Evaluation of sunshine duration from cloud data in Egypt

Robaa, S. M.

doi:10.1016/j.energy.2007.12.001

Cited by 57 publications

(39 citation statements)

References 34 publications

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“…Human observations were the first method of cloud coverage determination. Observers classify clouds according to the subjective view of shape and appearance (Robaa, 2008) and estimate sky coverage. During the last years more and more of these human-based observations were replaced by ground-based automated instruments to obtain a higher consistency in cloud coverage estimations (Orsini et al, 2002;Dürr and Philipona, 2004).…”

Section: A Werkmeister Et Al: Comparing Cloud Coverage -A Case Studymentioning

confidence: 99%

Comparing satellite- to ground-based automated and manual cloud coverage observations – a case study

et al. 2015

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Abstract. In this case study we compare cloud fractional cover measured by radiometers on polar satellites (AVHRR) and on one geostationary satellite (SEVIRI) to ground-based manual (SYNOP) and automated observations by a cloud camera (Hemispherical Sky Imager, HSI). These observations took place in Hannover, Germany, and in Lauder, New Zealand, over time frames of 3 and 2 months, respectively.Daily mean comparisons between satellite derivations and the ground-based HSI found the deviation to be 6 ± 14 % for AVHRR and 8 ± 16 % for SEVIRI, which can be considered satisfactory. AVHRR's instantaneous differences are smaller (2 ± 22 %) than instantaneous SEVIRI cloud fraction estimates (8 ± 29 %) when compared to HSI due to resolution and scenery effect issues. All spaceborne observations show a very good skill in detecting completely overcast skies (cloud cover ≥ 6 oktas) with probabilities between 92 and 94 % and false alarm rates between 21 and 29 % for AVHRR and SEVIRI in Hannover, Germany. In the case of a clear sky (cloud cover lower than 3 oktas) we find good skill with detection probabilities between 72 and 76 %. We find poor skill, however, whenever broken clouds occur (probability of detection is 32 % for AVHRR and 12 % for SEVIRI in Hannover, Germany).In order to better understand these discrepancies we analyze the influence of algorithm features on the satellite-based data. We find that the differences between SEVIRI and HSI cloud fractional cover (CFC) decrease (from a bias of 8 to almost 0 %) with decreasing number of spatially averaged pixels and decreasing index which determines the cloud coverage in each "cloud-contaminated" pixel of the binary map. We conclude that window size and index need to be adjusted in order to improve instantaneous SEVIRI and AVHRR estimates. Due to its automated operation and its spatial, temporal and spectral resolution, we recommend as well that more automated ground-based instruments in the form of cloud cameras should be installed as they cover larger areas of the sky than other automated ground-based instruments. These cameras could be an essential supplement to SYNOP observation as they cover the same spectral wavelengths as the human eye.

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Section: A Werkmeister Et Al: Comparing Cloud Coverage -A Case Studymentioning

confidence: 99%

Comparing satellite- to ground-based automated and manual cloud coverage observations – a case study

et al. 2015

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“…(1984) apresentaram os valores desses coeficientes encontrados em 120 trabalhos científicos de diversas regiões da Terra e constataram que condições geográficas e climáticas podem modificar os valores para agrupamentos anuais, sazonais e mensais, com uma faixa de variação entre 0,14 e 0,35 para "a" e de 0,35 a 0,79 para "b", corroborando com os valores encontrados. Esta grande faixa de variação decorre da dependência da latitude, altitude, época do ano, mudanças no tipo e espessura de nuvens e concentração de poluentes (Almorox et al, 2005;Rensheng et al, 2006;Robaa, 2008).…”

Section: Resultsunclassified

“…A medida da radiação solar foi, durante muito tempo, difícil e onerosa, em razão dos custos elevados limitarem as aquisições de radiômetros, restringindo seu uso aos centros de pesquisa (Blanco & Sentelhas, 2002;Tiba et al 2005;Turco & Rizatti, 2006;Rensheng et al, 2006;Robaa, 2008;Moradi, 2009;Carvalho et al 2011); assim, muitos modelos estatísticos e/ou paramétricos de estimativa foram desenvolvidos com base em parâmetros meteorológicos, geográficos, atmosféricos e astronômicos. Neste contexto, Angströn (1924) propôs um modelo estatístico linear, que foi simplificado por Prescott (1940), em função das dificuldades de medidas em dias com ausência total de nuvens e que correlaciona a transmissividade atmosférica da radiação solar global (K T d ) (razão entre a radiação global e a radiação no topo da atmosfera) e a razão de insolação (n/N) (razão entre o brilho solar e o fotoperíodo).…”

