eros. Itokawa also has a single-particle phase function that is more strongly back-scattering than that of Eros. Despite its hummocky surface strewn with large boulders, Itokawa exhibits an opposition effect. However, the total amplitude of the opposition surge for Itokawa was estimated to be less than unity while Eros and other S-type asteroids have been found to have model values exceeding unity. The wavelength dependence of the opposition surge width reveals that coherent backscatter contributes to the opposition effect on Itokawa's surface. The photometric roughness of Itokawa is well constrained to a value of 26° ± 1° which is similar to Eros, suggesting that photometric roughness models the smallest surface roughness scale for which shadows exist.

Superresolution under Photometric Diversity of Images

Superresolution (SR) is a well-known technique to increase the quality of an image using multiple overlapping pictures of a scene. SR requires accurate registration of the images, both geometrically and photometrically. Most of the SR articles in the literature have considered geometric registration only, assuming that images are captured under the same photometric conditions. This is not necessarily true as external illumination conditions and/or camera parameters (such as exposure time, aperture size, and white balancing) may vary for different input images. Therefore, photometric modeling is a necessary task for superresolution. In this paper, we investigate superresolution image reconstruction when there is photometric variation among input images.

A test of the Hapke photometric model

We conducted a test of the Hapke (1981, 1984, 1986, 2002) photometric model to determine what physical parameters could be confidently linked to a surface's photometric behavior. The first author selected and measured the bidirectional reflectance distribution functions of 14 different samples in up to three different wavelengths using the Bloomsburg University Goniometer Laboratory. A total of 29 data files were obtained, each file containing more than 700 measurements from different viewing geometries; phase angles varied from 3° to 130°. The 29 files were initially sent “in‐the‐blind” to the second author, who was charged with inverting the data files and extracting best fit model parameters. Our baseline model used the most recent Hapke (2002) formulation with a two‐term Henyey‐Greenstein particle phase function and shadow‐hiding backscatter opposition effect (SHOE) model. We also inverted the data with three other variations that included three‐term Henyey‐Greenstein phase functions and both SHOE and the coherent backscatter opposition effect (CBOE) models. Our results were compared with the known physical properties of our samples. We found no compelling evidence that individual photometric parameters could be uniquely interpreted to reveal the physical state of our samples, either in an absolute or relative sense. Rather, combinations of physical properties such as albedo, roughness, and porosity were convolved within each retrieved photometric parameter. On the basis of our empirical evidence, we speculate that the fault lies with the inability of radiative transfer models to adequately account for discrete media and the effects of porosity, and its deficient assumption that individual particles are the primary scattering units.

Characterization of road microtexture by means of image analysis

Road surface microtexture (sub-millimeter scale) is essential for pavement skid-resistance. However, its measurement is only possible in the laboratory on cores taken from trafficked roads, and is time consuming. For efficient road monitoring, it is necessary to develop faster methods usable on-site. Collaboration has been developed for 2 years between LCPC and the laboratory Signal, Image and Communication (SIC) to develop a measurement and characterization method for road microtexture based on image analysis. This paper deals with too complementary works: • The measurement of road microtexture. Research is focused on the image measurement and extraction of roughness information from images. The prototype using a high-resolution camera is described. The procedure separating relief from aspect-information using a photometric model for the surface is given. Image-based relief variation is compared to relief variation obtained through a laser sensor. • The characterization of road microtexture. This characterization, obtained through a geometrical and frequential analysis of images, leads to descriptors related to the shape and the density of surface asperities. Experimental programmes were carried out to validate the feasibility of measuring on-site images and to correlate surface descriptors to friction. Results are presented and discussed. Perspective for future works is given.

Vision and Rain

The visual effects of rain are complex. Rain produces sharp intensity changes in images and videos that can severely impair the performance of outdoor vision systems. In this paper, we provide a comprehensive analysis of the visual effects of rain and the various factors that affect it. Based on this analysis, we develop efficient algorithms for handling rain in computer vision as well as for photorealistic rendering of rain in computer graphics. We first develop a photometric model that describes the intensities produced by individual rain streaks and a dynamic model that captures the spatio-temporal properties of rain. Together, these models describe the complete visual appearance of rain. Using these models, we develop a simple and effective post-processing algorithm for detection and removal of rain from videos. We show that our algorithm can distinguish rain from complex motion of scene objects and other time-varying textures. We then extend our analysis by studying how various factors such as camera parameters, rain properties and scene brightness affect the appearance of rain. We show that the unique physical properties of rain--its small size, high velocity and spatial distribution--makes its visibility depend strongly on camera parameters. This dependence is used to reduce the visibility of rain during image acquisition by judiciously selecting camera parameters. Conversely, camera parameters can also be chosen to enhance the visibility of rain. This ability can be used to develop an inexpensive and portable camera-based rain gauge that provides instantaneous rain-rate measurements. Finally, we develop a rain streak appearance model that accounts for the rapid shape distortions (i.e. oscillations) that a raindrop undergoes as it falls. We show that modeling these distortions allows us to faithfully render the complex intensity patterns that are visible in the case of raindrops that are close to the camera.

