Shortwave Flux from Satellite-Measured Radiance: A Theoretical Study over Marine Boundary Layer Clouds

Chambers, L. H.; Wielicki, Bruce A.; Loeb, Norman G.

doi:10.1175/1520-0450(2001)040<2144:sffsmr>2.0.co;2

Cited by 17 publications

(16 citation statements)

References 29 publications

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“…If the illumination effects of bumpy cloud topography exceed the shadowing effects, as might be expected for such a high backscattering angle, an overall increase in the nadir reflectance can occur. While this finding is not particularly surprising, it contrasts with a nadir radiance minimum found in previous studies, attributed to radiative smoothing [e.g., Zuidema and Evans , 1998; Várnai , 2000; Chambers et al , 2001; Iwabuchi and Hayasaka , 2002]. These studies all utilized a Lambertian surface; we produce a similar result when we utilize a Lambertian surface (not shown).…”

Section: Discussionsupporting

confidence: 93%

“…The method outlined by Chambers et al [2001] is followed, with the change that the cloud thickness is known, and the parameter A in L ( z ) = Az , where L ( z ) is the mass of liquid water per unit volume of air, is adjusted so that the optical depth of the column matches the original retrieval. The extinction coefficient depends on height according to β( z ) = 2π(0.001)[ r e ( z )] 2 N , where β, r e , and N denote the volume extinction coefficient in inverse kilometers, the effective radius in microns, and an assumed number concentration of 100 cm −3 , respectively.…”

Section: Monte Carlo Reflectance Simulations Using a Vertically Incrementioning

confidence: 99%

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On the angular radiance closure of tropical cumulus congestus clouds observed by the Multiangle Imaging Spectroradiometer

Zuidema¹,

Davies

Moroney

2003

J. Geophys. Res.

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[1] Monte Carlo reflectance simulations of three tropical cumulus congestus clouds reconstructed from Multiangle Imaging Spectroradiometer (MISR) data are compared to the domain-averaged MISR reflectance measurements. The goal of the comparison is to evaluate the nadir-view pixel cloud optical depth retrievals derived using plane-parallel radiative transfer theory, and the assumptions for vertically distributing the optical depth. Cloud heights are operationally retrieved using a stereo-imaging algorithm. The cloud heights and optical depths are at a 275 m spatial resolution, and for most simulations a vertical resolution of 250 m is applied. Five different but common three-dimensional cloud representations are assessed, using (1) a column vertical-mean volume extinction coefficient (b) value (the reference case), (2) a volume extinction coefficient proportional to the two-thirds power of height (the adiabatic assumption), (3) the adiabatic assumption at a 25 m vertical resolution, (4) a vertical-mean b retrieved from reflectances averaged over a (2.2 km) 2 area, and (5) a vertical-mean b retrieved using off-nadir reflectances. An asymmetry about nadir in the observed reflectance means and skewnesses is not reproduced by any Monte Carlo simulation. The lack of symmetry can be related to differing proportions of unobscured sunlit and shadowed cloudy areas within the different views, even for these cases with viewing angles close to the perpendicular plane. The Monte Carlo simulations do not appear to capture the observed fraction of unobscured sunlit and shadowed cloudy areas, suggesting that radiatively significant cloud variability is occurring at scales smaller than the height field resolution of ±550 m. Results from the Monte Carlo simulation done at a higher vertical resolution are consistent with this. The cases examined also contain a nadir maximum in the observed reflectance skewnesses and a relative maximum for the observed nadir reflectances, attributed to the solar illumination of some optically thick cloud surfaces and to specular reflection pervading through the optically thin cloudy regions. This contrasts with previous modeling results that assume a Lambertian surface.

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Section: Discussionsupporting

confidence: 93%

Section: Monte Carlo Reflectance Simulations Using a Vertically Incrementioning

confidence: 99%

On the angular radiance closure of tropical cumulus congestus clouds observed by the Multiangle Imaging Spectroradiometer

Zuidema¹,

Davies

Moroney

2003

J. Geophys. Res.

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“…Note that the uncertainty values are not necessarily determined by a rigorous analysis of the error because when the algorithm was implemented for CERES production, the error in retrieved properties at a pixel resolution was not well understood quantitatively. For example, although earlier studies thought the error in retrieved cloud fraction and optical thickness depended on solar zenith, viewing, and relative azimuth angles (e.g., Loeb et al 1998;Zuidema and Evans 1998;Chambers et al 2001;Vámai and Marshak 2001;Kato et al 2006), the error also depends on cloud type, which makes the quantitative estimate of instantaneous error extremely difficult. Recent Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat observations provide an opportunity to assess retrieved cloud properties from passive instruments.…”