Section: Introductionunclassified

Estimativas da radiação global incidente em superfícies inclinadas com base na razão de insolação

Souza

Escobedo

2013

Agraria

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“…The prediction quality of regression equations was also verified on the basis of independent material which was not directly used during their formation. In the case of four years : 2006, 2007, 2008 and 2009 for the whole country (a mean of all COBORU stations), the following indexes were determined: mean bias error (MBE), mean absolute bias error (MABE) and root mean square error (RMSE) (Robaa, 2008;Bakirci, 2009).…”

Section: Methodsmentioning

confidence: 99%

Risk of field cultivation of pickling cucumber caused by unfavorable sunshine duration conditions

Kalbarczyk

2011

Sci. agric. (Piracicaba, Braz.)

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Solar energy, accessible to plants during sunshine from the sunrise to the sunset is of key importance in productivity of agrocenoses. The aim of the work was to determine risk of pickling cucumber cultivation caused by an unfavorable course of sunshine duration in Poland on the basis of a 40-year research period . The research into the subject was undertaken due to frequent occurrence of sunshine deficiency in Poland and its high temporal and spatial variability. Effect of solar conditions described by sunshine duration in the five development stages on the quantity of the total and marketable yield of cucumber with consideration of a linear trend of an independent variable was determined by means of multiple regression analysis. The accuracy of the equations was evaluated on the basis of, among other things, determination coefficient, average relative forecast error and the indexes: mean bias error (MBE), mean absolute bias error (MABE) and root mean square error (RMSE). Cucumber (Cucumis sativus L.) yield was confirmed for the period from the end of emergence to the beginning of flowering and from the beginning of harvesting to the end of harvesting. Cucumber yield was lower by 18% than the multiannual average in the years 1966-2005 every 1.5-2 years -in the case of the occurrence of the shortage in the period from the end of emergence to the beginning of flowering and by 12-15% every 2-3 years in the period from the beginning of harvesting to the end of harvesting. In four years, out of the 40 considered ones, simultaneously in both cucumber development stages, unfavorable solar conditions occurred, causing reduction by at least 5% in the total yield of the plant in Poland, and in three years -the marketable yield. Key words: development, growth, reduction in yield, solar conditions Risco do cultivo de campo de pepino decapado causado por condições desfavoráveis de duração de brilho solar RESUMO: A disponibilidade de energia solar para as plantas desde o nascer ao por do sol é de fundamental importância para todo agronegócio. O objetivo deste trabalho foi determinar o risco da produção de pepino (Cucumis sativus L.) decapado causado pelo curso desfavorável de duração da radiação solar na Polônia, baseado em um período de 40 anos de pesquisa . A pesquisa foi realizada pelo fato da ocorrência frequente de deficiência de insolação na Polônia e sua alta variabilidade temporal e espacial. O efeito das condições solares descritas pela duração da insolação foi estudado em relação às produtividades total e comerciável de pepino, considerando uma tendência linear de uma variável independente. A precisão das equações foi avaliada com base no coeficiente de determinação, erro médio relativo de precisão e índices: erro médio de bias, erro médio absoluto de bias e raiz do erro médio quadrado. A produtividade foi analisada a partir da emergência até o início do florescimento e do inicio ao fim da colheita. A produtividade de pepino foi 18% menor em relação a media multianual dos anos 1966-2005 cada 1,5-2 anos -n...

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Evaluation of sunshine duration from cloud data in Egypt

Cited by 57 publications

References 34 publications

Comparing satellite- to ground-based automated and manual cloud coverage observations – a case study

Comparing satellite- to ground-based automated and manual cloud coverage observations – a case study

Estimativas da radiação global incidente em superfícies inclinadas com base na razão de insolação

Risk of field cultivation of pickling cucumber caused by unfavorable sunshine duration conditions

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