Monochromatic Approach Research Articles

RAINBOW: A colorful approach to multipassband light-curve estimation

Context. Time series generated by repeatedly observing astronomical transients are generally sparse, irregularly sampled, noisy, and multidimensional (obtained through a set of broad-band filters). In order to fully exploit their scientific potential, it is necessary to use this incomplete information to estimate a continuous light-curve behavior. Traditional approaches use ad hoc functional forms to approximate the light curve in each filter independently (hereafter, the MONOCHROMATIC method). Aims. We present RAINBOW, a physically motivated framework that enables simultaneous multiband light-curve fitting. It allows the user to construct a 2D continuous surface across wavelength and time, even when the number of observations in each filter is significantly limited. Methods. Assuming the electromagnetic radiation emission from the transient can be approximated by a blackbody, we combined an expected temperature evolution and a parametric function describing its bolometric light curve. These three ingredients allow the information available in one passband to guide the reconstruction in the others, thus enabling a proper use of multisurvey data. We demonstrate the effectiveness of our method by applying it to simulated data from the Photometric LSST Astronomical Time-series Classification Challenge (PLAsTiCC) as well as to real data from the Young Supernova Experiment (YSE DR1). Results. We evaluate the quality of the estimated light curves according to three different tests: goodness of fit, peak-time prediction, and ability to transfer information to machine-learning (ML) based classifiers. The results confirm that RAINBOW leads to an equivalent goodness of fit (supernovae II) or to a goodness of fit that is better by up to 75% (supernovae Ibc) than the MONOCHROMATIC approach. Similarly, the accuracy improves for all classes in our sample when the RAINBOW best-fit values are used as a parameter space in a multiclass ML classification. Conclusions. Our approach enables a straightforward light-curve estimation for objects with observations in multiple filters and from multiple experiments. It is particularly well suited when the light-curve sampling is sparse. We demonstrate its potential for characterizing supernova-like events here, but the same approach can be used for other classes by changing the function describing the light-curve behavior and temperature representation. In the context of the upcoming large-scale sky surveys and their potential for multisurvey analysis, this represents an important milestone in the path to enable population studies of photometric transients.

Water vapour retrieval using the Precision Solar Spectroradiometer

Abstract. The Precision Solar Spectroradiometer (PSR) is a new spectroradiometer developed at Physikalisch-Meteorologisches Observatorium Davos – World Radiation Center (PMOD–WRC), Davos, measuring direct solar irradiance at the surface, in the 300–1020 nm spectral range and at high temporal resolution. The purpose of this work is to investigate the instrument's potential to retrieve integrated water vapour (IWV) using its spectral measurements. Two different approaches were developed in order to retrieve IWV: the first one uses single-channel and wavelength measurements, following a theoretical water vapour high absorption wavelength, and the second one uses direct sun irradiance integrated at a certain spectral region. IWV results have been validated using a 2-year data set, consisting of an AERONET sun-photometer Cimel CE318, a Global Positioning System (GPS), a microwave radiometer profiler (MWP) and radiosonde retrievals recorded at Meteorological Observatorium Lindenberg, Germany. For the monochromatic approach, better agreement with retrievals from other methods and instruments was achieved using the 946 nm channel, while for the spectral approach the 934–948 nm window was used. Compared to other instruments' retrievals, the monochromatic approach leads to mean relative differences up to 3.3 % with the coefficient of determination (R2) being in the region of 0.87–0.95, while for the spectral approach mean relative differences up to 0.7 % were recorded with R2 in the region of 0.96–0.98. Uncertainties related to IWV retrieval methods were investigated and found to be less than 0.28 cm for both methods. Absolute IWV deviations of differences between PSR and other instruments were determined the range of 0.08–0.30 cm and only in extreme cases would reach up to 15 %.

Quantitative Neutron Dark-field Imaging through Spin-Echo Interferometry

Neutron dark-field imaging constitutes a seminal progress in the field of neutron imaging as it combines real space resolution capability with information provided by one of the most significant neutron scattering techniques, namely small angle scattering. The success of structural characterizations bridging the gap between macroscopic and microscopic features has been enabled by the introduction of grating interferometers so far. The induced interference pattern, a spatial beam modulation, allows for mapping of small-angle scattering signals and hence addressing microstructures beyond direct spatial resolution of the imaging system with high efficiency. However, to date the quantification in the small angle scattering regime is severely limited by the monochromatic approach. To overcome such drawback we here introduce an alternative and more flexible method of interferometric beam modulation utilizing a spin-echo technique. This novel method facilitates straightforward quantitative dark-field neutron imaging, i.e. the required quantitative microstructural characterization combined with real space image resolution. For the first time quantitative microstructural reciprocal space information from small angle neutron scattering becomes available together with macroscopic image information creating the potential to quantify several orders of magnitude in structure sizes simultaneously.

