Estimated Flux Density Research Articles

The PHANGS-AstroSat Atlas of Nearby Star-forming Galaxies

We present the Physics at High Angular resolution in Nearby GalaxieS (PHANGS)-AstroSat atlas, which contains UV imaging of 31 nearby star-forming galaxies captured by the Ultraviolet Imaging Telescope on the AstroSat satellite. The atlas provides a homogeneous data set of far-UV and near-UV maps of galaxies within a distance of 22 Mpc and a median angular resolution of 1.″4 (corresponding to a physical scale between 25 and 160 pc). After subtracting a uniform UV background and accounting for Milky Way extinction, we compare our estimated flux densities to GALEX observations, finding good agreement. We find candidate extended UV disks around the galaxies NGC 6744 and IC 5332. We present the first statistical measurements of the clumping of the UV emission and compare it to the clumping of molecular gas traced with the Atacama Large Millimeter/submillimeter Array (ALMA). We find that bars and spiral arms exhibit the highest degree of clumping, and the molecular gas is even more clumped than the far-UV (FUV) emission in galaxies. We investigate the variation of the ratio of observed FUV to Hα in different galactic environments and kiloparsec-sized apertures. We report that ∼65% of the variation of the log10(FUV/Hα) can be described through a combination of dust attenuation with star formation history parameters. The PHANGS-AstroSat atlas enhances the multiwavelength coverage of our sample, offering a detailed perspective on star formation. When integrated with PHANGS data sets from ALMA, the Very Large Telescope-MUSE, the Hubble Space Telescope, and JWST, it develops our comprehensive understanding of attenuation curves and dust attenuation in star-forming galaxies.

Low-frequency Flux Density Measurements and Pulsars with GHz-peaked Spectra

Abstract We have estimated flux densities of several pulsars from radio interferometric observations mainly at 325 MHz using the Giant Metrewave Radio Telescope. The new observations allowed us to update the spectral nature of the observed pulsars, and in six sources we identified relatively high frequency turnovers, which can be classified as new GHz-peaked spectrum (GPS) pulsars. For such objects the turnover in the spectrum is most likely caused by absorption in the immediate vicinity of the pulsar (or in the interstellar medium). We modeled the turnover spectra using the thermal free–free absorption model and the physical parameters obtained from the fits enabled us to identify the environments that could potentially be responsible for the observed absorption, such as pulsar wind nebulae, supernova remnant nebulae or H ii regions. The discovery of 6 new GPS pulsars brings the total number of such objects to 33 and we discuss the properties of the entire sample.

Meterwavelength Single-pulse Polarimetric Emission Survey. V. Flux Density, Component Spectral Variation, and Emission States

Abstract We present the flux density measurements of the pulsars observed in the Meterwavelength Single-pulse Polarimetric Emission Survey. The average flux densities were estimated in 113 pulsars at two frequencies of 325 and 610 MHz using interferometric imaging. The average profile and single-pulse emission in each pulsar were calibrated using the estimated flux density. We have used the flux-calibrated average profile to study the variation of the spectral index across the emission beam in 21 pulsars where the core, inner cone, and the outer conal components could be clearly identified. The central core component showed a steeper increase in emission at the lower frequency compared with conal emission, with an average difference in spectral index δα core-cone ∼ −0.7 between the core and the conal components in this frequency range. In contrast, the inner conal components had positive difference in their spectral index compared to the outer cones with average difference δα in-out ∼ +0.3. The variation in the spectral index across the pulse window should provide valuable inputs for constraining the radio emission processes. The single-pulse emission showed the presence of emission mode changing in 12 pulsars, with three cases where the phenomenon is being reported for the first time. In addition, we have also detected enhanced emission for short durations or flaring, in parts or across the entire emission window in 14 pulsars. The sudden changes in the emission during mode changing, as well as these bursting states, are unrelated to the emission mechanism and suggest the presence of rapid and repetitive changes during the plasma generation process.

An Arecibo 327 MHz Search for Radio Pulsars and Bursts in the Dwarf Irregular Galaxies Leo A and T

Abstract We have conducted an Arecibo 327 MHz search of two dwarf irregular galaxies in the Local Group, Leo A and T, for radio pulsars and single pulses from fast radio bursts and other giant pulse emitters. We detected no astrophysical signals in this search, and we estimate flux density limits on both periodic and burst emission. Our derived luminosity limits indicate that only the most luminous radio pulsars known in our Galaxy and in the Magellanic Clouds (MCs) would have been detectable in our search if they were at the distances of Leo A and T. Given the much smaller stellar mass content and star formation rates of Leo A and T compared to the Milky Way and the MCs, there are likely to be few (if any) extremely luminous pulsars in these galaxies. It is therefore not surprising that we detected no pulsars in our search.

