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We present a correction method of a systematic error that arises when total luminous flux of a large-area surface-emitting light source (SLS) is measured in an integrating sphere by substitution with a reference lamp. Putting a large-area SLS into an integrating sphere is equivalent to adding a low-reflective baffle to screen the spatial distribution of radiation inside the sphere, which severely changes the sphere responsivity. To compensate this self-screening effect, we propose to use a specially designed auxiliary lamp whose illuminating area is spatially matched to that of the SLS under test. The validity of the proposed correction method is tested by numerical simulations based on the radiative transfer equation. OCIS codes: 120.3150, 120.2040 120.5240.

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%. OCIS codes: 010.1290, 280.1100.

This paper addresses the problem of obtaining complete, detailed reconstructions of textureless shiny objects. We present an algorithm which uses silhouettes of the object, as well as images obtained under changing illumination conditions. In contrast with previous photometric stereo techniques, ours is not limited to a single viewpoint but produces accurate reconstructions in full 3D. A number of images of the object are obtained from multiple viewpoints, under varying lighting conditions. Starting from the silhouettes, the algorithm recovers camera motion and constructs the object's visual hull. This is then used to recover the illumination and initialize a multiview photometric stereo scheme to obtain a closed surface reconstruction. There are two main contributions in this paper: First, we describe a robust technique to estimate light directions and intensities and, second, we introduce a novel formulation of photometric stereo which combines multiple viewpoints and, hence, allows closed surface reconstructions. The algorithm has been implemented as a practical model acquisition system. Here, a quantitative evaluation of the algorithm on synthetic data is presented together with complete reconstructions of challenging real objects. Finally, we show experimentally how, even in the case of highly textured objects, this technique can greatly improve on correspondence-based multiview stereo results. Index Terms--Photometric stereo, multiple views, light calibration, silhouette.

This paper presents a framework to restore the 2D content printed on documents in the presence of geometric distortion and nonuniform illumination. Compared with text-based document imaging approaches that correct distortion to a level necessary to obtain sufficiently readable text or to facilitate optical character recognition (OCR), our work targets nontextual documents where the original printed content is desired. To achieve this goal, our framework acquires a 3D scan of the document's surface together with a high-resolution image. Conformal mapping is used to rectify geometric distortion by mapping the 3D surface back to a plane while minimizing angular distortion. This conformal "deskewing" assumes no parametric model of the document's surface and is suitable for arbitrary distortions. Illumination correction is performed by using the 3D shape to distinguish content gradient edges from illumination gradient edges in the high-resolution image. Integration is performed using only the content edges to obtain a reflectance image with significantly less illumination artifacts. This approach makes no assumptions about light sources and their positions. The results from the geometric and photometric correction are combined to produce the final output. Index Terms--Document restoration, geometric correction, shading correction, photometric correction, conformal mapping, document processing.

We present the results of photometric observations of trans-neptunian object 20000 Varuna, which were obtained during 7 nights in November 2004-February 2005. The analysis of new and available photometric observations of Varuna reveals a pronounced opposition surge at phase angles less than 0.1 deg with amplitude of 0.2 mag relatively to the extrapolation of the linear part of magnitude-phase dependence to zero phase angle. The opposition surge of Varuna is markedly different from that of dark asteroids while quite typical for moderate albedo Solar System bodies. We find an indication of variations of the scattering properties over Varuna's surface that could result in an increase of the lightcurve amplitude toward zero phase angle. It is shown that a similar phase effect can be responsible for lightcurve changes found for TNO 19308 (1996 T[O.sub.66]) in 1997-1999. Keywords: Trans-neptunian objects: Asteroids: Photometry