Photometric analysis and disk-resolved thermal modeling of Comet 19P/Borrelly from Deep Space 1 data

Images returned from the Deep Space 1 (DS-1) spacecraft during its encounter with Comet 19P/Borrelly are used to study its disk-integrated and disk-resolved photometry and its thermal properties. A disk-integrated phase function was constructed from a combination of DS-1 images and ground-based observations, giving a geometric albedo of 0.072 ± 0.020 and a phase slope of 0.043 mag deg −1. The shape model of Borrelly [Kirk, R.L., Howington-Kraus, E., Soderblom, L.A., Giese, B., Oberst, J., 2004a. Icarus 167, 54–69] and the ephemerides of DS-1 were used to analyze the disk-resolved photometric data with Hapke's theoretical model. It was found that the surface of Borrelly displays large photometric heterogeneities in its photometric parameters. The single-scattering albedo, w, varies by a factor of 2.5 with an average of 0.057 ± 0.009 ; the asymmetry factor, g, ranges from almost isotropic (−0.1) to strongly backscattering (−0.7) with an average of − 0.43 ± 0.07 ; the roughness parameter, θ ¯ , is less than 35° for most parts of surface but ranges up to 55° in some areas. Its average is 22 ° ± 5 ° . The observed 1-D temperature profile is modeled well by the standard thermal model (STM) for inactive regions and is found to be consistent with a very low thermal inertia. Water sublimation in the source region of the fan jet is observed to decrease the surface temperature from the STM predictions by 20–40 K. The source areas of two collimated jets could not be determined from either photometric model or thermal model. It is evident that the fan jet activity occurring on Borrelly's surface can be correlated to areas of relatively high albedo, weak backscattering, and high roughness.

Photometry and polarimetry of particulate surfaces and aerosol particles over a wide range of phase angles

We present results of photometric and polarimetric laboratory measurements of particulate surfaces undergoing different degrees of compression and aerosol particles at a phase angle range from 7 to 150°. Nine samples of natural materials with different albedo and particle sizes were measured in red ( λ=0.63 μm) and blue ( λ=0.44 μm) light using two different instruments: Kharkov's large-phase-angle photopolarimeter for measurements of surfaces and Amsterdam's polar nephelometer for particles in air. We compare phase curves for particulate surfaces with the corresponding measurements for single particles. Our measurements suggest that the maximum of positive polarization, which is observed for particulate surfaces at large phase angles, is mainly due to the contribution of single-particle scattering. We observe an increase in the polarization degree at large phase angles with increased sample compression. We have found the negative polarization at small phase angles to be strengthened sharply by surface compression. This is partially a geometric effect at slanting view (70°), which is explained via double scattering. For photometric data, we carried out a comparison between experimental data and the Hapke photometric model. The comparison of measured photometric phase-angle dependencies with the model reveals several model shortcomings. The principle shortcoming is the spectral dependence of the model parameters that should be independent of wavelength.

On the relationship between visual magnitudes and gas and dust production rates in target comets to space missions

In this paper, we report the results of a cometary research, developed during the last 10 years by us, involving a criterious analysis of gas and dust production rates in comets directly associated to recent space missions. For the determination of the water release rates we use the framework of the semi-empirical model of observed visual magnitudes [Newburn Jr., R.L. A semi-empirical photometric theory of cometary gas and dust production. Application to P/Halley’s production rates, ESA–SP 174, 3, 1981; de Almeida, A.A., Singh, P.D., Huebner, W.F. Water release rates, active areas, and minimum nuclear radius derived from visual magnitudes of comets – an application to Comet 46P/Wirtanen, Planet. Space Sci. 45, 681–692, 1997; Sanzovo, G.C., de Almeida, A.A., Misra, A. et al. Mass-loss rates, dust particle sizes, nuclear active areas and minimum nuclear radii of target comets for missions STARDUST and CONTOUR, MNRAS 326, 852–868, 2001.], which once obtained, were directly converted into gas production rates. In turn, the dust release rates were obtained using the photometric model for dust particles [Newburn Jr., R.L., Spinrad, H. Spectrophotometry of seventeen comets. II – the continuum, AJ 90, 2591–2608, 1985; de Freitas Pacheco, J.A., Landaberry, S.J.C., Singh, P.D. Spectrophotometric observations of the Comet Halley during the 1985–86 apparition, MNRAS 235, 457–464, 1988; Sanzovo, G.C., Singh, P.D., Huebner, W.F. Dust colors, dust release rates, and dust-to-gas ratios in the comae of six comets, A&AS 120, 301–311, 1996.]. We applied these models to seven target comets, chosen for space missions of “fly-by”/impact and rendezvous/landing.