Discovery of a Steep-spectrum Low-luminosity Pulsar with the Murchison Widefield Array

Abstract We report the discovery of the first new pulsar with the Murchison Widefield Array (MWA), PSR J0036−1033, a long-period (0.9 s) nonrecycled pulsar with a dispersion measure (DM) of 23.1 pc cm−3. It was found after processing only a small fraction (∼1%) of data from an ongoing all-sky pulsar survey. Follow-up observations have been made with the MWA, the upgraded Giant Metrewave Radio Telescope (uGMRT), and the Parkes 64 m telescopes, spanning a frequency range from ∼150 MHz to 4 GHz. The pulsar is faint, with an estimated flux density (S) of ∼1 mJy at 400 MHz and a spectrum , where ν is frequency. The DM-derived distance implies that it is also a low-luminosity source (∼0.1 mJy kpc2 at 1400 MHz). The analysis of archival MWA observations reveals that the pulsar’s mean flux density varies by up to a factor of ∼5–6 on timescales of several weeks to months. By combining MWA and uGMRT data, the pulsar position was determined to arcsecond precision. We also report on polarization properties detected in the MWA and Parkes bands. The pulsar’s nondetection in previous pulsar and continuum imaging surveys, the observed high variability, and its detection in a small fraction of the survey data searched to date, all hint at a larger population of pulsars that await discovery in the southern hemisphere, with the MWA and the future low-frequency Square Kilometre Array.

Comparison Study on Harmonic Loss of MW-Class Wind Generators With HTS Field Winding

This paper investigates the effect of slot-pole combination on harmonic loss such as iron loss and eddy-current loss in wind generators with high-temperature superconductor field winding. In order to study the effect of stator configuration, three wind generators having the same rotor structure but different stators were purposely designed to produce 11 MW. In the analysis, 2-D time-stepped finite element analysis was used to estimate flux density waveforms, and then harmonic iron loss in the stator yoke and rotor eddy-current loss were obtained. From the simulation results, we showed that the harmonic effect on stator iron loss is not significant because magnetic loading by field winding dominates. Meanwhile, we found that the eddy-current loss in the rotor by harmonics of magneto motive force strongly depends on the slot-pole combination.

Improving the reliability of closed chamber methodologies for methane emissions measurement in treatment wetlands

Non-homogeneous mixing of methane (NHM) within closed chambers was studied under laboratory conditions. The experimental set-up consisted of a PVC vented chamber of 5.3 litres of effective volume fitted with a power-adjustable 12 V fan. NHM within the chamber was studied according to fan position (top vs lateral), fan airflow strength (23 vs 80 cubic feet per minute) and the mixing time before sample withdrawal (5, 10, 15 and 20 minutes). The potential bias of methane flux densities caused by NHM was addressed by monitoring the difference between linearly expected and estimated flux densities of ca. 400, ca. 800 and ca. 1,600 mg CH(4).m(-2) d(-1). Methane within the chamber was under non-homogeneous conditions. Accordingly, methane concentrations at the bottom of the chamber were between 20 to 70% higher than those recorded at the middle or top sections of the chamber, regardless of fan position, fan air-flow strength or time before sample withdrawal. NHM led to notable biases on flux density estimation. Accordingly, flux density estimated from top and middle sampling sections were systematically lower (ca. 50%) than those expected. Flux densities estimated from bottom samples were between 10% higher and 25% lower than expected, regardless of the flux density considered.