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.01.021 Byline: Amanda A.S. Gulbis (a), J.L. Elliot (a)(b)(c), Julia F. Kane (a) Keywords: Kuiper belt objects; Photometry Abstract: Recent dynamical analyses of the Kuiper belt have introduced a rigorous classification scheme, determined the mean orbital plane, and identified 'Core' and 'Halo' populations as a function of inclination with respect to this plane (Elliot, J.L., Kern, S.D., Clancy, K.B., Gulbis, A.A.S., Millis, R.L., Buie, M.W., Wasserman, L.H., Chiang, E.I., Jordan, A.B., Trilling, D.E., Meech, K.J., 2005. Astron. J. 129, 1117-1162). Here, we use new observations and existing data to investigate the colors of Kuiper belt objects (KBOs) within this framework. With respect to the bulk KBO color distribution (all objects for which we have B-V and V-R colors; median B-R=1.56), we find that the population of objects classified following (Elliot, J.L., Kern, S.D., Clancy, K.B., Gulbis, A.A.S., Millis, R.L., Buie, M.W., Wasserman, L.H., Chiang, E.I., Jordan, A.B., Trilling, D.E., Meech, K.J., 2005. Astron. J. 129, 1117-1162) as Classical tends to be red (B-R1.56) while the Scattered Near population is mostly neutral (B-R Author Affiliation: (a) Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA (b) Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA (c) Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff, AZ 86001, USA Article History: Received 29 October 2004; Revised 23 January 2006

The Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) can be used to obtain direct determination of the sizes and the albedos of asteroids. We present results of the first attempt to carry out interferometric observations of asteroids with the Mid Infrared Interferometric Instrument (MIDI) at the VLTI. Our target was 1459 Magnya. This is the only V-type asteroid known to exist in the outer main-belt, and its IRAS-albedo turns out to be rather low for an object of this taxonomic class. Interferometric fringes were not detected, very likely due to the fact that the flux emitted by the asteroid was lower than expected and below the MIDI threshold for fringe detection. However, by fitting the Standard Thermal Model to the N-band infrared flux measured by MIDI in photometric mode and to the visible absolute magnitude, obtained from quasi-simultaneous B- and V-band photometric observations, we have derived a geometric visible albedo of 0.37 [+ or -] 0.06 and an effective diameter of 17 [+ or -] 1 km. This new estimate of the albedo differs from that previously obtained by IRAS and is more consistent with the V-type taxonomic classification of 1459 Magnya. Keywords: Asteroids; Infrared observations; Photometry; Instrumentation

Six nights of R-band CCD observations of the classical Kuiper Belt Object (KBO) 20000 Varuna (2000 WR106) were obtained at the Palomar Mountain 60- and 200-in telescopes. The observations were scheduled to take advantage of a particularly favorable apparition which allowed us to sample down to extremely small solar phase angle ([alpha] = 0.036[degrees]). After rotational lightcurve subtraction, we found that the KBO exhibited a strong opposition surge of ~0.1 mag at phase angles [alpha] < 0.1[degrees]. We modeled our composite solar phase curve of Varuna using both H-G parameterization and Hapke theory and concluded that similar opposition surges may be wide spread among KBOs and that the regolith of Varuna may be significantly more porous than a typical main-belt C-type asteroid. Wide-spread opposition surges lead to higher albedos than derived assuming linear phase behavior: on the whole KBOs may be brighter than previously assumed. Keywords: Kuiper Belt Objects; Photometry

We present results of a ground-based observational study of the Hayabusa mission target near-Earth Asteroid (25143) Itokawa. Our data consist of BVRI-filter CCD photometry and low resolution CCD spectroscopy, from which the asteroid's rotation period, axial ratio, broadband colors, and taxonomic classification are derived. Analysis of the R-filter lightcurve data shows a synodic rotation period of 12.12 [+ or -] 0.02 h, consistent with results from other observers. We observed a maximum peak-to-peak amplitude of 1.05 magnitudes, which--depending on the taxonomic class assumed when correcting for phase angle effects--implies a minimum axial ratio of 2.14. The shape of the rotation lightcurves varies considerably between data sets due to the changing viewing geometry. The lightcurve data from this study has been included in the shape model analysis of Kaasalainen et al. (2003 Astron. Astrophys, 405, L29-L32) and the Hapke analysis of Lederer et al. (2005 Icarus 173,153-165). Color variations were also observed, with the interpolated color indices at lightcurve midpoint being: (B-V) = 0.94 [+ or -] 0.05, (V-R) = 0.40 [+ or -] 0.06, and (V-I) = 0.74 [+ or -] 0.07. Our low resolution Palomar spectra from March 2001 covered a wavelength range of 0.3-1.0 [micro]m. We measured a spectral slope of 9.3 [+ or -] 0.3%/100 nm between 0.55-0.70 [micro]m and a deep 1 um absorption (equivalent ECAS color: w-x = -0.111 [+ or -] 0.003, v-x = 0.031 [+ or -] 0.003). Comparison of our spectra with published ECAS data from Zellner et al. (1985 Icarus 61, 355416) indicates that this object is most likely of Q- or S-type, similar to ordinary chondrite meteorites. Our data are more consistent with a Q-type body when both the spectroscopic data and the available BVRI photometry are taken into account. Keywords: Near-Earth asteroids; Photometry; Spectroscopy; Hayabusa

