Solar flux and its variations

Smith, Elske V. P.; Gottlieb, D. M.

doi:10.1007/bf00182600

Cited by 111 publications

(52 citation statements)

References 69 publications

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“…There is insufficient documentation on the Kurucz (1995) solar model and atomic and molecular data sources to compare with those used in our calculations. The Wehrli (1985) spectrum is positively biased relative to the Kondratyev et al (1965) and Murcray et al (1964) data points, despite the fact that these data were the ultimate source for the Smith and Gottlieb (1974) fits adopted by Wehrli; however, as noted in the section 2, the limb-darkening curve used by Smith and Gotlieb to convert these data to irradiance is not likely the same as the curve used by Pierce and Allen (1977), whose tabular values are shown in Fig. 1. …”

Section: B Model Spectrum and Comparisons With Other Datasetsmentioning

confidence: 96%

“…The World Radiation Center (WRC) Reference Spectrum (Wehrli 1985) adopted by the World Meteorological Organization (WMO) is a compilation from a number of sources. For the present discussion, irradiance in the midwave infrared portion of the spectrum comes from Smith and Gottlieb (1974), which is in turn, a compilation of several sources. All data points from Smith and Gottlieb in the 3.7-m spectral region are from the few Koutchmy and Peyturaux (1970) and Murcray et al (1964) radiance measurements previously discussed; again, no information is given regarding the limb-darkening curves used for the radiance to irradiance conversion in this spectral region.…”

Section: Overview Of Historical 37-m Spectral Irradiance Datasetsmentioning

confidence: 99%

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Model Calculations of Solar Spectral Irradiance in the 3.7-μm Band for Earth Remote Sensing Applications

Platnick

Fontenla

2008

Journal of Applied Meteorology and Climatology

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Since the launch of the first Advanced Very High Resolution Radiometer (AVHRR) instrument aboard the Television and Infrared Observational Satellite (TIROS-N), measurements in the 3.7-m atmospheric window have been exploited for use in cloud detection and screening, cloud thermodynamic phase and surface snow/ice discrimination, and quantitative cloud particle size retrievals. The utility of the band has led to the incorporation of similar channels on a number of existing satellite imagers and future operational imagers. Daytime observations in the band include both reflected solar and thermal emission energy. Since 3.7-m channels are calibrated to a radiance scale (via onboard blackbodies), knowledge of the top-ofatmosphere solar irradiance in the spectral region is required to infer reflectance. Despite the ubiquity of 3.7-m channels, absolute solar spectral irradiance data come from either a single measurement campaign (Thekaekara et al.) or synthetic spectra. In the current study, the historical 3.7-m band spectral irradiance datasets are compared with the recent semiempirical solar model of the quiet sun by Fontenla et al. The model has expected uncertainties of about 2% in the 3.7-m spectral region. The channel-averaged spectral irradiances using the observations reported by Thekaekara et al. are found to be 3.2%-4.1% greater than those derived from the Fontenla et al. model for Moderate Resolution Imaging Spectroradiometer (MO-DIS) and AVHRR instrument bandpasses; the Kurucz spectrum, as included in the Moderate Spectral Resolution Atmospheric Transmittance (MODTRAN4) distribution, gives channel-averaged irradiances 1.2%-1.5% smaller than the Fontenla model. For the MODIS instrument, these solar irradiance uncertainties result in cloud microphysical retrieval uncertainties that are comparable to other fundamental reflectance error sources.

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Section: B Model Spectrum and Comparisons With Other Datasetsmentioning

confidence: 96%

Section: Overview Of Historical 37-m Spectral Irradiance Datasetsmentioning

confidence: 99%

Model Calculations of Solar Spectral Irradiance in the 3.7-μm Band for Earth Remote Sensing Applications

Platnick

Fontenla

2008

Journal of Applied Meteorology and Climatology

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“…Aperture photometry is performed using 2 and 3 pixel radius apertures and aperture corrections published in the IRAC data handbook. We calculate color corrections assuming a solar spectral slope through the IRAC channels (Smith & Gottlieb 1974). Final fluxes are the average of all sixteen frames (omitting outliers), and the 1-sigma uncertainties take into account photon counting statistics, variation among the 16 dithered frames, and variation among the different aperture measurements (Table 3).…”