VLBI imaging of a flare in the Crab nebula: more than just a spot

We report on very long baseline interferometry (VLBI) observations of the radio emission from the inner region of the Crab nebula, made at 1.6 GHz and 5 GHz after a recent high-energy flare in this object. The 5 GHz data have provided only upper limits of 0.4 milli-Jansky (mJy) on the flux density of the pulsar and 0.4 mJy/beam on the brightness of the putative flaring region. The 1.6 GHz data have enabled imaging the inner regions of the nebula on scales of up to ≈ 40′′. The emission from the inner “wisps” is detected for the first time with VLBI observations. A likely radio counterpart (designated “C1”) of the putative flaring region observed with Chandra and HST is detected in the radio image, with an estimated flux density of 0.5 ± 0.3 mJy and a size of 02–06. Another compact feature (“C2”) is also detected in the VLBI image closer to the pulsar, with an estimated flux density of 0.4 ± 0.2 mJy and a size smaller than 02. Combined with the broad-band SED of the flare, the radio properties of C1 yield a lower limit of ≈ 0.5 mG for the magnetic field and a total minimum energy of 1.2 × 1041 erg vested in the flare (corresponding to using about 0.2% of the pulsar spin-down power). The 1.6 GHz observations provide upper limits for the brightness (0.2 mJy/beam) and total flux density (0.4 mJy) of the optical Knot 1 located at 06 from the pulsar. The absolute position of the Crab pulsar is determined, and an estimate of the pulsar proper motion (μα = −13.0 ± 0.2 mas/yr, μδ = + 2.9 ± 0.1 mas/yr) is obtained.

Estimation of the Global 222Rn Flux Density from the Earth's Surface

Global 222Rn flux density distributions with a spatial resolution of 1° in latitude and longitude were estimated for each month in the period of 1979-2007 using an 222Rn exhalation model based on a porous media diffusion theory. This exhalation model calculated the 222Rn flux density as a function of the 226Ra content, soil water saturation, and soil temperature. The influence of the topographical ruggedness of the ground surface on the flux density was also considered in the model. The global average of the flux density during the 29-year period was estimated to be 21.3 mBq m-2 s-1. The annual variation in the globally averaged flux density showed a slight but steady increase since 1999. The seasonal variation in the globally averaged flux density was estimated to range from a minimum of 18.8 mBq m-2 s-1 in March to a maximum of 23.6 mBq m-2 s-1 in September. The regional averages for the annual flux density varied from 8.3 mBq m-2 s-1 for the northern part of North America to 33.5 mBq m-2 s-1 for Australia. The latitudinal distribution of zonally averaged flux density was found to be in good agreement with the latitudinal decline at high latitudes in the Northern Hemisphere. The spatial and temporal variations were caused mainly by variations in the soil water content and soil 226Ra content, but to a lesser extent by the soil temperature. The topographical ruggedness was found to increase the flux density by only 2% globally but by more than 10% in mountainous regions. Atmospheric transport simulations using the estimated flux density as input data showed that the simulated atmospheric 222Rn concentration was substantially lower than that measured at Hachijo Island, implying that the flux density of the present study with topographical ruggedness is still underestimated in the East Asian region.

Estimation of the Global 222Rn Flux Density from the Earth's Surface

Global 222Rn flux density distributions with a spatial resolution of 1° in latitude and longitude were estimated for each month in the period of 1979-2007 using an 222Rn exhalation model based on a porous media diffusion theory. This exhalation model calculated the 222Rn flux density as a function of the 226Ra content, soil water saturation, and soil temperature. The influence of the topographical ruggedness of the ground surface on the flux density was also considered in the model. The global average of the flux density during the 29-year period was estimated to be 21.3 mBq m-2 s-1. The annual variation in the globally averaged flux density showed a slight but steady increase since 1999. The seasonal variation in the globally averaged flux density was estimated to range from a minimum of 18.8 mBq m-2 s-1 in March to a maximum of 23.6 mBq m-2 s-1 in September. The regional averages for the annual flux density varied from 8.3 mBq m-2 s-1 for the northern part of North America to 33.5 mBq m-2 s-1 for Australia. The latitudinal distribution of zonally averaged flux density was found to be in good agreement with the latitudinal decline at high latitudes in the Northern Hemisphere. The spatial and temporal variations were caused mainly by variations in the soil water content and soil 226Ra content, but to a lesser extent by the soil temperature. The topographical ruggedness was found to increase the flux density by only 2% globally but by more than 10% in mountainous regions. Atmospheric transport simulations using the estimated flux density as input data showed that the simulated atmospheric 222Rn concentration was substantially lower than that measured at Hachijo Island, implying that the flux density of the present study with topographical ruggedness is still underestimated in the East Asian region.

