Spectral Nature Research Articles

The Spectral Response of the Landsat-8 Operational Land Imager

Abstract: This paper discusses the pre-launch spectral characterization of the Operational Land Imager (OLI) at the component, assembly and instrument levels and relates results of those measurements to artifacts observed in the on-orbit imagery. It concludes that the types of artifacts observed and their magnitudes are consistent with the results of the pre-launch characterizations. The OLI in-band response was characterized both at the integrated instrument level for a sampling of detectors and by an analytical stack-up of component measurements. The out-of-band response was characterized using a combination of Focal Plane Module (FPM) level measurements and optical component level measurements due to better sensitivity. One of the challenges of a pushbroom design is to match the spectral responses for all detectors so that images can be flat-fielded regardless of the spectral nature of the targets in the imagery. Spectral variability can induce striping (detector-to-detector variation), banding (FPM-to-FPM variation) and other artifacts in the final data products. Analyses of the measured spectral response showed that the maximum discontinuity between FPMs due to spectral filter differences is 0.35% for selected targets for all bands except for Cirrus, where there is almost no signal. The average discontinuity between FPMs is 0.12% for the same targets. These results were expected and are in accordance with the OLI requirements. Pre-launch testing identified low levels (within requirements) of spectral crosstalk amongst the three HgCdTe (Cirrus, SWIR1 and SWIR2) bands of the OLI and on-orbit data confirms this crosstalk in the imagery. Further post-launch analyses and simulations revealed that the strongest crosstalk effect is from the SWIR1 band to the Cirrus band; about 0.2% of SWIR1 signal leaks into the Cirrus. Though the total crosstalk signal is only a few counts, it is evident in some scenes when the in-band cirrus signal is very weak. In moist cirrus-free atmospheres and over typical land surfaces, at least 30% of the cirrus signal was due to the SWIR1 band. In the SWIR1 and SWIR2 bands, crosstalk accounts for no more than 0.15% of the total signal.

Spectral Emissivity of Roof Membranes and Vapor Barriers

Optical parameters become to the features that are currently taken into account more frequently. There are various reasons of dealing with those parameters. Some of them are due to thermal calculation purposes while the other one are trying to consider low-emissivity functions of various innovative building materials. The paper is focused on spectral emissivity analysis of roof membranes and vapor barriers especially that are applied in sloped roofs and walls with air ventilated cavity. The spectral emissivity in the longwave radiation region was assessed by laboratory method of an infrared spectroscopy. The results present courses of spectral nature as well as its transformation into weighted values. As a result the final comparison demonstrates facts of aiming to point out the possibility of receiving any benefit for thermal aspects purpose.

A study on aerodynamic sound from an externally excited flexible structure in flow

Aerodynamic far field sound generated from an elastic structure vibrating in flow under the influence of external excitation is investigated. A test assembly of a rigid square bluff body with an elastic trailing plate in a steady flow at low Reynolds number and low Mach number is considered. Along with the explicit external harmonic force excitation, the trailing plate experiences excitation from the flow vortices generated from the frontal bluff body. A two-way fluid–structure interaction model is implemented, ensuring a bi-directional coupling between the flow field and vibrating structure. For computing acoustic propagation field, a linearized Euler equation based surface coupling type computational aeroacoustic (CAA) hybrid method is used. A surface source coupling is considered between the flow and acoustic domain and the source term is calculated by unsteady compressible flow computation. The focus of the study is to investigate the effects of additional external forced excitation on the aerodynamic sound generated from a flow-induced vibration of the elastic structure. Several test cases at different external excitation (amplitudes and frequencies) forces are solved and the resultant aerodynamic sound is compared with the case of aerodynamic sound from the structure vibrating in flow in absence of such external excitations. The character of the resultant far field aerodynamic sound is significantly influenced by the harmonic force excitation of the elastic plate. For a certain range of force amplitude, a noticeable effect of reduction in far field acoustic pressure is observed. Dependence of the spectral nature of the acoustic pressure on the parameters of excitation (amplitude and frequency) is discussed. It is also observed that the directivity lobes of far field sound pressure are stretched in the downstream direction in the case of external excitation and their inclination increases with the force amplitude.