Relevance of Epistemological Pluralism for Resource Management Policies

The common believe of a single successful form of knowing the reality is misleading. A brief analysis of many human activities reveals a pluralistic perspective of several coexisting conceptual schemes that underlie the form in which women and men know and constitute the world in which we live. Here, I will discuss the necessity of taking seriously this pluralistic perspective when developing conceptual frameworks of human activities. As an example of great interest and importance, I will consider the case of resource management that has to contemplate the conservation and the response of ecosystems to human activities that may lead to irreversible damage. Ecosystems’ activity occurs over a wide range of space and time scales and, hence, policies and proposals of solutions to ecological problems should avoid narrow and monochromatic approaches. Specifically, the Pemon perspective of fire is a good example to show that for more robust and flexible resource management we need the knowledge and experience of different cultural and disciplinary groups.

A polychromatic approach to far-field superlensing at visible wavelengths

Breaking the diffraction barrier in the visible part of the electromagnetic spectrum is of fundamental importance. Far-field subwavelength focusing of light could, for instance, drastically broaden the possibilities available in nanolithography, light-matter interactions and sensing at the nanoscale. Similarly, imaging with a nanometric resolution could result in incredible breakthroughs in soft matter and biology. There have been numerous proposals in this regard based on metamaterials, structured illumination methods or diffractive optical components. The common denominator of all these approaches resides in their monochromatic nature. Here we show that using polychromatic light in dispersive metamaterials allows us to circumvent many limitations associated with previous monochromatic approaches. We design a plasmonic metalens based on metallic nanorods that, when used with broadband light fields, can beat the diffraction limit for imaging and focusing from the far field.

Subjective visual acuity with simulated defocus

Artificial degradation of vision by inducing dioptric blur is frequently used for evaluating diagnostic equipment. However, the use of lenses is prone to errors as it is adversely affected by eyelid squinting, pupil size, and imprecise lens position. The alternative is a degradation of the stimuli themselves based on a Fourier-optical mathematical model. With this, however, perceptual effects such as 'simultaneous blur' induced by the surround may affect acuity. We tested whether both methods, lens induced defocus and mathematical stimulus degradation, yield concordant results. We compared both methods in normal subjects, measuring Landolt C acuity at five different levels of defocus from 0 to 8 dioptres. The pupil size was determined individually, chromatic aberrations were avoided by using a monochromatic approach, and a correction for spectacle magnification was included. Otherwise, the experimental design was kept deliberately simple to remain comparable to typical applications. With the major sources of error associated with the use of lenses being accounted for, both methods yield similar mean results with differences in acuity ranging from <0.001 to 0.054 logMAR (0.2-13%). Using mathematically simulated defocus is a viable option if both reasonable accuracy and ease of use are required. The fact that the application of the mathematical model only blurs the stimulus itself, but not the surrounding environment, does not appear to be detrimental to the method.

Modeling wind waves and tidal flows in shallow micro-tidal basins

Observational evidence and mathematical modeling have demonstrated the crucial role of wind waves on sediment resuspension in shallow micro-tidal basins, where tidal fluxes alone are unable to mobilize tidal flat sediments. Carniello et al. (2005) presented a numerical model which combines wind waves with tidal fluxes in a shallow micro-tidal basin. The highly irregular bathymetry typical of these environments characterized by the presence of deep channels, emergent salt marshes and extensive tidal flats suggested the introduction of specific hypotheses while solving the wave action conservation equation to describe wind-wave generation and propagation. In particular, as suggested by field measurements, the wave spectrum in this type of environment is quite often very narrow. Thus Carniello et al. (2005) originally followed a monochromatic approach, further assuming that the direction of wave propagation instantaneously adjusts to the wind direction and a constant wave period both in space and time. In the present contribution, we relax the latter assumption by introducing a variable wave period through a suitable empirical power law which relates wave period to wind speed and flow depth, based on wind-wave data collected in the Venice Lagoon. The same relationship came out to fit quite well also data collected in Lake George (AU) and, more recently, data collected in a system of lagoons at the Virginia Coast Reserve, USA ( Mariotti et al., 2010). The noteworthy improvement in the estimation of wave height obtained by considering the local wave period is shown on the basis of the results of a number of simulations carried out for different storm events. The improvement obtained in the wind-wave field description reflects also on the estimation of the bottom shear stress and, therefore, on the description of the processes responsible for the morphological evolution of shallow tidal environments.