Section: Spitzer Datamentioning

confidence: 99%

Composition of KBO (50000) Quaoar

Ore

Barucci

Emery³

et al. 2009

A&A

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Aims. The objective of this work is to investigate the physical properties of objects beyond Neptune -the new frontiers of the Solar System -and in particular to study the surface composition of (50 000) Quaoar, a classical Transneptunian (or Kuiper Belt) object. Because of its distance from the Sun, Quaoar is expected to have preserved, to a degree, its original composition. Our goals are to determine to what degree this is true and to shed light on the chemical evolution of this icy body. Methods. We present new near-infrared (3.6 and 4.5 μm) photometric data obtained with the Spitzer Space Telescope. These data complement high resolution, low signal-to-noise spectroscopic and photometric data obtained in the visible and near-infrared (0.4-2.3 μm) at VLT-ESO and provide an excellent set of constraints in the model calculation process. We perform spectral modeling of the entire wavelength range -from 0.3 to 4.5 μm by means of a code based on the Shkuratov radiative transfer formulation of the slab model. We also attempt to determine the temperature of H 2 O ice making use of the crystalline feature at 1.65 μm.Results. We present a model confirming previous results regarding the presence of crystalline H 2 O and CH 4 ice, as well as C 2 H 6 and organic materials, on the surface of this distant icy body. We attempt a measurement of the temperature and find that stronger constraints on the composition are needed to obtain a precise determination. Conclusions. Model fits indicate that N 2 may be a significant component, along with a component that is bright at λ > 3.3 μm, which we suggest at this time could be amorphous H 2 O ice in tiny grains or thin grain coatings. Irradiated crystalline H 2 O could be the source of small-grained amorphous H 2 O ice. The albedo and composition of Quaoar, in particular the presence of N 2 , if confirmed, make this TNO quite similar to Triton and Pluto.

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“…This produced the measured flux of the satellite in standard flux units. To convert these flux units to geometric albedo, we divided the flux of the satellite by the flux of the Sun given by Colina et al (1996) (λ 2.5 µm) or Smith and Gottlieb (1974) (λ > 2.5 µm) and then multiplied by the quantity R 2 * D 2 /r 2 , where R and D are the heliocentric and geocentric distances of Saturn, respectively, and r is the radius of the satellite. No corrections for solar phase angle were made; all observations were made at small solar phase angles.…”

Section: Appendix a Determination Of Spectral Geometric Albedos Of Tmentioning

confidence: 99%

A spectroscopic study of the surfaces of Saturn's large satellites: HO ice, tholins, and minor constituents

Cruikshank¹,

Owen²,

Ore³

et al. 2005

Icarus

100

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We present spectra of Saturn's icy satellites Mimas, Enceladus, Tethys, Dione, Rhea, and Hyperion, 1.0-2.5 µm, with data extending to shorter (Mimas and Enceladus) and longer (Rhea and Dione) wavelengths for certain objects. The spectral resolution (R = λ/ λ) of the data shown here is in the range 800-1000, depending on the specific instrument and configuration used; this is higher than the resolution (R = 225 at 3 µm) afforded by the Visual-Infrared Mapping Spectrometer on the Cassini spacecraft. All of the spectra are dominated by water ice absorption bands and no other features are clearly identified. Spectra of all of these satellites show the characteristic signature of hexagonal H 2 O ice at 1.65 µm. We model the leading hemisphere of Rhea in the wavelength range 0.3-3.6 µm with the Hapke and the Shkuratov radiative transfer codes and discuss the relative merits of the two approaches to fitting the spectrum. In calculations with both codes, the only components used are H 2 O ice, which is the dominant constituent, and a small amount of tholin (Ice Tholin II). Tholin in small quantities (few percent, depending on the mixing mechanism) appears to be an essential component to give the basic red color of the satellite in the region 0.3-1.0 µm. The quantity and mode of mixing of tholin that can produce the intense coloration of Rhea and other icy satellites has bearing on its likely presence in many other icy bodies of the outer Solar System, both of high and low geometric albedos. Using the modeling codes, we also establish detection limits for the ices of CO 2 (a few weight percent, depending on particle size and mixing), CH 4 (same), and NH 4 OH (0.5 weight percent) in our globally averaged spectra of Rhea's leading hemisphere. New laboratory spectral data for NH 4 OH are presented for the purpose of detection on icy bodies. These limits for CO 2 , CH 4 , and NH 4 OH on Rhea are also applicable to the other icy satellites for which spectra are presented here. The reflectance spectrum of Hyperion shows evidence for a broad, unidentified absorption band centered at 1.75 µm.

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Solar flux and its variations

Cited by 111 publications

References 69 publications

Model Calculations of Solar Spectral Irradiance in the 3.7-μm Band for Earth Remote Sensing Applications

Model Calculations of Solar Spectral Irradiance in the 3.7-μm Band for Earth Remote Sensing Applications

Composition of KBO (50000) Quaoar

A spectroscopic study of the surfaces of Saturn's large satellites: HO ice, tholins, and minor constituents

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