The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform

S. Soulayman - One of the best experts on this subject based on the ideXlab platform.

  • Comments on “Performance analysis of tracked panel according to predicted global radiation. Energy conversion and management 50, (2009) 2029–2034” by Chang T.P.
    Energy Conversion and Management, 2019
    Co-Authors: S. Soulayman, M. Hamoud
    Abstract:

    Abstract Chang [1] proposed a method to determine the performance of a south facing single-axis tracked panel according to global radiation predicted by empirical model where the mathematic expressions appropriate for single-axis tracking system were derived, partially in [1] and in detail in [2]. The presented, in [2], Solar Azimuth Angle, rotation Angle and incidence Angle values are not correct. This incorrectness could have its influence on other calculated values. The present comments discuss this incorrectness, correct the above mentioned errors and discuss the sensitivity of other calculated values on the observed errors.

  • Comments on Solar Azimuth Angle
    Renewable Energy, 2018
    Co-Authors: S. Soulayman
    Abstract:

    Abstract Three appropriate relationships for determining the Solar Azimuth Angle with respect to the south direction were considered for giving some comments on the available algorithms for Solar Azimuth Angle calculation. The application of each of the trigonometric functions (sinγs, cosγs and tanγs, where γs is the Solar Azimuth) for determining γs is discussed with regard to the simplicity and generality. It was found that cosγs could be modified in a very simple way in order to be general in determining the Solar Azimuth Angle all over the year. The modified cosγs was compared with those available in literature formulas and formulations with regard to the generality and simplicity. A comparison with available results is provided.

  • Performance of the east–west oriented single-axis tracked collector
    Energy, 2018
    Co-Authors: S. Soulayman, M. Hammoud
    Abstract:

    Abstract Chang [1] proposed a method to determine the gain of a tracked panel, rotated about a horizontal east-west axis with continuous adjustment to minimize the Angle of incidence, according to three kinds of radiation sources will be considered, i.e. the extraterrestrial radiation, global radiation predicted by empirical models under clear sky situation and global radiation observed in Taichung (φ = 24.2° N), Taiwan. In this article, Chang [1] incorrectly calculated the daily variation of the Solar Azimuth Angle. The mentioned error could have its influence on all other results. The present comments are focused on correcting the calculated Solar Azimuth Angle by Chang [1] and to discuss the sensitivity of other calculated values to this observed error.

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

  • Accounting for the effects of sastrugi in the CERES clear-sky Antarctic shortwave angular distribution models
    Atmospheric Measurement Techniques, 2015
    Co-Authors: J. Corbett
    Abstract:

    Abstract. The Cloud and the Earth's Radiant Energy System (CERES) instruments on NASA's Terra, Aqua and Soumi NPP satellites are used to provide a long-term measurement of Earth's energy budget. To accomplish this, the radiances measured by the instruments must be inverted to fluxes by the use of a scene-type-dependent angular distribution model (ADM). For permanent snow scenes over Antarctica, shortwave (SW) ADMs are created by compositing radiance measurements over the full viewing zenith and Azimuth range. However, the presence of small-scale wind blown roughness features called sastrugi cause the BRDF (bidirectional reflectance distribution function) of the snow to vary significantly based upon the Solar Azimuth Angle and location. This can result in monthly regional biases between −12 and 7.5 Wm−2 in the inverted TOA (top-of-atmosphere) SW flux. The bias is assessed by comparing the CERES shortwave fluxes derived from nadir observations with those from all viewing zenith Angles, as the sastrugi affect fluxes inverted from the oblique viewing Angles more than for the nadir viewing Angles. In this paper we further describe the clear-sky Antarctic ADMs from Su et al. (2015). These ADMs account for the sastrugi effect by using measurements from the Multi-Angle Imaging Spectro-Radiometer (MISR) instrument to derive statistical relationships between radiance from different viewing Angles. We show here that these ADMs reduce the bias and artifacts in the CERES SW flux caused by sastrugi, both locally and Antarctic-wide. The regional monthly biases from sastrugi are reduced to between −5 and 7 Wm−2, and the monthly-mean biases over Antarctica are reduced by up to 0.64 Wm−2, a decrease of 74 %. These improved ADMs are used as part of the Edition 4 CERES SSF (Single Scanner Footprint) data.