7 mm continuum observations of ultra compact HII regions

<i>Aims. <i/>Ultra compact HII (UCHII) regions are indicators of high-mass star formation sites and are distributed mainly in the Galactic plane. They exhibit a broad band spectrum with significant emission between near-IR and radio wavelengths. We intend to investigate the possible contribution of the forthcoming ESA Planck mission to the science of UCHII regions by evaluating the possibility of detecting UCHIIs that are bright in the radio regime.<i>Methods. <i/>We performed new 7 mm observations of a sample of UCHII regions. The observations were designed to acquire high-frequency radio spectra. For each source in our sample, the free-free radio spectrum has been modeled. Along with far-IR measurements, our spectra allow us to estimate the flux densities of the sources in the millimeter and sub-millimeter bands. We extrapolated and summed the ionized-gas (free-free radio emission) and dust (thermal emission) contributions in the afore mentioned wavelength ranges. The possibility of Planck detecting the selected sources can be assessed by comparing the estimated flux densities to the expected sensitivity in each Planck channel. To obtain a realistic estimation of the noise produced by the Galactic emission, the Planck sky model software package was used.<i>Results. <i/>For each target source, from our new 7 mm data and other radio measurements from the literature, important physical parameters such as electron density and their spatial distribution, source geometry and emission measure were derived. We conclude that, in the case of the present sample, located close to the Galactic center, Planck will have a very low detection rate. In contrast, assuming that our sample is representative of the whole UCHII-region population, we derive a very high probability of detecting this kind of source with Planck if located instead close to the anticenter. From the analysis of the ionized-gas properties, we suggest that the selected sample could also be contaminated by other kinds of Galactic objects.

Survey of planetary nebulae at 30 GHz with OCRA-p

We report the results of a survey of 442 planetary nebulae at 30 GHz. The purpose of the survey is to develop a list of planetary nebulae as calibration sources which could be used for high frequency calibration in future. For 41 PNe with sufficient data, we test the emission mechanisms in order to evaluate whether or not spinning dust plays an important role in their spectra at 30 GHz. The 30-GHz data were obtained with a twin-beam differencing radiometer, OCRA-p, which is in operation on the Torun 32-m telescope. Sources were scanned both in right ascension and declination. We estimated flux densities at 30 GHz using a free-free emission model and compared it with our data. The primary result is a catalogue containing the flux densities of 93 planetary nebulae at 30 GHz. Sources with sufficient data were compared with a spectral model of free-free emission. The model shows that free-free emission can generally explain the observed flux densities at 30 GHz thus no other emission mechanism is needed to account for the high frequency spectra.

ASTROMETRY AND ASTROPHYSICS WITH THE SPACE TELESCOPE RADIOASTRON

It is well-known that gravitational lensing is a powerful tool in the investigation of the distribution of matter, including that of dark matter (DM). Typical angular distances between images and typical time scales depend on the gravitational lens masses. For the case of microlensing, angular distances between images or typical astrometric shifts are about 10-5 - 10-6 arcsec. Such an angular resolution will be reached with the space–ground VLBI interferometer, Radioastron. The basic targets for microlensing searches should be bright point-like radio sources at cosmological distances. In this case, an analysis of their variability and a solid determination of microlensing could lead to an estimation of their cosmological mass density. Moreover, one could not exclude the possibility that non-baryonic dark matter could also form microlenses if the corresponding optical depth were high enough. It is known that in gravitationally lensed systems the probability (the optical depth) of observing microlensing is relatively high. Therefore, for example, gravitationally lensed objects, like the CLASS gravitational lens B1600+434, appear to be most suitable to detect astrometric microlensing, since features of photometric microlensing have been detected in these objects. However, to directly resolve these images and to directly detect the apparent motion of the knots, the Radioastron sensitivity would have to be improved, since the estimated flux density is below the sensitivity threshold. Alternatively, they may be observed by increasing an integration time, assuming that a radio source has a typical core–jet structure and microlensing phenomena are caused by the superluminal apparent motions of knots. In the case of a confirmation (or a negation) of claims about microlensing in gravitational lens systems, one can speculate about the microlens contribution to the gravitational lens mass. Astrometric microlensing due Galactic MACHOs is not very important because of low optical depths and long typical time scales. Therefore, the launch of the space interferometer Radioastron will enable the investigation of microlensing in the radio band, giving rise to the possibility of not only resolving microimages but also of observing astrometric microlensing.

