Spectral radiative-transfer modeling with minimized computation time by use of a neural-network technique

Schwander, Harry; Kaifel, Anton; Ruggaber, A.; Koepke, Peter

doi:10.1364/ao.40.000331

Cited by 28 publications

(15 citation statements)

References 8 publications

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“…This is done by Radonic1 model developed by Mech and Koepke (2004). The radiances are modeled with STAR, System for Transfer of Atmospheric Radiation (Ruggaber et al, 1994;Schwander et al, 2000), which is known to be of high quality (Koepke et al, 1998). The quality of the model irradiances on vertical surfaces has been corroborated by results of automatic measuring system, Angle SCAanning RAdiometer for determination of erythemally weighted irradiance on TIlted Surfaces (ASCARATIS), that was developed by the Meteorological Institute and the Institute of Outpatient Clinic for Occupational and Environmental Medicine in Munich (Oppenrieder et al, 2004;Mech and Koepke, 2004).…”

Section: Model Resultsmentioning

confidence: 99%

Measurements of UV radiation on rotating vertical plane at the ALOMAR Observatory (69° N, 16° E), Norway, June 2007

et al. 2008

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Abstract. Erythemaly weighted UV and total UV-A irradiance measured at the ALOMAR (Arctic Lidar Observatory for Middle Atmosphere Research; 69 • N, 16 • E) in June 2007 by two Kipp & Zonen UV broadband meters type, UV-S-EA-T, are examined. One unit is mounted on rotating vertical plane and the other is permanently fixed horizontally. The UV broadband meters measure simultaneously to compare UV irradiances on vertical and horizontal planes. The entire range of such relative exposure variations during clearsky and overcast conditions over ALOMAR in the period March-June 2007 is examined using STAR and Radonic1 model (developed at the Meteorological Institute, University of Munich) for various action spectra: erythema, UV-A, and vitamin D 3 . The model and observations support that the daily means of relative exposures are quite stable, i.e., vary within the range 0.4-0.6 with the mean around 0.5 when the averaged intra-day, day-to-day, and seasonal changes of the relative erythemal exposures are considered. It seems that multiplication of the daily mean dose from a broadband meter placed horizontally by the factor of 0.5 gives reasonable estimation of the daily mean exposure on a vertically oriented receiver randomly oriented towards the Sun. The model studies during clear-sky conditions show that the extreme value and daily variability of relative exposure are the highest for UV-A, next for erythemal UV, then for vitamin D 3 weighed UV irradiance. The minima of relative exposure (∼0.20-0.30) are almost the same for all weighting functions. The comparison of model simulations and measurements suggests that specific cloud configuration could lead to significant enhancement of UV exposure of rotating receiver.

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Section: Model Resultsmentioning

confidence: 99%

Measurements of UV radiation on rotating vertical plane at the ALOMAR Observatory (69° N, 16° E), Norway, June 2007

et al. 2008

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“…The model calculations have been carried out for both eclipse and non-eclipse conditions to obtain the variation of various radiative quantities during the eclipse, under real atmospheric conditions but without the presence of clouds. The simulations of the radiative processes in the atmosphere have been performed by an improved version of the radiative transfer model STAR (Schwander et al, 2001). It is based on a one-dimensional radiative transfer algorithm (Nakajima and Tanaka, 1988) that considers absorption and scattering (including multiple scattering) of air molecules, aerosol particles and atmospheric trace gases.…”

Section: Modelling Of the Extraterrestrial Irradiance Spectrum Duringmentioning

confidence: 99%

Effects of total solar eclipse of 29 March 2006 on surface radiation

et al. 2007

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Abstract. Solar irradiance spectral measurements were performed during a total solar eclipse. The spectral effect of the limb darkening to the global, direct irradiance and actinic flux measurements was investigated. This effect leads to wavelength dependent changes in the measured solar spectra showing a much more pronounced decrease in the radiation at the lower wavelengths. Radiative transfer model results were used for the computation of a correction for the total ozone measurements due to the limb darkening. This correction was found too small to explain the large decrease in total ozone column derived from the standard Brewer measurements, which is an artifact in the measured irradiance due to the increasing contribution of diffuse radiation against the decreasing direct irradiance caused by the eclipse. Calculations of the Extraterrestrial spectrum and the effective sun's temperatures, as measured from ground based direct irradiance measurements, showed an artificial change in the calculations of both quantities due to the fact that radiation coming from the visible part of the sun during the eclipse phases differs from the black body radiation described by the Planck's law.

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“…They were able to achieve better results with a much lower computational time using neural networks. Schwander et al (2001) undertook a new approach to reduce the computational time involved in the execution of the radiative transfer model using neural networks. They have used neural network to simulate radiances in UV and visible spectral ranges.…”

Section: Input Layer Output Layermentioning

confidence: 99%

Radiative transfer simulations for the MADRAS imager of Megha-Tropiques

Ramanujam

Balaji

2011

J Earth Syst Sci

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This paper reports the radiative transfer simulations for the passive microwave radiometer onboard the proposed Indian climate research satellite Megha-Tropiques due to be launched in 2011. These simulations have been performed by employing an in-house polarized radiative transfer code for raining systems ranging from depression and tropical cyclones to the Indian monsoon. For the sake of validation and completeness, simulations have also been done for the Tropical Rainfall Measuring Mission (TRMM)'s Microwave Imager (TMI) of the highly successful TRMM mission of NASA and JAXA. The paper is essentially divided into two parts: (a) Radiometer response with specific focus on high frequency channels in both the radiometers is discussed in detail with a parametric study of the effect of four hydrometeors (cloud liquid water, cloud ice, precipitating water and precipitating ice) on the brightness temperatures. The results are compared with TMI measurements wherever possible. (b) Development of a neural network-based fast radiative transfer model is elucidated here. The goal is to speed up the computational time involved in the simulation of brightness temperatures, necessitated by the need for quick and online retrieval strategies. The neural network model uses hydrometeor profiles as inputs and simulates spectral microwave brightness temperature at multiple frequencies as output. A huge database is generated by executing the in-house radiative transfer code for seven different cyclones occurred in North Indian Ocean region during the period 2001-2006. A part of the dataset is used to train the network while the remainder is used for testing purposes. For the purpose of testing, a typical scene from the southwest monsoon rain is also considered. The results obtained are very encouraging and show that the neural network is able to mimic the underlying physics of the radiative transfer simulations with a correlation coefficient of over 99%. Nomenclature a, b, α, γ : constants appearing in modified gamma distribution for hydrometeors B : Planck blackbody function, W/ (m 2 μm sr) CI : cloud ice, g/m 3 CLW : cloud liquid water, g/m 3 H : horizontal polarization I, Q, U, V : Stokes parameters P : scattering (or Mueller) matrix PI : precipitating ice, g/m 3Pw : precipitating water, g/m 3 R r : ground or surface rain rate, mm/h V : vertical polarizationGreek Symbols θ : zenith angle μ : cosine of the zenith angle τ : optical depth φ : azimuthal anglẽ ω : single scattering Albedo

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Spectral radiative-transfer modeling with minimized computation time by use of a neural-network technique

Cited by 28 publications

References 8 publications

Measurements of UV radiation on rotating vertical plane at the ALOMAR Observatory (69° N, 16° E), Norway, June 2007

Measurements of UV radiation on rotating vertical plane at the ALOMAR Observatory (69° N, 16° E), Norway, June 2007

Effects of total solar eclipse of 29 March 2006 on surface radiation

Radiative transfer simulations for the MADRAS imager of Megha-Tropiques

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