A model based on geometrical optics has been developed to describe the photometric observations associated with a novel method to control the reflectance of a surface. In this new reflectance modulation approach, electrophoresis of pigment particles is used to absorb light reflected by total internal reflection (TIR). The pigment particles are sufficiently small that they substantially do not scatter light, but rather they modify the effective refractive index at the reflection interface. An incident light ray interacting with this modified effective index is attenuated in a spectrally selective manner. Although frustrated TIR has been understood and used in various applications for some time, in this case it is used to substantially modify the color of the reflected light, which to our knowledge has not been previously reported. A numerical model of the pigment particle distribution has been developed to describe the observations. OCIS codes: 260.0260, 260.6970.

We present analyses and results from both narrowband photometry and CCD imaging of Comet 81P/Wild 2 from multiple apparitions, obtained in support of the Stardust mission. These data include photometric measurements from 12 days before the encounter and imaging from 3 days after. Using narrowband photometry from the different apparitions, we analyzed the dust and gas production rates as a function of heliocentric distance, finding a substantial seasonal effect where the production of OH, NH, and dust peaks 11-12 weeks before perihelion. The CN, [C.sub.2], and [C.sub.3] production show no such asymmetry, suggesting that there may be heterogeneities among different sources on the nucleus. The water production peaked at a level of approximately 1.1 x [10.sup.28] molecule [s.sup.-1] in 1997. A comparison of the relative abundances of minor gas species places Wild 2 in the 'depleted' category in the A'Hearn et al. (1995, Icarus 118, 223) taxonomic classifications. Continuum measurements at multiple wavelengths indicate that the comet has a low dust-to-gas ratio, with moderately reddened dust. In our images we see a dust tail, an anti-tail and two well-defined jets. The primary jet, which persists for several months and is roughly aligned with the spin axis, has a source latitude > +75[degrees], while the secondary jet is located on the opposite hemisphere between -37[degrees] and -62[degrees]. We used the apparent position angle of the primary jet to determine the pole orientation, [alpha] = 281 [+ or -] 5[degrees], [sigma] = + 13 [+ or -] 7[degrees], and surmise that the nucleus is likely in a state of simple rotation. The primary source is continuously illuminated when Wild 2 is inbound and turns away from the Sun at about the time that the comet reaches perihelion, explaining the seasonal effects in the production rates. We measured lightcurves on several observing runs but saw no significant modulation, so no constraints can be set on the rotation rate. Images at different wavelengths show that the jets have the same colors as the dust in other regions in the coma and tail, indicating that the grain properties are similar throughout the coma. Radial profiles of the coma were measured in various directions on a number of different observing runs, and we discuss the findings from these measurements. Finally, we compare our results with other published data and attempt to predict future times at which observations should be obtained to help constrain additional properties. Keywords: Wild 2; Comets; Photometry; Composition; Rotational dynamics; Coma

Interpolation is often used to improve the accuracy of integrals over spectral data convolved with various response functions or power distributions. Formulae are developed for propagation of uncertainties through the […]

We propose a matrix method for the description of light reflection and transmission by an anisotropic multilayer system consisting of thin and thick layers. A method based on partial-wave matrix summations is applicable in the field of reflection and transmission photometry and ellipsometry. In the case of a thin anisotropic film, the interference effects were described by use of a coherent summation of Jones matrices. Incoherent intensity summations for a thick weakly anisotropic layer were characterized by use of the coherency vector formalism. Observable quantities or Mueller matrix components were obtained from the matrix describing transformation of the coherence vectors. OCIS codes: 260.1180, 260.1440, 260.2130, 313.6860, 120.2130.

