The Experts below are selected from a list of 126 Experts worldwide ranked by ideXlab platform

Fulvia Villani - One of the best experts on this subject based on the ideXlab platform.

  • Multiple Processor Version of a Monte Carlo code for photon transport in turbid media
    Computer Physics Communications, 2000
    Co-Authors: Alberto Colasanti, Giovanni Guida, Annamaria Kisslinger, Raffaele Liuzzi, Maria Quarto, Patrizia Riccio, Giuseppe Roberti, Fulvia Villani
    Abstract:

    Abstract Although Monte Carlo (MC) simulations represent an accurate and flexible tool to study the photon transport in strongly scattering media with complex geometrical topologies, they are very often infeasible because of their very high computation times. Parallel computing, in principle very suitable for MC approach because it consists in the repeated application of the same calculations to unrelated and superposing events, offers a possible approach to overcome this problem. It was developed an MC multiple Processor code for optical and IR photon transport which was run on the parallel Processor computer CRAY-T3E (128 DEC Alpha EV5 nodes, 600 Mflops) at CINECA (Bologna, Italy). The comparison between single Processor and multiple Processor runs for the same tissue models shows that the parallelization reduces the computation time by a factor of about N , where N is the number of used Processors. This means a computation time reduction by a factor ranging from about 10 2 (as in our case where 128 Processors are available) up to about 10 3 (with the most powerful parallel computers with 1024 Processors). This reduction could make feasible MC simulations till now impracticable. The scaling of the execution time of the parallel code, as a function of the values of the main input parameters, is also evaluated.

  • Multiple Processor Version of a Monte Carlo code for photon transport in turbid media
    Computer Physics Communications, 2000
    Co-Authors: Alberto Colasanti, Giovanni Guida, Annamaria Kisslinger, Raffaele Liuzzi, Maria Quarto, Patrizia Riccio, Giuseppe Roberti, Fulvia Villani
    Abstract:

    Although Monte Carlo (MC) simulations represent an accurate and flexible tool to study the photon transport in strongly scattering media with complex geometrical topologies, they are very often infeasible because of their very high computation Limes. Parallel computing, in principle very suitable fur MC approach because it consists in the repeated application of the same calculations to unrelated and superposing events, offers a possible approach to overcome this problem. It was developed an MC multiple Processor code for optical and IR photon transport which was run on the parallel Processor computer CRAY-T3E (128 DEC Alpha EV5 nodes, 600 Mflops) at CINCA (Bologna, Italy). The comparison between single Processor and multiple Processor runs for the same tissue models shows that the parallelization reduces the computation time by a factor of about N, where N is the number of used Processors. This means a computation time reduction by a factor ranging from about 10(2) (as in our case where 128 Processors are available) up to about 10(3) (with the most powerful parallel computers with 1024 Processors). This reduction could make feasible MC simulations till now impracticable. The scaling of the execution time of the parallel code, as a function of the values of the main input parameters, is also evaluated

Alberto Colasanti - One of the best experts on this subject based on the ideXlab platform.

  • Multiple Processor Version of a Monte Carlo code for photon transport in turbid media
    Computer Physics Communications, 2000
    Co-Authors: Alberto Colasanti, Giovanni Guida, Annamaria Kisslinger, Raffaele Liuzzi, Maria Quarto, Patrizia Riccio, Giuseppe Roberti, Fulvia Villani
    Abstract:

    Abstract Although Monte Carlo (MC) simulations represent an accurate and flexible tool to study the photon transport in strongly scattering media with complex geometrical topologies, they are very often infeasible because of their very high computation times. Parallel computing, in principle very suitable for MC approach because it consists in the repeated application of the same calculations to unrelated and superposing events, offers a possible approach to overcome this problem. It was developed an MC multiple Processor code for optical and IR photon transport which was run on the parallel Processor computer CRAY-T3E (128 DEC Alpha EV5 nodes, 600 Mflops) at CINECA (Bologna, Italy). The comparison between single Processor and multiple Processor runs for the same tissue models shows that the parallelization reduces the computation time by a factor of about N , where N is the number of used Processors. This means a computation time reduction by a factor ranging from about 10 2 (as in our case where 128 Processors are available) up to about 10 3 (with the most powerful parallel computers with 1024 Processors). This reduction could make feasible MC simulations till now impracticable. The scaling of the execution time of the parallel code, as a function of the values of the main input parameters, is also evaluated.