  • Accounting for the effects of Sastrugi in the CERES Clear-Sky Antarctic shortwave ADMs
    2015
    Co-Authors: J. Corbett
    Abstract:

    Abstract. The Cloud and Earth's Radiant Energy System (CERES) Instruments on NASA's Terra, Aqua and Soumi-NPP satellites are used to provide a long-term measurement of the Earth's energy budget. To accomplish this, the radiances measured by the instruments must be inverted to fluxes by the use of a scene-type dependent angular distribution model (ADM). For permanent snow scenes over Antarctica, shortwave ADMs are created by compositing radiance measurements over the full viewing zenith and Azimuth range. However, the presence of small-scale wind blown roughness features called sastrugi cause the BRDF of the snow to vary significantly based upon the Solar Azimuth Angle and location. This can result in monthly regional biases as large as ±15 Wm−2 in the inverted TOA SW flux. In this paper we created a set of ADMs that account for the sastrugi effect by using measurements from the Multi-Angle Imaging Spectro-Radiometer (MISR) instrument to derive statistical relationships between radiance from different viewing Angles. These ADMs reduce the monthly regional biases to ±5 Wm−2 and the monthly-mean biases are reduced by up to 50%. These improved ADMs are used as part of the next edition of the CERES data.

M. Hamoud - One of the best experts on this subject based on the ideXlab platform.

Yong Tang - One of the best experts on this subject based on the ideXlab platform.

  • Simulation and Analysis of the Topographic Effects on Snow-Free Albedo over Rugged Terrain
    Remote Sensing, 2018
    Co-Authors: Dalei Hao, Jianguang Wen, Qing Xiao, Xingwen Lin, Baocheng Dou, Dongqin You, Yong Tang
    Abstract:

    Topography complicates the modeling and retrieval of land surface albedo due to shadow effects and the redistribution of incident radiation. Neglecting topographic effects may lead to a significant bias when estimating land surface albedo over a single slope. However, for rugged terrain, a comprehensive and systematic investigation of topographic effects on land surface albedo is currently ongoing. Accurately estimating topographic effects on land surface albedo over a rugged terrain presents a challenge in remote sensing modeling and applications. In this paper, we focused on the development of a simplified estimation method for snow-free albedo over a rugged terrain at a 1-km scale based on a 30-m fine-scale digital elevation model (DEM). The proposed method was compared with the radiosity approach based on simulated and real DEMs. The results of the comparison showed that the proposed method provided adequate computational efficiency and satisfactory accuracy simultaneously. Then, the topographic effects on snow-free albedo were quantitatively investigated and interpreted by considering the mean slope, subpixel aspect distribution, Solar zenith Angle, and Solar Azimuth Angle. The results showed that the more rugged the terrain and the larger the Solar illumination Angle, the more intense the topographic effects were on black-sky albedo (BSA). The maximum absolute deviation (MAD) and the maximum relative deviation (MRD) of the BSA over a rugged terrain reached 0.28 and 85%, respectively, when the SZA was 60° for different terrains. Topographic effects varied with the mean slope, subpixel aspect distribution, SZA and SAA, which should not be neglected when modeling albedo.

