The Experts below are selected from a list of 78 Experts worldwide ranked by ideXlab platform
Alexander Marshak - One of the best experts on this subject based on the ideXlab platform.
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the Spectral Invariant approximation within canopy radiative transfer to support the use of the epic dscovr oxygen b band for monitoring vegetation
Journal of Quantitative Spectroscopy & Radiative Transfer, 2017Co-Authors: Alexander Marshak, Yuri KnyazikhinAbstract:EPIC (Earth Polychromatic Imaging Camera) is a 10-channel spectroradiometer onboard DSCOVR (Deep Space Climate Observatory) spacecraft. In addition to the near-infrared (NIR, 780 nm) and the 'red' (680 nm) channels, EPIC also has the O2 A-band (764±0.2 nm) and B-band (687.75±0.2 nm). The EPIC Normalized Difference Vegetation Index (NDVI) is defined as the difference between NIR and 'red' channels normalized to their sum. However, the use of the O2 B-band instead of the 'red' channel mitigates the effect of atmosphere on remote sensing of surface reflectance because O2 reduces contribution from the radiation scattered by the atmosphere. Applying the radiative transfer theory and the Spectral Invariant approximation to EPIC observations, the paper provides supportive arguments for using the O2 band instead of the red channel for monitoring vegetation dynamics. Our results suggest that the use of the O2 B-band enhances the sensitivity of the top-of-atmosphere NDVI to the presence of vegetation.
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Observed Spectral Invariant behavior of zenith radiance in the transition zone between cloud-free and cloudy regions
2010 2nd Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing, 2010Co-Authors: Alexander Marshak, Yuri Knyazikhin, C. Chiu, Warren J WiscombeAbstract:The Atmospheric Radiation Measurement Program's (ARM) new Shortwave Spectrometer (SWS) looks straight up and measures zenith radiance at 418 wavelengths between 350 and 2200 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A surprising Spectral Invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free atmosphere. This behavior suggests that the Spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is found to be a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. This new finding may help us to better understand and quantify such physical phenomena as humidification of aerosols in the relatively moist cloud environment and evaporation and activation of cloud droplets.
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Spectral Invariant behavior of zenith radiance around cloud edges observed by arm sws
Geophysical Research Letters, 2009Co-Authors: Alexander Marshak, Yuri Knyazikhin, J C Chiu, Warren J WiscombeAbstract:The ARM Shortwave Spectrometer (SWS) measures zenith radiance at 418 wavelengths between 350 and 2170 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A Spectral Invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free. This behavior suggests that the Spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. An important result of these discoveries is that high temporal resolution radiance measurements in the clear-to-cloud transition zone can be well approximated by lower temporal resolution measurements plus linear interpolation.
Warren J Wiscombe - One of the best experts on this subject based on the ideXlab platform.
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Observed Spectral Invariant behavior of zenith radiance in the transition zone between cloud-free and cloudy regions
2010 2nd Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing, 2010Co-Authors: Alexander Marshak, Yuri Knyazikhin, C. Chiu, Warren J WiscombeAbstract:The Atmospheric Radiation Measurement Program's (ARM) new Shortwave Spectrometer (SWS) looks straight up and measures zenith radiance at 418 wavelengths between 350 and 2200 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A surprising Spectral Invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free atmosphere. This behavior suggests that the Spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is found to be a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. This new finding may help us to better understand and quantify such physical phenomena as humidification of aerosols in the relatively moist cloud environment and evaporation and activation of cloud droplets.
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Spectral Invariant behavior of zenith radiance around cloud edges observed by arm sws
Geophysical Research Letters, 2009Co-Authors: Alexander Marshak, Yuri Knyazikhin, J C Chiu, Warren J WiscombeAbstract:The ARM Shortwave Spectrometer (SWS) measures zenith radiance at 418 wavelengths between 350 and 2170 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A Spectral Invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free. This behavior suggests that the Spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. An important result of these discoveries is that high temporal resolution radiance measurements in the clear-to-cloud transition zone can be well approximated by lower temporal resolution measurements plus linear interpolation.
Yuri Knyazikhin - One of the best experts on this subject based on the ideXlab platform.
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the Spectral Invariant approximation within canopy radiative transfer to support the use of the epic dscovr oxygen b band for monitoring vegetation
Journal of Quantitative Spectroscopy & Radiative Transfer, 2017Co-Authors: Alexander Marshak, Yuri KnyazikhinAbstract:EPIC (Earth Polychromatic Imaging Camera) is a 10-channel spectroradiometer onboard DSCOVR (Deep Space Climate Observatory) spacecraft. In addition to the near-infrared (NIR, 780 nm) and the 'red' (680 nm) channels, EPIC also has the O2 A-band (764±0.2 nm) and B-band (687.75±0.2 nm). The EPIC Normalized Difference Vegetation Index (NDVI) is defined as the difference between NIR and 'red' channels normalized to their sum. However, the use of the O2 B-band instead of the 'red' channel mitigates the effect of atmosphere on remote sensing of surface reflectance because O2 reduces contribution from the radiation scattered by the atmosphere. Applying the radiative transfer theory and the Spectral Invariant approximation to EPIC observations, the paper provides supportive arguments for using the O2 band instead of the red channel for monitoring vegetation dynamics. Our results suggest that the use of the O2 B-band enhances the sensitivity of the top-of-atmosphere NDVI to the presence of vegetation.