Studies of relativistic effects with radioastron space mission

In the review we discuss possible studies of GR phenomena such as gravitational microlensing and shadow analysis with the forthcoming RadioAstron space mission. It is well-known that gravitational lensing is a powerful tool in the investigation of the distribution of matter, including that of dark matter (DM). Typical angular distances between images and typical time scales depend on the gravitational lens masses. For the microlensing, angular distances between images or typical astrometric shifts are about 10-5 ? 10-6 as1. Such an angular resolution will be reached with the space-ground VLBI interferometer, Radioastron. The basic targets for microlensing searches should be bright point-like radio sources at cosmological distances. In this case, an analysis of their variability and a reliable determination of microlensing could lead to an estimation of their cosmological mass density. Moreover, one could not exclude the possibility that non-baryonic dark matter could also form microlenses if the corresponding optical depth were high enough. It is known that in gravitationally lensed systems, the probability (the optical depth) to observe microlensing is relatively high; therefore, for example, such gravitationally lensed objects, like CLASS gravitational lens B1600+434, appear the most suitable to detect astrometric microlensing, since features of photometric microlensing have been detected in these objects. However, to directly resolve these images and to directly detect the apparent motion of the knots, the Radioastron sensitivity would have to be improved, since the estimated flux density is below the sensitivity threshold, alternatively, they may be observed by increasing the integration time, assuming that a radio source has a typical core - jet structure and microlensing phenomena are caused by the superluminal apparent motions of knots. In the case of a confirmation (or a disproval) of claims about microlensing in grav?itational lens systems, one can speculate about the microlens contribution to the gravitational lens mass. Astrometric microlensing due to Galactic Macho's action is not very important because of low optical depths and long typical time scales. Therefore, the launch of the space interferometer Radioastron will give excellent new facilities to investigate microlensing in the radio band, allowing the possibility not only to resolve microimages but also to observe astrometric microlensing. Shadows around supermassive black holes can be detected with the RadioAstron space interferometer. .

Parametrização do método do perfil instantâneo para a determinação da condutividade hidráulica do solo em experimentos com evaporação

A condutividade hidráulica do solo é uma propriedade cuja quantificação é essencial para qualquer estudo que envolva o movimento da água no solo. Os métodos para sua determinação baseados na drenagem interna, como o do perfil instantâneo - MPI, são os mais empregados, restringindo-se à determinação da condutividade hidráulica entre a condição de solo saturado e a umidade na capacidade de campo. Com a finalidade de obter a condutividade hidráulica para menores valores de umidade, propôs-se um método de emprego do MPI com evaporação, apresentando-se o procedimento para a determinação do plano de fluxo zero e estimativa da densidade de fluxo. Demonstrou-se a aplicação do método, obtendo-se resultados de condutividade hidráulica para a camada superficial de um perfil monitorado a partir de um experimento de campo realizado durante um período de 12 dias. A profundidade máxima do plano de fluxo zero estimado foi de aproximadamente 0,50 m. A faixa de umidade obtida variou de 0,25 a 0,21 m³ m-3, valores complementares aos obtidos em experimentos sem evaporação no mesmo local. Os resultados indicaram a viabilidade do método, útil especialmente para se estender à faixa de umidade obtida na camada superficial de tais experimentos.

Quantification of carbon dioxide, methane, nitrous oxide and chloroform emissions over Ireland from atmospheric observations at Mace Head

Flux estimates of CO2, CH4, N2O and CHCl3 over Ireland are inferred from continuous atmospheric records of these species. We use radon-222 (222Rn) as a reference compound to estimate unknown sources of other species. The correlation between each species and 222Rn is calculated for a suite of diurnal events that have been selected in the Mace Head record over the period 1995–1997 to represent air masses exposed to sources over Ireland. We established data selection criteria based on 222Rn and 212Pb concentrations. We estimated flux densities of 12×103 kg CH4 km−2 yr−1, 680 kg N2O km−2 yr−1 and 20 kg CHCl3 km−2 yr−1 for CH4, N2O and CHCl3, respectively. We also inferred flux densities of 250×103 kg C km−2 yr−1 for CO2 during wintertime, and of 760×103 kg C km−2 yr−1 for CO2 during summer night-time. Our CH4 inferred flux compare well with the CORINAIR90 and CORNAIR94 inventories for Ireland. The N2O emission flux we inferred is close to the inventory value by CORINAIR90, but twice the inventory value by CORINAIR94 and EDGAR 2.0. This discrepancy may have been caused by the use of the revised 1996 IPCC guidelines for national greenhouse gas inventories in 1994, which include a new methodology for N2O emissions from agriculture. We carried out the first estimation of CHCl3 emission fluxes over Ireland. This estimation is 4 times larger than the CHCl3 emission fluxes measured close to the Mace Head station over peatlands. Our CHCl3 emission fluxes estimate is consistent with the interpretation of the same data by Ryall (personal communication, 2000), who obtained, using a Lagrangian atmospheric transport model, CHCl3 fluxes of 24±7 kg CHCl31 km−2 yr−1. Our estimates of CO2 emission fluxes during summer night-time and wintertime are close to those estimated from inventories and to one biogeochemical model of heterotrophic respiration.