We focus on the utility of rainbow schlieren as a tool for measuring the temperature of axisymmetric partially premixed flames (PPFs). Methane-air PPFs are established on a coannular burner. The flames involve two spatially distinct reaction zones, one in an inner premixed region that has a curved tip and a spatially planar wing portion and another that involves an outer nonpremixed zone in which intermediate species burn in air. Schlieren images are found to visualize clearly these PPF characteristics through light deflection by steep refractive-index gradients in the two reaction zone fronts. The temperature distributions of two flames established at fuel-rich mixture equivalence ratios of [[phi].sub.r] = 1.5 and 2.0, with bulk-averaged velocities, [V.sub.reac] = 60 cm [s.sup.-1] and [V.sub.air] = 50 cm [s.sup.-1], are inferred from color schlieren images, and a measurement error analysis is performed. Errors arise from two sources. One lies in the process of inferring the temperature from the refractive-index measurement by making assumptions regarding the local composition of the flame. We have shown through simulations that the average temperature deviations due to these assumptions are 1.7% for the [[phi].sub.r] = 1.5 flame and 2.3% for the [[phi].sub.r] = 2.0 flame. Another source involves the local uncertainty in the measurement of the transverse ray displacement at the filter plane that is used to determine the refractive index and thereafter the flame temperature. We have ascertained that a maximum error of 4.3% in the temperature determination can be attributed to this local measurement uncertainty. This investigation demonstrates the capability of the schlieren technique for providing not only qualitative displays of the PPFs but also full-field-of-view temperature measurements that are accurate, spatially resolved, and nonintrusive. OCIS codes: 280.1740, 120.6780, 280.2470, 120.5710.

The expression of the intensity of light reflected by the internal surface of an integrating sphere with an input power provided by a concentrated solar beam is established using a model of multiple reflection of photons. This intensity appears to be proportional to the input power, and thus makes viable the utilization of a photo-sensor interfaced with an integrating sphere to build a solar fluxmeter. The major parameters of the design of the fluxmeter are then identified, and an optimized design is proposed. An example of a practical instrument is given, and its performance is measured and discussed. The sensitivity of the fluxmeter to the spectral distribution of the solar radiation requires a careful calibration of the gauge in order to achieve a measurement error less than [+ or -] 5% of reading.

Modern photometer systems need to be accompanied by dosimeters that monitor exposure to total ionizing dose, ultraviolet light, and the flux of particles with linear energy transfer above some threshold value. These detectors should minimize space, weight, power, cost, and telemetry. A new approach is described in which single-chip, two-chip, or three-chips systems incorporated into the photometer's interface circuits measure the above while including information on the status of charge trapping in oxides and thermal noise at p-n junctions. Index Terms--AUTHOR: please supply your own keywords or send a blank e-mail to keywords@ieee.org to receive a list of suggested keywords.

The status of oxidation of oil and fat samples is normally judged by their peroxide value (PV), an index that seeks to determine the peroxide content by measuring how much iodine is liberated by the sample from iodide in an acidic medium in a specified time period. At peroxide levels of interest, not only does this approach require considerable analyst skill, the method is inherently flawed because of the considerable differences in the rates at which different peroxides liberate iodine from iodide and potentially also the consumption of nascent iodine by unsaturated sites. We propose here a substantially less biased method based on the oxidation of Fe(II) to Fe(III) by peroxides, followed by the colorimetric detection of the latter as the thiocyanate complex. The system is automated through flow injection photometry. A methanol-butanol mixed solvent is used as the carrier stream. Samples, generally prediluted in the same solvent, are injected into this carrier; streams bearing [Fe.sup.2-] and [SCN.sub.-] are separately introduced, mixed in-line, and merged with the carrier stream. After a reaction time of 30 s, the optical absorbance is detected by a light emitting diode (LED) based photometric detector. The method exhibits a wide dynamic range and good linearity (linear [r.sup.2], 0.9943 for 0.1-120 mequiv/kg cottonseed oil hydroperoxides) with a good throughput rate (up to 60 samples/h). The method was successfully applied to both vegetable (olive and cottonseed) oils and animal fats (lard and poultry fat).

Mach bands, the illusory brightness maxima and minima perceived at the initiation and termination of luminance gradients, respectively, are generally considered a direct perceptual manifestation of lateral inhibitory interactions among retinal or other lower order visual neurons. Here we examine an alternative explanation, namely that Mach bands arise as a consequence of real-world luminance gradients. In this first of two companion papers, we analyze the natural sources of luminance gradients, demonstrating that real-world gradients arising from curved surfaces are ordinarily adorned by photometric highlights and low-lights in the position of the illusory bands. The prevalence of such gradients provides an empirical basis for the generation of this perceptual phenomenon.