First City: Philadelphia and the Forging of Historical Memory (review)

Book Reviews61 Style. Several ofNew England's Chapel Style FMHs have cornerpilasters attached to a frieze, providing a regional distinctive touch. Gothic versions of the type date to the 1895-1910 era, and a single example of the Akron Plan was constructed at Oak Grove, Maine. Twentieth century FMHs (1920-2000) display little architectural cohesion. Since the book's publication, people have forwarded additional information to Silas, fueling the possibility of a second edition. Silas has also been in contact with other historians ofQuaker architecture. As a result, an expanded version would undoubtedly use the emerging typology rather than using terms from residential architecture (Georgian, Cape). Whether or not a new version materializes, New England Quaker Meetinghouses is an excellent resource for Friends historians, genealogists, architectural historians, and libraries. Seth B. HinshawDowningtown, Pa. First City: Philadelphia and the Forging ofHistorical Memory. By Gary B. Nash. Philadelphia: University of Pennsylvania Press, 2001. 383 pp. Illustrations, notes, index. Cloth $34.95. When Independence National Historical Park recently revealed its plans to build a new home for the Liberty Bell on the site of the slave quarters built by George Washington, Gary Nash led the charge of historians and community leaders who forced the Park Service to review and rework the interpretation of the site in order to recognize and remember Washington's slaves. Anything less, according to Nash, would be "murdering historical memory." Nash lives on the "cutting edge" of the field. He was among the first historians to challenge the old guard and their monochromatic approach to history, with its emphasis on great white Protestant males, by emphasizing the contributions oflittle-known people: African Americans, Native Americans , women, and other minority groups. His grass-roots approach, which once made him an outsider among the ivory tower establishment, has, today, made his work popular with those museum educators, public historians, and scholars who want to redefine the field in ways that go far beyond the dry, vocabulary-controlled interpretations of academics to a more engaging and inclusive approach. First City: Philadelphia and the Forging ofHistorical Memory is Nash's most recent gift to public history. Nash makes a compelling argument that Philadelphians, beginning in 62Quaker History the late eighteenth century, actively "participated in transmitting historical memory from one generation to another." Some were members of elite cultural institutions, such as historical societies and museums. Others belonged to relatively anonymous groups, such as women, blacks, and laborers. Regardless of their social and/or economic background, they engaged in memory-making in ways that "carried our their own ideological , cultural, and politically-informed agendas." (Page 8). Nash proves his case by exploring key eras in Philadelphia's eighteenth - and nineteenth-century past—early colonization, the American Revolution, early Republic, antebellum reform, Civil War, and Reconstruction —synthesizing a broad body ofsecondary literature, including his own scholarship. Just as insightful is Nash's familiarity with and interpretation of the artifact and manuscript collections of such institutions as the Library Company of Philadelphia, the American Philosophical Society, the Pennsylvania Academy ofthe Fine Arts, and the Historical Society of Pennsylvania. Perhaps the finest illustration ofdifferences in the construction ofPhiladelphia 's historical memory are the contrasting approaches of John Fanning Watson and George Lippard. Watson, the patrician founder of the Historical Society of Pennsylvania, sought to glorify the most prominent figures of the past by collecting their personal belongings, paintings, and manuscripts. For Watson, William Penn's Bible, a gateleg table from his country estate at Pennsbury, and the wampum belt presented to the Pennsylvania proprietor by a Lenape chief at the Shackamaxon treaty gathering , became engaging portholes to view Penn's almost mythological attempt to create a utopia in the wilderness for the persecuted peoples of Europe. But Watson's approach delivered the message that "great men make history and ordinary people follow their lead." (Page 18). On the other hand, Lippard, founder of the socialist Brotherhood ofthe Union, gave such "polite history" a bad name by celebrating the radical antecendents of Industrial Philadelphia and the common man's contributions to shaping the past. (Page 216). In Washington andHis Generals; or Legends ofthe American Revolution (1847), Lippard presented the War of Independence as a poor man's war...