Section: Input Variable Uncertaintiesmentioning

confidence: 99%

An Algorithm for the Constraining of Radiative Transfer Calculations to CERES-Observed Broadband Top-of-Atmosphere Irradiance

Rose

Rutan

Charlock

et al. 2013

Journal of Atmospheric and Oceanic Technology

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NASA's Clouds and the Earth's Radiant Energy System (CERES) project is responsible for operation and data processing of observations from scanning radiometers on board the Tropical Rainfall Measuring Mission (TRMM), Terra, Aqua, and Suomi National Polar-Orbiting Partnership (NPP) satellites. The clouds and radiative swath (CRS) CERES data product contains irradiances computed using a radiative transfer model for nearly all CERES footprints in addition to top-of-atmosphere (TOA) irradiances derived from observed radiances by CERES instruments. This paper describes a method to constrain computed irradiances by CERES-derived TOA irradiances using Lagrangian multipliers. Radiative transfer model inputs include profiles of atmospheric temperature, humidity, aerosols and ozone, surface temperature and albedo, and up to two sets of cloud properties for a CERES footprint. Those inputs are adjusted depending on predefined uncertainties to match computed TOA and CERES-derived TOA irradiance. Because CERES instantaneous irradiances for an individual footprint also include uncertainties, primarily due to the conversion of radiance to irradiance using anisotropic directional models, the degree of the constraint depends on CERES-derived TOA irradiance as well. As a result of adjustment, TOA computed-minus-observed standard deviations are reduced from 8 to 4 W m"^ for longwave irradiance and from 15 to 6 W m~^ for shortwave irradiance. While agreement of computed TOA with CERES-derived irradiances improves, comparisons with surface observations show that model constrainment to the TOA does not reduce computation bias error at the surface. After constrainment, shortwave down at the surface has an increased bias (standard deviation) of 1% (0.5%) and longwave increases by 0.2% (0.1%). Clear-sky changes are negligible.

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“…The theoretical Part I study aims at obtaining a flux retrieval model to be consistent with the instantaneous TQA flux accuracy of current Earth Radiation Budget (ERB) missions. However, it must be considered that the inversion to flux using theoretical AMD models retrieves large flux bias errors (Chambers et al 2001). Toward the creation of an efficient radiance-toflux conversion, the algorithms developed in Part I utilize the three BBR observation angles simultaneously in the flux inversion.…”

Section: Introductionmentioning

confidence: 99%

Radiative Flux Estimation from a Broadband Radiometer Using Synthetic Angular Models in the EarthCARE Mission Framework. Part II: Evaluation

Domenech

López-Baeza

Donovan

et al. 2012

Journal of Applied Meteorology and Climatology

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The instantaneous top-of-atmosphere (TOA) radiance-to-flux conversion for the broadband radiometer (BBR) on board the Earth Clouds. Aerosols, and Radiation Explorer (EarthCARE) was assessed in Part I of this paper, by developing theoretical angular distribution models (ADMs) specifically designed for the instrument viewing configuration. This paper validates the BBR ADMs by comparing derived flux estimates with flux retrievals obtained from the Clouds and the Earth's Radiant Energy System (CERES) Terra models. A CERES BBR-like database is employed in the assessment, which is an optimum dataset to validate the BBR algorithms and to determine the benefits of the multiangular conversion procedures in the BBR instrument. The validation of theoretical results with empirical data is essential to prepare the conversion algorithms prior to the launch of EarthCARE. This paper demonstrates that the application of a linear combination method is not recommended when outgoing radiances do not follow the response modeled in the radiative transfer calculations. An effective radiance averaged model outperforms all other developed models, in terms of the coefficient of variation of the root-mean-square error, in the validation study of the shortwave (SW) regime (clear sky 1.9%; cloudy 7.1%) while an effective radiance along-track model obtains the best comparisons for the longwave (LW) regime (clear sky 1.4%: cloudy 1.5%). The evaluation of the multiangular models with scenes with high anisotropy shows that multiview flux conversion algorithms can statistically improve CERES ADM results when CERES flux discrepancies of a target are higher than 4 W m"" in the LW domain and SW clear-sky scenes and higher than 20 W m"^ in scenes with cloudy conditions.

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Shortwave Flux from Satellite-Measured Radiance: A Theoretical Study over Marine Boundary Layer Clouds

Cited by 17 publications

References 29 publications

On the angular radiance closure of tropical cumulus congestus clouds observed by the Multiangle Imaging Spectroradiometer

On the angular radiance closure of tropical cumulus congestus clouds observed by the Multiangle Imaging Spectroradiometer

An Algorithm for the Constraining of Radiative Transfer Calculations to CERES-Observed Broadband Top-of-Atmosphere Irradiance

Radiative Flux Estimation from a Broadband Radiometer Using Synthetic Angular Models in the EarthCARE Mission Framework. Part II: Evaluation

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