We compute the sign of Gaussian curvature using a purely geometric definition. Consider a point p on a smooth surface S and a closed curve y on S which encloses p. The image of [Gamma] on the unit normal Gaussian sphere is a new curve [Beta]. The Gaussian curvature at p is defined as the ratio of the area enclosed by [Gamma] over the area enclosed by [Beta] as [Gamma] contracts to p. The sign of Gaussian curvature at p is determined by the relative orientations of the closed curves [Gamma] and [Beta]. We directly compute the relative orientation of two such curves from intensity data. We employ three unknown illumination conditions to create a photometric scatter plot. This plot is in one-to-one correspondence with the subset of the unit Gaussian sphere containing the mutually illuminated surface normals. This permits direct computation of the sign of Gaussian curvature without the recovery of surface normals. Our method is albedo invariant. We assume diffuse reflectance, but the nature of the diffuse reflectance can be general and unknown. Error analysis on simulated images shows the accuracy of our technique. We also demonstrate the performance of this methodology on empirical data. Index Terms - Gaussian curvature, differential geometry, photometric invariant, photometric data, shape recovery, curve orientation.

A sensitive N[O.sub.2] analyzer, that uses a commercial LED emitting near 450 nm, has been developed. The prototype can measure N[O.sub.2] concentrations as low as 1 part in [10.sup.9] as defined by the Environmental Protection Agency. The response time of the system is 1 min. In addition, a demonstration of the use of external-cavity frequency-doubled diode laser radiation to accomplish similar measurements is reported. However, because of low nonlinear optical conversion efficiencies, comparable detection limits were not possible. Nonetheless, frequency-doubled diode-laser wavelengths have the potential to reach farther into the UV than LED technology, allowing the detection and measurement of numerous other gaseous species of interest.

The scientific motivation, design criteria, and specifications for a new ground-based instrument to observe the Sun in the He I 1083-nm spectral line is described. The instrument employs a liquid-crystal tunable Lyot-type spectral filter and an array detector that allows the full solar disk to be observed with a time cadence of minutes. We describe the telescope's optical and mechanical features and discuss computer interface and data-reduction procedures employed. Instrument performance during the initial year of operation of the telescope at its high-altitude site is summarized.

A simple light-scattering photometer has been designed to measure the angular distribution of the intensity of polarized laser light scattered by micrometer and submicrometer samples. The photometer uses an ellipsoidal reflector and simple optical components to collect the He-Ne laser-scattered light and to focus it onto a 512-element photodiode array. Experimental data have been obtained for several monodisperse aqueous solutions of latex spheres of different sizes. The results have been satisfactorily interpreted on the basis of the electromagnetic scattering theory. In particular the Mie formulation has been properly reformulated to take into account the corrections to the scattered intensity determined by the apparatus design making it possible to perform particle sizing.

We describe a simple visible-light stray-background-reducing baffle, suitable for use on a stabilized interplanetary platform. The design is a corrallike enclosure with five concentric walls. The baffle reduces direct sunlight and reflections from illuminated portions of the spacecraft by a factor of [10.sup.-12], provided that all these lie beyond at least a hemisphere centered on the viewing aperture. With this condition these bright sources do not directly illuminate within the outermost wall of the corral, and diffraction over the wall tops is the dominant mechanism by which light reaches the corral interior. We present design calculations for such a corral, as well as a laboratory measurement confirming the basic design assumption.