Intermediate Mass Black Holes: Their Motion and Associated Energetics

There is a lot of current astrophysical evidence and interest in intermediate mass black holes (IMBH), ranging from a few hundred to several thousand solar masses. The active galaxy M82 and the globular cluster G1 in M31, for example, are known to host such objects. Here, we discuss several aspects of IMBH such as their expected luminosity, spectral nature of radiation, and associated jets. We also discuss possible scenarios for their formation including the effects of dynamical friction, and gravitational radiation. We also consider their formation in the early universe and also discuss the possibility of supermassive black holes forming from mergers of several IMBH and compare the relevant time scales involved with other scenarios.

Changing diagnostic practices: autism spectrum disorder

SummaryIn medical practice it is crucial that symptom descriptions are as precise and objective as possible, which psychiatry attempts to achieve through its psychopathological lexicon. The term ‘autism spectrum disorder’ has now entered psychiatric nosology, but the symptom definitions on which it is based are not robust, potentially making reliable and valid diagnoses a problem. This is further compounded by the spectral nature of the disorder and its lack of clear diagnostic boundaries. To overcome this, there is a need for a psychopathological lexicon of 'social cognition’ and a classification system that splits rather than lumps disorders with core difficulties in social interaction.

DETAILED INVESTIGATIONS OF THE DIMMEST BURSTS FROM TWO MAGNETARS, SGR J0501+4516 AND SGR J1550–5418

We applied the Bayesian blocks representation technique to search for the dimmest bursts from two magnetars: we identified 320 events from SGR J0501+4516 using a deep XMM-Newton observation and 404 bursts from SGR J1550-5418 using two Swift/XRT pointings. The fluence level of our sample for both sources are about 1-2 orders of magnitude lower than earlier studies. We systematically investigated morphological characteristics and duration distributions of these bursts, as these properties are directly obtained from their Bayesian blocks profiles. We also studied the spectral behavior of the dimmest bursts, which were grouped based on the morphological types and fluences. Our results helped us further differentiate the spectral nature of very dim bursts from that of the persistent emission, both fitted with physically motivated continuum emission models. Moreover, we generated the differential burst fluence distribution for these two magnetars in the lowest fluence regime.

Ghost writing: photographing (the) spectral north

This paper explores photography’s spectral nature in relation to the concept of difference, as theorised by Jacques Derrida. What emerges is a way of thinking about photography as a kind of ghost writing. Derrida’s assertion of the importance of photography’s idiomatic logic is actively applied here to perceptions and representations of north. We are alerted to the instability of north by the various definitions currently in use by the Ordnance Survey in Great Britain. This allows us to think about north in terms of the disruption of self-identity found at the core of Derrida’s thinking about photography and to understand differential north via photography’s spectral logic, which ‘traces a relation of haunting’ between the opposition north/south. In addition, Magnetic North is unlocatable in any permanent sense given that it is constantly moving and problematised by our mistaken conventions of naming. The spectral north emerges as a productive term which resonates with specific landscapes on the periphery of Britain. In these landscapes, which contain the remains of wartime defences, the irruption of the past is keenly felt, producing unsettling experiences for the visitor. I present photographic fieldwork from these wartime coastal batteries and consider both the images and place in terms of Tim Edensor’s ‘mundane spaces’ where the trace of the spectre is free to roam. These inscribed landscapes, archives in a sense, are complex imbrications of different timeframes and historic resonances. They provide a particularly fertile location for a medium such as photography, given its peculiar relationship with time.

The Spectral Nature of Maximum Likelihood Noise Compensated Linear Prediction

The effects of noise in autoregressive (AR) analysis (or linear prediction) and its compensation (NCAR) has been commonly carried out in the time domain under the least square (LS) criterion. This paper studies the adequacy of such an approach by means of a comparative analysis with selected frequency-based NCAR methods. In particular, the maximization of the spectral likelihood (ML) results in a proper optimization problem that is easy to solve and brings useful insights into the rationale of the NCAR problem. On the contrary, popular time-based NCAR methods are shown in the paper to be designed, in the ML context, around ill-conditioned criteria, requiring constraints to guarantee stable solutions. The statistical analysis on a realistic scenario as well as an experiment on speech enhancement complement this analysis.