  • Multiple Processor Version of a Monte Carlo code for photon transport in turbid media
    Computer Physics Communications, 2000
    Co-Authors: Alberto Colasanti, Giovanni Guida, Annamaria Kisslinger, Raffaele Liuzzi, Maria Quarto, Patrizia Riccio, Giuseppe Roberti, Fulvia Villani
    Abstract:

    Although Monte Carlo (MC) simulations represent an accurate and flexible tool to study the photon transport in strongly scattering media with complex geometrical topologies, they are very often infeasible because of their very high computation Limes. Parallel computing, in principle very suitable fur MC approach because it consists in the repeated application of the same calculations to unrelated and superposing events, offers a possible approach to overcome this problem. It was developed an MC multiple Processor code for optical and IR photon transport which was run on the parallel Processor computer CRAY-T3E (128 DEC Alpha EV5 nodes, 600 Mflops) at CINCA (Bologna, Italy). The comparison between single Processor and multiple Processor runs for the same tissue models shows that the parallelization reduces the computation time by a factor of about N, where N is the number of used Processors. This means a computation time reduction by a factor ranging from about 10(2) (as in our case where 128 Processors are available) up to about 10(3) (with the most powerful parallel computers with 1024 Processors). This reduction could make feasible MC simulations till now impracticable. The scaling of the execution time of the parallel code, as a function of the values of the main input parameters, is also evaluated

J. P. Burrows - One of the best experts on this subject based on the ideXlab platform.

  • Validation of SCIAMACHY top-of-atmosphere reflectance for aerosol remote sensing using MERIS L1 data
    Atmospheric Chemistry and Physics, 2007
    Co-Authors: W. Von Hoyningen-huene, A. A. Kokhanovsky, M. W. Wuttke, M. Buchwitz, S. Noël, K. Gerilowski, J. P. Burrows, B. Latter, R. Siddans, B. J. Kerridge
    Abstract:

    Aerosol remote sensing is very much dependent on the accurate knowledge of the top-of-atmosphere (TOA) reflectance measured by a particular instrument. The status of the calibration of such an instrument is reflected in the quality of the aerosol retrieval. Current data of the SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) instrument (operated with the data Processor Version 5 and earlier) give too small values of the TOA reflectance, compared e.g. to data from MERIS (Medium Resolution Imaging Spectrometer), both operating on ENVISAT (ENVIronmental SATellite). This effect causes retrievals of wrong aerosol optical thickness and disables the processing of aerosol parameters. From an inter-comparison of MERIS and SCIAMACHY TOA reflectance, for collocated scenes correction factors are derived to improve the insufficient SCIAMACHY L1 data calibration for data obtained with the Processor 5 for the purpose of aerosol remote sensing. The corrected reflectance has been used for tests of remote sensing of the aerosol optical thickness by the BAER (Bremen AErosol Retrieval) approach using SCIAMACHY data.

  • Pole-to-pole validation of GOME WFDOAS total ozone with groundbased data
    Atmospheric Chemistry and Physics, 2005
    Co-Authors: M Weber, K Bramstedt, L. N. Lamsal, M. Coldewey-egbers, J. P. Burrows
    Abstract:

    This paper summarises the validation of GOME total ozone retrieved using the Weighting Function Differential Optical Absorption Spectroscopy (WFDOAS) algorithm Version 1.0. This algorithm has been described in detail in a companion paper by Coldewey-Egbers et al. (2005). Compared to the operational GDP (GOME Data Processor) V3, several improvements to the total ozone retrieval have been introduced that account for the varying ozone dependent contribution to rotational Raman scattering, includes a new cloud scheme, and uses the GOME measured effective albedo in the retrieval. In this paper the WFDOAS results have been compared with selected ground-based measurements from the WOUDC (World Ozone and UV Radiation Data Centre) that collects total ozone measurements from a global network of stations covering all seasons. From the global validation excellent agreement between WFDOAS and ground data was observed. The agreement lies within ±1%, and very little seasonal variations in the differences are found. In the polar regions and at high solar zenith angles, however, a positive bias varying between 5 and 8% is found near the polar night period. As a function of solar zenith angle as well as of the retrieved total ozone, the WFDOAS differences to ground polar data, however, show a much weaker dependence as compared to the operational GOME Data Processor Version 3 of GOME that represents a significant improvement. Very few stations carry out simultaneous measurements by Brewer and Dobson spectrometers over an extended period (three years or more). Simultaneous Brewer and Dobson measurements from Hradec Kralove, Czech Republic (50.2N, 15.8E) and Hohenpeissenberg, Germany (47.8N, 11.0E) covering the period 1996-1999 have been compared with our GOME results. Agreement with Brewers are generally better than with the simultaneous Dobson measurements and this may be explained by the neglect of stratospheric (ozone) temperature correction in the standard ozone retrieval from the ground.

  • comparison of total ozone from the satellite instruments gome and toms with measurements from the dobson network 1996 2000
    Atmospheric Chemistry and Physics, 2002
    Co-Authors: K Bramstedt, Diego Loyola, Werner Thomas, J F Gleason, Astrid Bracher, M Weber, J. P. Burrows
    Abstract:

    Over the last 3 decades, satellite data have been used to monitor long-term global changes in stratospheric ozone. The TOMS series (1978-present) and GOME (1995-present) are two very important instruments in this context. In this paper, TOMS total ozone and three approaches to derive total ozone from GOME measurements are validated with ground-based Dobson network data. Beyond the operational products of both instruments, e.g. TOMS Version 7 and GOME Data Processor Version 2.7, total ozone is calculated by integrating FURM ozone profiles and by applying the TOMS algorithm to the GOME spectra. All algorithms show in general good agreement with ground-based measurements. The operational GOME total ozone shows seasonal variations, most likely introduced by difficulties in the derivation of airmass factors, which convert measured slant columns into vertical columns. The TOMS algorithm estimates on average 2% higher total ozone in the southern hemisphere than in the northern for both instruments as compared to the ground-based data, indicating that the source of the observed hemispheric differences is in the TOMS algorithm. Both instruments show aging effects in 2000, leading to enhanced variability in the ozone column differences with respect to Dobson data. In addition, the integrated GOME ozone profiles and the TOMS algorithm applied to GOME data show larger mean deviations in 2000.

Giuseppe Roberti - One of the best experts on this subject based on the ideXlab platform.

  • Multiple Processor Version of a Monte Carlo code for photon transport in turbid media
    Computer Physics Communications, 2000
    Co-Authors: Alberto Colasanti, Giovanni Guida, Annamaria Kisslinger, Raffaele Liuzzi, Maria Quarto, Patrizia Riccio, Giuseppe Roberti, Fulvia Villani
    Abstract:

    Abstract Although Monte Carlo (MC) simulations represent an accurate and flexible tool to study the photon transport in strongly scattering media with complex geometrical topologies, they are very often infeasible because of their very high computation times. Parallel computing, in principle very suitable for MC approach because it consists in the repeated application of the same calculations to unrelated and superposing events, offers a possible approach to overcome this problem. It was developed an MC multiple Processor code for optical and IR photon transport which was run on the parallel Processor computer CRAY-T3E (128 DEC Alpha EV5 nodes, 600 Mflops) at CINECA (Bologna, Italy). The comparison between single Processor and multiple Processor runs for the same tissue models shows that the parallelization reduces the computation time by a factor of about N , where N is the number of used Processors. This means a computation time reduction by a factor ranging from about 10 2 (as in our case where 128 Processors are available) up to about 10 3 (with the most powerful parallel computers with 1024 Processors). This reduction could make feasible MC simulations till now impracticable. The scaling of the execution time of the parallel code, as a function of the values of the main input parameters, is also evaluated.