Comparison of pitch angle diffusion by turbulent and monochromatic whistler waves

A recent Hamiltonian analysis of magnetized test particles acted on by a small monochromatic wave is compared to a quasi‐linear formulation of pitch angle diffusion by a turbulent spectrum of whistler waves. The quasi‐linear expression has previously been applied to anthropogenic VLF transmissions to conclude that they dominate pitch angle diffusion of inner radiation belt electrons. However, because these transmissions are very narrow in frequency range, the monochromatic approach might be more appropriate. It is shown analytically that the monochromatic limit of the quasi‐linear pitch angle diffusion coefficient reduces to the same expression as the diffusive regime of the Hamiltonian treatment. Agreement of the Hamiltonian pitch angle diffusion coefficient with the quasi‐linear values is verified numerically using realistic parameters for the spread in frequency and wave‐normal angle. As an aside, a simple, alternate derivation of quasi‐linear diffusion coefficients is given.

A Physical Formulation of Atmospheric Transmittances for the Massive Assimilation of Satellite Infrared Radiances

Abstract A continuous assimilation of high-density global satellite observations is required in order to improve numerical weather prediction analyses used to start forecasts. Until now, it was assumed that efficiency requirements imposed the use of regression-based models of atmospheric transmittance (typically on fixed pressure layers with coefficients varying for each layer) and prohibited the use of physically based models. Here, it is demonstrated that an explicit calculation of infrared transmittances for each absorbing gas (H2O, CO2, O3, CH4, N2O, and O2) can be done efficiently, provided that a monochromatic approach is followed as in a regression model such as Radiative Transfer for TOVS (the TIROS Operational Vertical Sounder) (operational in most weather centers). The classical Goody random model is chosen as a physical formulation for spectral line absorption along with established water vapor and oxygen continua parameterizations. Line-by-line transmittance calculations for 189 atmospheric pr...

Determination of the atmospheric-water-vapor content in the 940-nm absorption band by use of moderate spectral-resolution measurements of direct solar irradiance

We have analyzed three methods that can be used to determine the integrated water vapor of the atmosphere in the 940-nm band by means of modeled and measured direct solar spectral irradiance. The experimental irradiance data were obtained with a commercial LI-COR 1800 spectroradiometer, based on a monochromator system, of high to moderate spectral resolution (6 nm) in the 300-1100-nm range. The modeled data are based on monochromatic approaches to determine atmospheric transmittance constituents; for those of water vapor we used the lowtran7 model. The first method is a curve-fitting procedure that makes use of the entire shape band absorption information to retrieve a unique water-vapor value. The second method makes use of the monochromatic approach of the absorption transmittance formula to determine the amount of water vapor at each wavelength of the absorption band, and the third method is the classic differential absorption technique suitably applied to our data. Spectral analysis showed the advantages and disadvantages of each method, such as problems linked to the various spectral resolutions of the experimental and the modeled data, the width of the spectral range used to define the water-vapor absorption band, and the dependence of the retrieval on the choice of the two selected wavelengths in the last-named technique. All these problems were considered so they could be avoided or minimized and the associated errors estimated. We used the methods to determine water-vapor values for the period from March to November 1995 at a rural station in Vallodolid, Spain, allowing for the evaluation of the differences in real monitoring conditions. Finally, the contribution of continuum absorption was also evaluated, yielding lower water-vapor values between 13 and 30%. These differences were considerably greater than those that were due to the problems that we have just enumerated.

Radiative entropy production

THE radiative tensor obtained from the specular moments of the transfer equation is considered. The radiative entropy production is expressed in terms of this tensor. Contents The theory of gas radiation dates back to studies Rayleigh made over a century ago on the illumination and polarization of the sunlit sky. Since then, the theory has rapidly grown because of the efforts of astrophysicis ts and later of applied scientists and engineers. However, the entropy production associated with radiation apparently remains untreated and is the motivation of this study. As is well known, the entropy production results from dissipative processes (involving mass, species, momentum, and/or heat transfer and electromagnetic or nuclear transport). Less known is the fact that the dissipation may have a diffusive or hysteretic origin, the diffusion being directional and the hysteresis being cyclic. However, except for a few cases (such as strain hardening and the magnetic saturation), the majority of dissipative processes (including the dissipation of radiation) are of diffusive nature. A recent study by Arpaci 1 shows, in terms of the radiative stress obtained from the specular (kinetic) moments of the transfer equation, the diffusive nature of radiation for any optical thickness. Accordingly, the expression to be developed for entropy production is in terms of this stress and includes also the dissipation resulting from the conduction of heat and viscous friction. First, some remarks on the radiative stress are needed. These will be made in terms of spectrally averaged radiation because of its simplicity. A monochromatic approach, which may be needed for a quantitative study, is not essential here because of the conceptual nature of the intended study. As pointed out by Felske and Tien,2 there are a variety of practical situations in which scattering is not important. For these situations, consider the spectrally averaged transfer equation,