9. Network density and synaptic weight mechanisms for non-evoked transitions in cognition and EEG

A major challenge in neuroscience is to understand how neural systems respond to external stimuli. An often ignored but even greater challenge is to understand how neural systems make decisions independently of external input. In this presentation we will show how two complementary mechanisms can support and modulate autonomous transitions in complex persistent activity: (1) network density and (2) synaptic weights. Computational models with random, ring and spatial connectivity are applied to help illustrate how changes in synaptic weights can effect changes to frequencies and the occurrence of frequency sweeps observed in EEG recordings. Simulations iterating across excitatory and inhibitory weight combinations (E → E; E → I; I → E; I → I) show that changes in all types of connections can have non-linear effects on activity propagation properties. For example, changing excitatory → excitatory connections in a network with fixed density can result in large shifts in activity frequency. Peak population frequencies range from approximately 20 Hz to 80 Hz with a tendency to rise as the E → E weighting is increased. These changes in spectral properties tend to be even more complex and non-monotonic in response to changes in connections to and from inhibitory populations. In turn, changes to the cellular density of two- and three-dimensional networks alter the spatial and spectral nature of activity propagation allowing for complex formations such as spiral waves and the emergence of autonomous transitions. Together, the co-modulation of weight and density parameters allows for complex, persistent activity with a range of frequency distributions and autonomous transitions patterns. The effects of the interactions of these two mechanisms suggest that alterations to network density along with weight modulations may be key factors in enabling EEG transitions that can occur independently of external input. The two mechanisms may thus be important evolutionary, developmental, and learning strategies for dynamical tuning of neural population activity underlying cognition. Support contributed by: CIHR, NIH.

Quantitative comparison of the variability in observed and simulated shortwave reflectance

Abstract. The Climate Absolute Radiance and Refractivity Observatory (CLARREO) is a climate observation system that has been designed to monitor the Earth's climate with unprecedented absolute radiometric accuracy and SI traceability. Climate Observation System Simulation Experiments (OSSEs) have been generated to simulate CLARREO hyperspectral shortwave imager measurements to help define the measurement characteristics needed for CLARREO to achieve its objectives. To evaluate how well the OSSE-simulated reflectance spectra reproduce the Earth's climate variability at the beginning of the 21st century, we compared the variability of the OSSE reflectance spectra to that of the reflectance spectra measured by the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY). Principal component analysis (PCA) is a multivariate decomposition technique used to represent and study the variability of hyperspectral radiation measurements. Using PCA, between 99.7% and 99.9% of the total variance the OSSE and SCIAMACHY data sets can be explained by subspaces defined by six principal components (PCs). To quantify how much information is shared between the simulated and observed data sets, we spectrally decomposed the intersection of the two data set subspaces. The results from four cases in 2004 showed that the two data sets share eight (January and October) and seven (April and July) dimensions, which correspond to about 99.9% of the total SCIAMACHY variance for each month. The spectral nature of these shared spaces, understood by examining the transformed eigenvectors calculated from the subspace intersections, exhibit similar physical characteristics to the original PCs calculated from each data set, such as water vapor absorption, vegetation reflectance, and cloud reflectance.

NUCLEAR RADIO JET FROM A LOW-LUMINOSITY ACTIVE GALACTIC NUCLEUS IN NGC 4258

The nearby low-luminosity active galactic nucleus (LLAGN) NGC 4258 has a weak radio continuum component at the galactic center. We investigate its radio spectral properties on the basis of our new observations using the Nobeyama Millimeter Array at 100 GHz and archival data from the Very Large Array (VLA) at 1.7-43 GHz and the James Clerk Maxwell telescope at 347 GHz. The NGC 4258 nuclear component exhibits (1) an intra-month variable and complicated spectral feature at 5-22 GHz and (2) a slightly inverted spectrum at 5-100 GHz (a spectral index of ~0.3) in time-averaged flux densities, which are also apparent in the closest LLAGN M81. These similarities between NGC 4258 and M81 in radio spectral natures in addition to previously known core shift in their AU-scale jet structures produce evidence that the same mechanism drives their nuclei. We interpret the observed spectral property as the superposition of emission spectra originating at different locations with frequency-dependent opacity along the nuclear jet. Quantitative differences between NGC 4258 and M81 in terms of jet/counter jet ratio, radio loudness, and degree of core shift can be consistently understood by fairly relativistic speeds (bulk Lorentz factors of >~ 3) of jet and their quite different inclinations. The picture established from the two closest LLAGNs is useful for understanding the physical origin of unresolved and flat/inverted spectrum radio cores that are prevalently found in LLAGNs, including Sgr A*, with starved supermassive black holes in the present-day universe.