  • Multiple Processor Version of a Monte Carlo code for photon transport in turbid media
    Computer Physics Communications, 2000
    Co-Authors: Alberto Colasanti, Giovanni Guida, Annamaria Kisslinger, Raffaele Liuzzi, Maria Quarto, Patrizia Riccio, Giuseppe Roberti, Fulvia Villani
    Abstract:

    Although Monte Carlo (MC) simulations represent an accurate and flexible tool to study the photon transport in strongly scattering media with complex geometrical topologies, they are very often infeasible because of their very high computation Limes. Parallel computing, in principle very suitable fur MC approach because it consists in the repeated application of the same calculations to unrelated and superposing events, offers a possible approach to overcome this problem. It was developed an MC multiple Processor code for optical and IR photon transport which was run on the parallel Processor computer CRAY-T3E (128 DEC Alpha EV5 nodes, 600 Mflops) at CINCA (Bologna, Italy). The comparison between single Processor and multiple Processor runs for the same tissue models shows that the parallelization reduces the computation time by a factor of about N, where N is the number of used Processors. This means a computation time reduction by a factor ranging from about 10(2) (as in our case where 128 Processors are available) up to about 10(3) (with the most powerful parallel computers with 1024 Processors). This reduction could make feasible MC simulations till now impracticable. The scaling of the execution time of the parallel code, as a function of the values of the main input parameters, is also evaluated

Patrizia Riccio - One of the best experts on this subject based on the ideXlab platform.

  • Multiple Processor Version of a Monte Carlo code for photon transport in turbid media
    Computer Physics Communications, 2000
    Co-Authors: Alberto Colasanti, Giovanni Guida, Annamaria Kisslinger, Raffaele Liuzzi, Maria Quarto, Patrizia Riccio, Giuseppe Roberti, Fulvia Villani
    Abstract:

    Abstract Although Monte Carlo (MC) simulations represent an accurate and flexible tool to study the photon transport in strongly scattering media with complex geometrical topologies, they are very often infeasible because of their very high computation times. Parallel computing, in principle very suitable for MC approach because it consists in the repeated application of the same calculations to unrelated and superposing events, offers a possible approach to overcome this problem. It was developed an MC multiple Processor code for optical and IR photon transport which was run on the parallel Processor computer CRAY-T3E (128 DEC Alpha EV5 nodes, 600 Mflops) at CINECA (Bologna, Italy). The comparison between single Processor and multiple Processor runs for the same tissue models shows that the parallelization reduces the computation time by a factor of about N , where N is the number of used Processors. This means a computation time reduction by a factor ranging from about 10 2 (as in our case where 128 Processors are available) up to about 10 3 (with the most powerful parallel computers with 1024 Processors). This reduction could make feasible MC simulations till now impracticable. The scaling of the execution time of the parallel code, as a function of the values of the main input parameters, is also evaluated.

  • Multiple Processor Version of a Monte Carlo code for photon transport in turbid media
    Computer Physics Communications, 2000
    Co-Authors: Alberto Colasanti, Giovanni Guida, Annamaria Kisslinger, Raffaele Liuzzi, Maria Quarto, Patrizia Riccio, Giuseppe Roberti, Fulvia Villani
    Abstract:

    Although Monte Carlo (MC) simulations represent an accurate and flexible tool to study the photon transport in strongly scattering media with complex geometrical topologies, they are very often infeasible because of their very high computation Limes. Parallel computing, in principle very suitable fur MC approach because it consists in the repeated application of the same calculations to unrelated and superposing events, offers a possible approach to overcome this problem. It was developed an MC multiple Processor code for optical and IR photon transport which was run on the parallel Processor computer CRAY-T3E (128 DEC Alpha EV5 nodes, 600 Mflops) at CINCA (Bologna, Italy). The comparison between single Processor and multiple Processor runs for the same tissue models shows that the parallelization reduces the computation time by a factor of about N, where N is the number of used Processors. This means a computation time reduction by a factor ranging from about 10(2) (as in our case where 128 Processors are available) up to about 10(3) (with the most powerful parallel computers with 1024 Processors). This reduction could make feasible MC simulations till now impracticable. The scaling of the execution time of the parallel code, as a function of the values of the main input parameters, is also evaluated