We present an original implementation of the absolute-sphere method recently proposed by Ohno. The luminous-flux unit, the lumen, is realized by means of an integrating sphere with an opening calibrated by a luminous-intensity standard placed outside. The adapted experimental setup permits one to measure luminous-flux values between 5 and 2500 lm with a significant improvement with respect to the simulated performances reported in the literature. Traditionally, the luminous-flux unit, the lumen, is realized by goniophotometric techniques in which the luminous-intensity distribution is measured and integrated over the whole solid angle. Thus sphere results are compared with those obtained with the Istituto Elettrotecnico Nazionale goniophotometer. In particular, a set of standards, characterized by luminous-flux values of [approximately]2000 lm, has been calibrated with both techniques. We highlight some of the problems encountered. Experimental results show that the agreement between the two methods is within the estimated uncertainty and suggest promising areas for future research. Key words: Calibration, goniophotometer, integrating sphere, lumen, luminous flux

A technique to compensate for gaseous absorption at near-infrared and infrared spectrum in solar extinction measurements obtained with two sun photometers is introduced. The procedure has been applied to optical depth measurements of aerosol, cloud and water vapor made during the International Satellite Cloud Climatology Project's Cirrus field experiments in Kansas from Nov. 13, 1991 to Dec. 7, 1991.

We report here a technique for determining the quantum throughput of a high-resolution, extreme-UV spectrometer by use of the National Institute of Standards and Technology's Synchroton Ultraviolet Radiation Facility at Gaithersburg, Md. (SURF-II). Observations were obtained at three different synchrotron operating energies with and without a magnesium fluoride filter and a tin-germanium filter. This calibration permits us to extract system efficiencies for three overlapping spectroscopic orders with uncertainties of 10-30%. The uncertainties quoted in this preliminary experiment were limited by the available time, and we propose that with minor refinements a significant improvement could be realized.

The sampling interval is an important parameter which must be chosen carefully, if measurements of the direct, global, and diffuse irradiance or illuminance are carried out to determine their averages over a given period. Using measurements from a day with rapidly moving clouds, we investigated the influence of the sampling interval on the uncertainty of the calculated 15-min averages. We conclude, for this averaging period, that the sampling interval should not exceed 60 s and 10 s for measurement of the diffuse and global components respectively, to reduce the influence of the sampling interval below 2%. For the direct component, even a 5 s sampling interval is too long to reach this influence level for days with extremely quickly changing insolation conditions.

Major League players were significantly more accurate in performing stereophotometry than were Minor League players. The stereophotometric data based upon the induction and extinction thresholds of the Pulfrich phenomenon were significantly correlated with the batting averages of Major League baseball players. The coefficient of determination, r squared, implies that visual ability as measured by stereophotometry accounts for 47% or more of the variation in batting averages of the Major League players. This test may be a useful index in predicting batting ability.

An ion exchange chromatographic separation technique utilizing a naphthalenedisulfonate-acetonitrile mobile phase with a cross-linked polymeric fluorocarbon-amine silica column can be used to extract C6-C12 aliphatic sulfonates and sulfates. The weak anion polymeric silica exchange column exhibits hydrophobicity which allows the isocratic elution of the aliphatic analytes. The indirect photometric and conductivity detection procedures applied to monitor the progress of the analytes have proven to be effective in detecting highly sensitive analytes with low detection limits.

A method is proposed in which the responsivity (A/lm) for the photometric quantity of a silicon photodiode, which is combined with a V([Lambda]) filter of a known spectral transmittance, can be directly self-calibrated by measuring the surface reflectance and the recombination losses of the photodiode for white light. The derived equation for this method assumes approximations that can cause systematic errors. A computer simulation was made to quantify these errors, and an accuracy of better than 0.2% was predicted. Although experimental validation is necessary, this method is promising as a new, practical method for high-accuracy photometric standards. Key words: Radiometry, photometry, photodetectors, silicon photodiodes, absolute responsivity, luminous intensity, luminous flux, self-calibration, photometric standards., A new method directly self-calibrates the photometric responsivity of a silicon photodiode combined with a V(lambda) filter by measuring the surface reflectance and the photodiode's recombination losses. The measurement does not require data on the photodiode's spectral absolute responsivity over the visible region when white light is used. The method is highly recommended for high-accuracy photometric standards, showing a 0.2% accuracy or better in a computer simulation to quantify systematic errors.

Abstract -- A new procedure is developed for the photometric determination of trace selenium in aqueous solutions. The selection of 2-(p-nitrophenyl)-3,5-diphenyltetrazolium chloride as a reagent for selenium is justified. The [...]

An imaging lens at f/4 is designed to have zoomlike variable chromatic and spherochromatic correction for imagery in each of the astronomical U, B, V, and R bands. Key words: Lens design, chromatic aberration, astronomy, photometry.

We present and discuss a novel mask design that provides multiwavelength measurement capability for the dayglow photometer.