Spatial coherence measurement of polychromatic light with modified Young’s interferometer

Partial spatial coherence is a fundamental concept in optical systems. Theoretically, the normalized mutual coherence function gives a quantitative measure for partial spatial coherence regardless of the spectral nature of the radiation. For narrowband light the degree of spatial coherence can be measured in terms of the fringe modulation in the classic Young's two-pinhole interferometer. Though not commonly appreciated, with polychromatic radiation this is not the case owing to the wavelength dependence of diffraction. In this work we show that with a modified two-beam interferometer containing an achromatic Fresnel transformer the degree of spatial coherence is again related to the visibility of intensity fringes in Young's experiment for any polychromatic light. This result, which is demonstrated both theoretically and experimentally, thus restores the usefulness of the two-pinhole interferometer in the measurement of the spatial coherence of light beams of arbitrary spectral widths.

The Permanent Collection as Larval Specter: Recent Artist Interventions in the Museum Space

In his chapter On the Uses and Disadvantages of Living among Specters, from Nudities, Giorgio Agamben examines the state of outmoded spaces, which employ signs and signatures to tell somewhat indecipherable stories about their once-great pasts. Although Agamben focuses on cities, specifically Venice in his chapter, I will apply this concept to the museum as an institution and a house for a collection. The inanimate nature of a museum's gallery spaces and permanent collection combined with the compulsory complacency of its stewards tends to result in a house for dead art objects. This paper will examine two recent exhibitions designed by contemporary artists Jan Fabre and Robert Gober that intervened in the permanent collections of their respective institutions, thus revealing the collections' spectral natures. Using the framework of Giorgio Agamben's chapter, I will demonstrate the contemporary artist's use of pre-existing collections to alter viewer perception in a way that is relevant to the artist and denotes the passage of time through a markedly different frame of reference. Jan Fabre and Robert Gober employ aesthetic languages in their own work that interact harmoniously with the permanent collections in which they have held exhibitions. By juxtaposing their contemporary work against relics of the past, Fabre and Gober demonstrate how their aesthetic influences have changed over time.

Thermal conductivity of nano-grained SrTiO3 thin films

We measure the thermal conductivities of nano-grained strontium titanate (ng-SrTiO3) films deposited on sapphire substrates via time-domain thermoreflectance. The 170 nm thick oxide films of varying grain-size were prepared from a chemical solution deposition process. We find that the thermal conductivity of ng-SrTiO3 decreases with decreasing average grain size and attribute this to increased phonon scattering at grain boundaries. Our data are well described by a model that accounts for the spectral nature of anharmonic Umklapp scattering along with grain boundary scattering and scattering due to the film thickness.

Local spectral theory for normal operators in Krein spaces

AbstractSign type spectra are an important tool in the investigation of spectral properties of selfadjoint operators in Krein spaces. It is our aim to show that also sign type spectra for normal operators in Krein spaces provide insight in the spectral nature of the operator: If the real part and the imaginary part of a normal operator in a Krein space have real spectra only and if the growth of the resolvent of the imaginary part (close to the real axis) is of finite order, then the normal operator possesses a local spectral function defined for Borel subsets of the spectrum which belong to positive (negative) type spectrum. Moreover, the restriction of the normal operator to the spectral subspace corresponding to such a Borel subset is a normal operator in some Hilbert space. In particular, if the spectrum consists entirely out of positive and negative type spectrum, then the operator is similar to a normal operator in some Hilbert space. We use this result to show the existence of operator roots of a class of quadratic operator polynomials with normal coefficients.