Respiration in broiler litter slurry surface applied to soil

Respiration in broiler litter slurry that was surface applied to soil was examined for the purpose of determining the feasibility of enriching closed crop canopies with carbon dioxide. An estimated flux density of 1.11 g CO 2 m −2 h −1 was calculated to be required from a ground source to obtain a maximum average increase in photosynthate of 23% for C 3 plants. Litter, as received from the farm, was stored at 24°C for 72 days in a closed container (approximating conditions for deep stack storage). The stored litter was made into a slurry and stored at 24°C in a closed container for 23 days (approximating conditions in a manure storage pond). When stored slurry, inoculated 10% by volume with fresh litter slurry aged for seven days, was applied to soil at the rate of 0.13 ml cm −2 (12,890 l ha −1) an average flux density of 5.32 g CO 2 m −2 h −1 was measured.

Numerical Evaluation of Static-Chamber Measurements of Soil-Atmosphere Gas Exchange: Identification of Physical Processes

The exchange of gases between soil and atmosphere is an important process that affects atmospheric chemistry and therefore climate. The static-chamber method is the most commonly used technique for estimating the rate of that exchange. We examined the method under hypothetical field conditions where diffusion was the only mechanism for gas transport and the atmosphere outside the chamber was maintained at a fixed concentration. Analytical and numerical solutions to the soil gas diffusion equation in one and three dimensions demonstrated that gas flux density to a static chamber deployed on the soil surface was less in magnitude than the ambient exchange rate in the absence of the chamber. This discrepancy, which increased with chamber deployment time and air-filled porosity of soil, is attributed to two physical factors: distortion of the soil gas concentration gradient (the magnitude was decreased in the vertical component and increased in the radial component) and the slow transport rate of diffusion relative to mixing within the chamber. Instantaneous flux density to a chamber decreased continuously with time; steepest decreases occurred so quickly following deployment and in response to such slight changes in mean chamber headspace concentration that they would likely go undetected by most field procedures. Adverse influences of these factors were reduced by mixing the chamber headspace, minimizing deployment time, maximizing the height and radius of the chamber, and pushing the rim of the chamber into the soil. Nonlinear models were superior to a linear regression model for estimating flux densities from mean headspace concentrations, suggesting that linearity of headspace concentration with time was not necessarily a good indicator of measurement accuracy.

Flux Densities at 8·87 GHz of 347 Small-diameter Radio Sources

Flux densities at" 8�87 GHz (A = 3�4 cm) have been determined with the Parkes 64 m telescope for 347 radio sources, using an improved on-off integration method. The sources were selected from the Parkes 2700 MHz catalogue as those having estimated flux densities at 8�87 GHz greater than 0'5 Jy (= 0�5 x 1O- 26 Wm-2 Hz-I) and relatively small angular sizes. A total of 156 of the sources are identified with QSOs and 58 with galaxies, and 133 have not been optically identified. Of the 347 sources 101 have been previously measured at this frequency at Parkes. Some of these repeats were made to check variability and others to compare the flux density scale with that of previous measurements. The estimated accuracy of most of the measurements is � 0�034 Jy (r.m.s.) due to noise and confusion and 3�0 % due to other causes.

Simulation study of geometric shape factor approach to estimating earth emitted flux densities from wide field-of-view radiation measurements

A study was performed on the use of geometric shape factors to estimate Earth-emitted flux densities from radiation measurements with wide field-of-view flat-plate radiometers on satellites. Sets of simulated irradiance measurements were computed for unrestricted and restricted field-of-view detectors. In these simulations, the Earth radiation field was modeled using data from Nimbus 2 and 3. Geometric shape factors were derived and applied to these data to estimate flux densities on global and zonal scales. For measurements at a satellite altitude of 600 km, estimates of zonal flux density were in error 1.0 to 1.2%, and global flux density errors were less than 0.2%. Estimates with unrestricted field-of-view detectors were about the same for Lambertian and non-Lambertian radiation models, but were affected by satellite altitude. The opposite was found for the restricted field-of-view detectors.