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

  • cloud sensitivity studies for stratospheric and lower mesospheric ozone profile retrievals from measurements of limb scattered Solar radiation
    Atmospheric Measurement Techniques, 2009
    Co-Authors: Thiranan Sonkaew, V V Rozanov, C Von Savigny, A Rozanov, Heinrich Bovensmann, J P Burrows
    Abstract:

    Abstract. Clouds in the atmosphere play an important role in reflection, absorption and transmission of Solar radiation and thus affect trace gas retrievals. The main goal of this paper is to examine the sensitivity of stratospheric and lower mesospheric ozone retrievals from limb-scattered radiance measurements to clouds using the SCIATRAN radiative transfer model and retrieval package. The retrieval approach employed is optimal estimation, and the considered clouds are vertically and horizontally homogeneous. Assuming an aerosol-free atmosphere and Mie phase functions for cloud particles, we compute the relative error of ozone profile retrievals in a cloudy atmosphere if clouds are neglected in the retrieval. To access altitudes from the lower stratosphere up to the lower mesosphere, we combine the retrievals in the Chappuis and Hartley ozone absorption bands. We find significant cloud sensitivity of the limb ozone retrievals in the Chappuis bands at lower stratospheric altitudes. The relative error in the retrieved ozone concentrations gradually decreases with increasing altitude and becomes negligible above approximately 40 km. The parameters with the largest impact on the ozone retrievals are cloud optical thickness, ground albedo and Solar zenith Angle. Clouds with different geometrical thicknesses or different cloud altitudes have a similar impact on the ozone retrievals for a given cloud optical thickness value, if the clouds are outside the field of view of the instrument. The effective radius of water droplets has a small influence on the error, i.e., less than 0.5% at altitudes above the cloud top height. Furthermore, the impact of clouds on the ozone profile retrievals was found to have a rather small dependence on the Solar Azimuth Angle (less than 1% for all possible Azimuth Angles). For the most frequent cloud types, the total error is below 6% above 15 km altitude, if clouds are completely neglected in the retrieval. Neglecting clouds in the ozone profile retrievals generally leads to a low bias for a low ground albedo and to a high bias for a high ground albedo, assuming that the ground albedo is well known.

  • Cloud sensitivity studies for stratospheric and lower mesospheric ozone profile retrievals from measurements of limb scattered Solar radiation
    2009
    Co-Authors: Thiranan Sonkaew, V V Rozanov, C Von Savigny, A Rozanov, Heinrich Bovensmann, J P Burrows
    Abstract:

    Abstract. Clouds in the atmosphere play an important role in reflection, absorption and transmission of Solar radiation affecting trace gas retrievals. The main goal of this paper is to examine the sensitivity of stratospheric and lower mesospheric ozone retrievals from limb-scattered radiance measurements to clouds using the SCIATRAN radiative transfer model and retrieval package. Assuming an aerosol-free atmosphere and Mie phase functions for cloud particles, we compute the relative error of ozone profile retrievals in a cloudy atmosphere if clouds are neglected in the retrieval. To access altitudes from the lower stratosphere up to lower mesosphere, we combine the retrievals in the Chappuis and Hartley ozone absorption bands. We find significant cloud sensitivity of the limb ozone retrievals in the Chappuis bands at lower stratospheric altitudes. The relative error in the retrieved ozone concentrations gradually decreases with increasing altitude and becomes negligible above about 40 km. The parameters with the largest impact on the ozone retrievals are cloud optical thickness, ground albedo and Solar zenith Angle. Clouds with different geometrical thicknesses or different cloud altitudes have a similar impact on the ozone retrievals for a given cloud optical thickness value, if the clouds are outside the field of view of the instrument. The effective radius of water droplets has a small influence on the error, i.e., less than 0.5% at altitudes above the cloud top height. Furthermore, the impact of clouds on the ozone profile retrievals was found to have a rather small dependence on the Solar Azimuth Angle (less than 1% for all possible Azimuth Angles). For the most frequent cloud types the total error is below 6% above 15 km altitude, if clouds are completely neglected in the retrieval. Neglecting clouds in the ozone profile retrievals generally leads to a low bias for a low ground albedo and to a high bias for a high ground albedo, assuming that the ground albedo is well known.