Markov Chain Monte Carlo Methods Applied to Photometric Spot Modeling

ABSTRACTI demonstrate that Markov chain Monte Carlo methods can be used very effectively to determine best‐fit values, uncertainties, and possible correlations or degeneracies in the fitted parameters of photometric spot modeling. Details of the Markov chain Monte Carlo methods applied here are briefly described, including the Metropolis‐Hastings algorithm and the tests that are used to ensure proper convergence and mixing. This Markov chain Monte Carlo functionality is applied to recent observations of ϵ Eridani by the Microvariablity and Oscillations of Stars (MOST) satellite, and the two‐spot solution showing differential rotation, as discussed in B. Croll et al. Conclusions in the latter are largely confirmed, but a strong correlation between the inclination and other fitted parameters is noted. The Markov chain Monte Carlo functionality has been included in StarSpotz, a freely available program for photometric spot modeling.

Shape, size and multiplicity of main-belt asteroids: I. Keck Adaptive Optics survey

This paper presents results from a high spatial resolution survey of 33 main-belt asteroids with diameters >40 km using the Keck II Adaptive Optics (AO) facility. Five of these (45 Eugenia, 87 Sylvia, 107 Camilla, 121 Hermione, 130 Elektra) were confirmed to have satellite. Assuming the same albedo as the primary, these moonlets are relatively small (∼5% of the primary size) suggesting that they are fragments captured after a disruptive collision of a parent body or captured ejecta due to an impact. For each asteroid, we have estimated the minimum size of a moonlet that can positively detected within the Hill sphere of the system by estimating and modeling a 2- σ detection profile: in average on the data set, a moonlet located at 2 / 100 × R Hill ( 1 / 4 × R Hill ) with a diameter larger than 6 km (4 km) would have been unambiguously seen. The apparent size and shape of each asteroid was estimated after deconvolution using a new algorithm called AIDA. The mean diameter for the majority of asteroids is in good agreement with IRAS radiometric measurements, though for asteroids with a D < 200 km , it is underestimated on average by 6–8%. Most asteroids had a size ratio that was very close to those determined by lightcurve measurements. One observation of 104 Klymene suggests it has a bifurcated shape. The bi-lobed shape of 121 Hermione described in Marchis et al. [Marchis, F., Hestroffer, D., Descamps, P., Berthier, J., Laver, C., de Pater, I., 2005c. Icarus 178, 450–464] was confirmed after deconvolution. The ratio of contact binaries in our survey, which is limited to asteroids larger than 40 km, is surprisingly high (∼6%), suggesting that a non-single configuration is common in the main-belt. Several asteroids have been analyzed with lightcurve inversions. We compared lightcurve inversion models for plane-of-sky predictions with the observed images (9 Metis, 52 Europa, 87 Sylvia, 130 Elektra, 192 Nausikaa, and 423 Diotima, 511 Davida). The AO images allowed us to determine a unique photometric mirror pole solution, which is normally ambiguous for asteroids moving close to the plane of the ecliptic (e.g., 192 Nausikaa and 52 Europa). The photometric inversion models agree well with the AO images, thus confirming the validity of both the lightcurve inversion method and the AO image reduction technique.

Astrometric results of observations of mutual occultations and eclipses of the Galilean satellites of Jupiter in 2003

Context. The photometry of mutual occultations and the eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by analyzing the light curves of the satellites observed during these mutual events. Aims. The final goal of observations is to refine the models of motion for the natural satellites, and to develop a very accurate photometric model of mutual occultations and eclipses of satellites. This paper is focusing on the differences of topocentric or heliocentric coordinates of satellites pairs by analyzing the photometry of mutual occultations and the eclipses of natural satellites. Methods. We propose the most accurate photometric model of mutual events to date based on all available data about the satellites, and have developed the corresponding method for extracting astrometric data. We analyze the errors of astrometric results obtained in terms of different scattering laws allowing for reflecting properties of the satellites surfaces. In addition we consider how to allow various previously neglected effects. Results. We describe the results obtained by applying our method to observations of mutual occultations and eclipses of the Galilean satellites of Jupiter made in 2002–2003. We show that the coordinate errors due to irreducible systematic errors of photometry are about the same as the errors introduced by neglecting the above effects. We find the available maps of satellites surfaces to be unsuitable for deriving photometric event models.

Toward a CIE supplementary system of photometry: brightness at any level including mesopic vision

Photometry for brightness at any level including mesopic vision is described on the basis of the work conducted towards the development of a Commission Internationale de l'Eclairage (CIE) supplementary system of photometry in CIE technical committees. Several critical items in developing such a system are discussed: (1) how to scale brightness using the concept of equivalent luminance; (2) the basic vision model of brightness perception; (3) a description of the chromatic contribution to brightness at the photopic as well as at the mesopic level; (4) formulation of an adaptation coefficient for rod-cone interaction. A possible photometric model for brightness is described based on these considerations, together with a quantitative evaluation of the model using experimental data.