Music and Hearing Aids—An Introduction

Modern digital hearing aids have provided improved fidelity over those of earlier decades for speech. The same however cannot be said for music. Most modern hearing aids have a limitation of their "front end," which comprises the analog-to-digital (A/D) converter. For a number of reasons, the spectral nature of music as an input to a hearing aid is beyond the optimal operating conditions of the "front end" components. Amplified music tends to be of rather poor fidelity. Once the music signal is distorted, no amount of software manipulation that occurs later in the circuitry can improve things. The solution is not a software issue. Some characteristics of music that make it difficult to be transduced without significant distortion include an increased sound level relative to that of speech, and the crest factor- the difference in dB between the instantaneous peak of a signal and its RMS value. Clinical strategies and technical innovations have helped to improve the fidelity of amplified music and these include a reduction of the level of the input that is presented to the A/D converter.

On the role of spectral markers and stability in spine models

We considered various stability issues related to biomechanical models of the spine, taking as our point of departure the scalar quantities proposed in Howarth et al. (2004). We discussed their significance and applicability by considering some mechanical toy models. In particular, we analysed the relevance of the behaviour of some of these measurements, namely, the determinant of the Hessian matrix and other quantities containing information of a similar spectral nature, and the role they may play in this type of studies. We showed that although in some cases these markers contain information about the load acting on the subject, this information may also be masked and not be detectable from these indexes.These models also allowed us to see how a system with these characteristics may become highly sensitive even to small load changes, and prompted us to put forward the hypothesis that trying to preserve stability at all costs might, under some circumstances, be an actual cause for system damage.

Electronic–nuclear entanglement in a conjugated polymer aggregate with a conical intersection: spectral signatures

We have studied the role of the electronic–nuclear entanglement in the emission properties of two interacting conjugated polymer chains forming an aggregate. The effect of disorder generally found in these systems is realized through a torsional degree of freedom which is responsible for a conical intersection of the adiabatic potential energy surfaces of the two excitonic states. The transition of the spectral nature of the aggregate from dimeric to monomeric form appears at the conical intersection point with vanishing entanglement of the emitting excitonic state. It is characterized by the nontrivial dependence of the emission rate for two perpendicular polarizations as a function of the torsion angle corresponding to different static disordered configurations. The exciton population dynamics shows direct connection to the entanglement evolution with the oscillations in population giving maximally entangled states as well as entanglement sudden death. A thorough analysis of the reduced densities of the nuclear degrees of freedom reveals that these extrema of entanglement can be connected to the passage of the system through the conical intersection for the range of interaction strength generally found in these systems.

High vertical resolution analyses of gravity waves and turbulence at a midlatitude station

We proposed a broad spectral data‐analyzing method to study the altitude and seasonal variability of gravity wave (GW)‐associated dynamics in the lower atmosphere at a midlatitude by using the radiosonde data from Miramar Nas (32.87°N, 117.15°W), California, during 1998–2008. Generally, the presented primary statistical features of GW parameters and their seasonal variation are consistent with previous radiosonde observations by using the conventional hodograph analysis method based on monochromatic GW theory. These consistencies suggest our proposed analyzing method is feasible in extracting GW parameters from the radiosonde data. More interesting, our analyses can reveal the altitude variations of GW parameters, which have been seldom reported in previous radiosonde observations. Similar to previous observations, most seasonal and height variability of GW parameters is closely connected with tropospheric jet, suggesting the important role of the jet in determining GW parameters as well as the lower atmospheric dynamics and thermal structure. Mainly due to the broad spectral nature of the observed GWs, there are also some differences between our results and previous studies based on monochromatic GW extraction. By using the perturbation of vertical ascent rate, we directly calculated GW momentum and heat fluxes, which can only be indirectly derived from the hodograph analysis. Furthermore, the directly derived heat flux can explain the frequently observed tropospheric inversion in winter. Besides GW parameters, turbulent energy dissipation rate and diffusion coefficient were also derived. The derived turbulence parameters and their altitude variations are in good agreement with radar observations reported elsewhere.

Spectral analysis of time changes of horocycle flows

We prove (under the condition of A. G. Kushnirenko) that all time changes of thehorocycle flow have purely absolutely continuous spectrum in the orthocomplement ofthe constant functions. This provides an answer to a question of A. Katok and J.-P.Thouvenot on the spectral nature of time changes of horocycle flows. Our proofs relyon positive commutator methods for self-adjoint operators.