Relationship between photosynthetically active radiation and global radiation in Petrolina and Brasília, Brazil

Carlos A. C. dos Santos,Bernardo B. da Silva,Lady L. M. Custódio

doi:10.1590/1807-1929/agriambi.v25n9p612-619

Carlos A. C. dos Santos, Bernardo B. da Silva + Show 1 more

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https://doi.org/10.1590/1807-1929/agriambi.v25n9p612-619

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Abstract

ABSTRACT Photosynthetically active radiation (PAR) comprises the spectral range of global solar radiation (Rs) that is highly related to vegetation productivity. The study aimed to evaluate the relationship between PAR and Rs in Petrolina, PE, and Brasília, DF, Brazil, with data measured in 2011 and 2013 at two stations of the Sistema Nacional de Organização de Dados Ambientais located in Petrolina, PE and Brasília, DF, Brazil, and the obtained models were evaluated using the measurements of 2014. It was verified that the PAR, in instantaneous values (μmol m-2 s-1), can be estimated at 2.31 times the Rs (W m-2) measured in Petrolina, while for daily values of PAR (MJ m-2) is equal to 50% of Rs (MJ m-2). In Brasília, PAR (μmol m-2 s-1) is 2.05 times the Rs (W m-2) and, in daily values, equal to 44% of Rs (MJ m-2). The variability of the PAR/Rs ratio followed the local variations of clearness index (Kt) and Rs. The models presented an adequate performance based on statistical indices mean absolute error, mean relative error, and root mean square error and can be used to estimate PAR.

Highlights

Material and MethodsPhotosynthetically active radiation (PAR) comprises the ranging of the electromagnetic spectrum from 400 to 700 nm
The study aimed to evaluate the relationship between PAR and radiação solar global (Rs) in Petrolina, PE, and Brasília, DF, Brazil, with data measured in 2011 and 2013 at two stations of the Sistema Nacional de Organização de Dados Ambientais located in Petrolina, PE and Brasília, DF, Brazil, and the obtained models were evaluated using the measurements of 2014
Tsubo & Walker (2005), in studies that consider PAR restricted to the spectral range from 400 to 700 nm, the PAR/Rs ratio ranges from a minimum of 0.41 (Papaioannou et al, 1996) to 0.52 (Kvifte et al, 1983)

Summary

Introduction

Material and MethodsPhotosynthetically active radiation (PAR) comprises the ranging of the electromagnetic spectrum from 400 to 700 nm. Its importance is widely recognized, PAR is usually not measured in the weather station networks in Brazil and worldwide. To overcome this problem, researchers use different PAR estimation techniques, among which the most used technique to obtain PAR is through simple linear regression with global solar radiation (Rs) (Al-Shooshan, 1997; Jacovides et al, 2007; Steidle Neto et al, 2008; Escobedo et al, 2009; Galvani, 2009; Escobedo et al, 2011; Wang et al, 2014; Pashiardis et al, 2017; Chukwujindu et al, 2018). When considering the range from 300 to 700 nm, the PAR/Rs ratio ranges from 0.43 (Papaioannou et al, 1993) to 0.57 (Kvifte et al, 1983)

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