Radiation Model for Row Crops: I. Geometric View Factors and Parameter Optimization

Abstract

Row crops with partial cover result in different radiation partitioning to the soil and canopy compared with full cover; however, methods to account for partial cover have not been adequately investigated. The objectives of this study were to: (i) develop geometric view factors to account for the spatial distribution of row crop vegetation; (ii) combine view factors with a widely used vegetation radiation balance model; and (iii) optimize three parameters required by the model that describe leaf angle, visible leaf absorption, and near‐infrared leaf absorption. Measurements of transmitted and reflected shortwave irradiance for corn (Zea mays L.), grain sorghum [Sorghum bicolor (L.) Moench], and cotton (Gossypium hirsutum L.) were used to optimize parameters and evaluate the model. View factors were derived by modeling the crop rows as elliptical hedgerows. The optimized ellipsoid leaf angle parameter, visible leaf absorption, and near‐infrared leaf absorption were 1.0, 0.85, and 0.20 for corn; 1.5, 0.82, and 0.20 for grain sorghum; and 3.0, 0.83, and 0.14 for cotton, respectively. Visible leaf absorption was similar for all crops. Near‐infrared leaf absorption was the same for corn and grain sorghum but less for cotton. The only parameter that changed for each crop species was leaf angle. The optimized parameters for corn and grain sorghum were within the range of values recommended in previous studies, and the leaf angle parameter for cotton agreed with a previous study of cotton leaf angles. All parameters were distinctly identifiable, and no parameter correlation was observed.

Intercomparison of four remote-sensing-based energy balance methods to retrieve surface evapotranspiration and water stress of irrigated fields in semi-arid climate

“…The method used in ICARE considers all radiation exchanges between the two layers (vegetation and bare soil), including transmission and multiple reflections, but it assumes that the vegetation cover is homogeneous. It is not adapted to row crops (see Colaizzi et al, 2012 for recent formulations of net radiation for row crops). As long as FORMOSAT-2 images are available, the method used in this paper seems to be the most accurate for estimating R n independently of the heterogeneity of the surface or regional topographic features.…”

Estimating and Validating Soil Evaporation and Crop Transpiration During the HiWATER-MUSOEXE

“…Moreover, Rn c and Rn s were estimated using the method proposed by Morillas et al [8]; the modifications are described in Colaizzi et al [4], [7]. The formulations are as follows:…”

Interceptação da luz pelo cajueiro

“…em que: Ip -PAR transmitida no ponto P Iq -PAR incidente no ponto Q L -índice de área foliar ao longo da trajetória QP projetada sobre um plano normal à QP K -coeficiente da extinção de luz, considerando K = OPG/sen(β) conforme Colaizzi et al (2012) β -elevação solar O parâmetro L pode ser obtido pela seguinte expressão:…”