Ajuste de modelo de estimação de radiação solar difusa e análise de dados de satélites para predição de evapotranspiração de referência
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Data
2021-05-28
Autores
Gomes Junior, Daniel Gonçalves [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
O modelo de Penman-Monteith é originalmente elaborado por base do fundamento do balanço de energia e da radiação líquida utilizados para avaliar a estimativa da evaporação de água de uma superfície vegetada, fundamentos estes que são aplicados atualmente para obtenção de dados de satélites em estudos de evapotranspiração. Estudos com uso de satélite possuem elevado grau de confiabilidade, isso se dá pelo fato de terem sua base de dados abastecidas de algoritmos atrelados à softwares que, conjuntamente, possuem uma precisa e robusta capacidade de análise e processamento de dados. Apresenta-se neste trabalho um modelo de emissividade atmosférica (εa) em função da fração difusa (KDF) e avaliou-se a eficácia deste modelo para estimar a Rn e a suas aplicações no modelo PM-FAO 56. O modelo proposto (ETo_Rn_KDF) apresentou um valor médio de 2,6 mm da estimativa de ETo com desvio padrão de ±1,2 mm (uma superestimava de 13% em relação à medida), enquanto que o modelo da FAO-56 (ETo_Rn_Allen) apresentou um valor médio de 3,3 mm da estimativa de ETo com desvio padrão de ±1,2 mm (uma superestimava de 40% em relação à medida). Apresentamos um dos primeiros trabalhos de pesquisa para a localidade de estudo (Botucatu-SP, Brasil) que compara medidas realizadas in-situ de evapotranspiração de referência padrão grama obtidas pela técnica de lisimetria de pesagem com dados estimados deste mesmo parâmetro pelo uso de satélites. Foram utilizados dados de dois datasets disponíveis na plataforma Google Earth Engine para comparar valores médios mensais de ETo. Dados de estimativa provenientes do dataset MOD16A2.006 superestimam a medida lisimétrica em 8% (R² = 0,94), o que consideramos como uma aproximação excepcional entre estimativa e medida, enquanto que os dados de estimativa provenientes do dataset FLDAS superestimam a medida em até 33% (R² = 0,90). Observamos que é possível utilizar dados do dataset MOD16A2.006 com elevado grau de confiabilidade
The Penman-Monteith model has its theory originally developed based on the concept of the energy balance and net radiation used to evaluate losses of water vapor to the environment from a vegetated surface, fundamentals that are currently applied to obtain data from satellites in studies of evapotranspiration. Evapotranspiration satelittle based studies are considered to be of great reliability, this is due to the fact that they have their database supplied with algorithms linked to softwares that, together, have a precise and robust data analysis and processing capacity. In this work, we propose an atmospheric emissivity (εa) model as a function of the diffuse fraction (KDF). At this study, we show an evaluation and the effectiveness of this model to estimate Rn and its applications in the PM-FAO 56 model. The proposed model (ETo_Rn_KDF) presented an average ETo estimate value of 2,6 mm with a standard deviation of ±1,2 mm (an overestimation of 13% in relation to the measured ETo), while the FAO-56 model (ETo_Rn_Allen) presented an average ETo estimate value of 3,3 mm with a standard deviation of ±1,2 mm (an overestimation of 40% in relation to the measured ETo). We present one of the first research work for the study site (Botucatu-SP, Brazil) that compares in-situ grass reference evapotranspiration measurements obtained by the weighing lysimetry technique with data estimated from this same parameter by the use of satellites. Data from two datasets available at the Google Earth Engine platform were used to compare monthly average values of ETo. Estimated data from MOD16A2.006 dataset overestimates lysimetric measurements by 8% (R² = 0,94), which we consider to be an exceptional approximation between estimated and measured ETo, whereas the estimated data from the FLDAS dataset overestimates lysimetric measurements by 33% (R² = 0,90). We observed that it is possible to use data from MOD16A2.006 dataset with a high degree of reliability.
The Penman-Monteith model has its theory originally developed based on the concept of the energy balance and net radiation used to evaluate losses of water vapor to the environment from a vegetated surface, fundamentals that are currently applied to obtain data from satellites in studies of evapotranspiration. Evapotranspiration satelittle based studies are considered to be of great reliability, this is due to the fact that they have their database supplied with algorithms linked to softwares that, together, have a precise and robust data analysis and processing capacity. In this work, we propose an atmospheric emissivity (εa) model as a function of the diffuse fraction (KDF). At this study, we show an evaluation and the effectiveness of this model to estimate Rn and its applications in the PM-FAO 56 model. The proposed model (ETo_Rn_KDF) presented an average ETo estimate value of 2,6 mm with a standard deviation of ±1,2 mm (an overestimation of 13% in relation to the measured ETo), while the FAO-56 model (ETo_Rn_Allen) presented an average ETo estimate value of 3,3 mm with a standard deviation of ±1,2 mm (an overestimation of 40% in relation to the measured ETo). We present one of the first research work for the study site (Botucatu-SP, Brazil) that compares in-situ grass reference evapotranspiration measurements obtained by the weighing lysimetry technique with data estimated from this same parameter by the use of satellites. Data from two datasets available at the Google Earth Engine platform were used to compare monthly average values of ETo. Estimated data from MOD16A2.006 dataset overestimates lysimetric measurements by 8% (R² = 0,94), which we consider to be an exceptional approximation between estimated and measured ETo, whereas the estimated data from the FLDAS dataset overestimates lysimetric measurements by 33% (R² = 0,90). We observed that it is possible to use data from MOD16A2.006 dataset with a high degree of reliability.
Descrição
Palavras-chave
Balanço de ondas longas, Google Earth Engine, Penman-Monteith, Saldo de radiação, Net outgoing longwave radiation