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Observed Spectral Invariant behavior of zenith radiance in the transition zone between cloud-free and cloudy regions
2010 2nd Workshop on Hyperspectral Image and Signal Processing: Evolution in Remote Sensing, 2010Co-Authors: Alexander Marshak, Yuri Knyazikhin, C. Chiu, Warren J WiscombeAbstract:The Atmospheric Radiation Measurement Program's (ARM) new Shortwave Spectrometer (SWS) looks straight up and measures zenith radiance at 418 wavelengths between 350 and 2200 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A surprising Spectral Invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free atmosphere. This behavior suggests that the Spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is found to be a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. This new finding may help us to better understand and quantify such physical phenomena as humidification of aerosols in the relatively moist cloud environment and evaporation and activation of cloud droplets.
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Spectral Invariant behavior of zenith radiance around cloud edges observed by arm sws
Geophysical Research Letters, 2009Co-Authors: Alexander Marshak, Yuri Knyazikhin, J C Chiu, Warren J WiscombeAbstract:The ARM Shortwave Spectrometer (SWS) measures zenith radiance at 418 wavelengths between 350 and 2170 nm. Because of its 1-sec sampling resolution, the SWS provides a unique capability to study the transition zone between cloudy and clear sky areas. A Spectral Invariant behavior is found between ratios of zenith radiance spectra during the transition from cloudy to cloud-free. This behavior suggests that the Spectral signature of the transition zone is a linear mixture between the two extremes (definitely cloudy and definitely clear). The weighting function of the linear mixture is a wavelength-independent characteristic of the transition zone. It is shown that the transition zone spectrum is fully determined by this function and zenith radiance spectra of clear and cloudy regions. An important result of these discoveries is that high temporal resolution radiance measurements in the clear-to-cloud transition zone can be well approximated by lower temporal resolution measurements plus linear interpolation.
Radomir S Stankovic - One of the best experts on this subject based on the ideXlab platform.
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Spectral Invariant operations in the p valued Spectral domain
International Symposium on Multiple-Valued Logic, 2019Co-Authors: Claudio Moraga, Milena Stankovic, Radomir S StankovicAbstract:The paper studies the generation of ternary bent functions by permuting the circular Vilenkin-Chrestenson spectrum of a known bent function. We call this Spectral Invariant operations in the Spectral domain, in analogy to the Spectral Invariant operations in the domain of the functions. Furthermore, related generalized permutations are derived to obtain new bent functions in the original domain.
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an improved Spectral classification of boolean functions based on an extended set of Invariant operations
Facta universitatis. Series electronics and energetics, 2018Co-Authors: Milena Stankovic, Claudio Moraga, Radomir S StankovicAbstract:Boolean functions expressing some particular properties often appear in engineering practice. Therefore, a lot of research efforts are put into exploring different approaches towards classification of Boolean functions with respect to various criteria that are typically selected to serve some specific needs of the intended applications. A classification is considered to be strong if there is a reasonably small number of different classes for a given number of variables n and it it desir able that classificationrules are simple. A classification with respect to Walsh Spectral coefficients, introduced formerly for digital system design purposes, appears to be useful in the context of Boolean functions used in cryptography, since it is ina way compatible with characterization of cryptographically interesting functions through Walsh Spectral coefficients. This classification is performed in terms of certain Spectral Invariant operations. We show by introducing a new Spectral Invariant operation in the Walsh domain, that by starting from n≤5, some classes of Boolean functions can be merged which makes the classification stronger, and from the theoretical point of view resolves a problem raised already in seventies of the last century. Further, this new Spectral Invariant operation can be used in constructing bent functions from bent functions represented by quadratic forms.
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some Spectral Invariant operations for multiple valued functions with homogeneous disjoint products in the polynomial form
International Symposium on Multiple-Valued Logic, 2017Co-Authors: Milena Stankovic, Claudio Moraga, Radomir S StankovicAbstract:It has long been known that some transformationsof the Boolean functions affect only the permutation of somesubset of coefficients in the Walsh-Hadamard spectrum or justchange the sign of some coefficients. These operations are knownas Spectral Invariant operations. It exists a generalization of theseInvariant operations for multi-valued functions and Vilenkin-Chrestenson spectrum. Here some new Spectral Invariant operationswill be defined for functions with p = 3 and with n 5 variables, which have disjoint products of two variables in theirpolynomial forms. As a result of these new operations only thevalues of some subsets of Spectral coefficients will by permuted, like in the case of Invariant operations which are known untilnow. This property of Spectral Invariant operations has importantconsequences on multiple-valued bent functions. Any functionobtained by the application of one or more Spectral Invariantoperations to a bent function will be also a bent function. It willbe shown that the defined new Invariant operations are usefulfor characterization of multi-valued bent functions.
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some Spectral Invariant operations for functions with disjoint products in the polynomial form
Computer Aided Systems Theory, 2017Co-Authors: Milena Stankovic, Claudio Moraga, Radomir S StankovicAbstract:It has long been known that some transformations of a binary function produce a permutation of some coefficients in the Walsh-Hadamard spectrum or just change the sign of some coefficients. Those operations are known as Spectral Invariant operations. In this paper some new Spectral Invariant operations are defined for the functions representable by disjoint quadratic polynomial forms. It is shown that these new Invariant operations are useful for characterization of the bent functions.
Shuyun Wei - One of the best experts on this subject based on the ideXlab platform.
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Spectral Invariant subalgebras of reduced crossed product c algebras
Journal of Functional Analysis, 2003Co-Authors: Xiaoman Chen, Shuyun WeiAbstract:Abstract Let G be a discrete group with a proper length function l. In this paper, we prove that the Schwartz space S2l(G,A) is a Spectral Invariant dense subalgebra of the reduced crossed product C r ∗ (G,A) for all commutative C ∗ -algebra A with a G-action if and only if G has polynomial growth with respect to l.