Using a field radiometer to estimate instantaneous sky clearness

Revista Brasileira de Engenharia Agrícola e Ambiental

Souza, Eduardo G.³  Sudduth, Ken A.¹  Scharf, Peter²  Hipple, James. D.² 

[1] USDA, Columbia, EUA;University of Missouri, Columbia, EUA;UNIOESTE, Cascavel

关键词: precision agriculture;    nitrogen management;    reflectance;    cloudRESUMO Medidas da reflectância das folhas das plantas mostram-se promissoras para a aplicação de nitrogênio a taxa variável;    entretanto;    a maioria dos resultados de pesquisa foi obtida ao redor do meio-dia solar e com céu aberto;    porém para aplicações práticas um sistema tem que trabalhar debaixo de céu nublado e fora do meio-dia solar;   

DOI  :  10.1590/S1415-43662006000200018

学科分类：农业科学（综合）

来源: Universidade Federal de Campina Grande * Centro de Ciencias e Tecnologia

【 摘 要 】

Reflectance measurements of crop plants and canopies show promise for guiding within-season, variable-rate nitrogen (N) application. Most research results have been obtained around solar noon with clear skies. However, for practical application, the system must work under cloudy skies or away from solar noon. The objective of this work was to assess the effect of cloud conditions on reflectance measurements of a corn canopy. The approach was to estimate an instantaneous sky clearness index (ICI) which could be used to correct field radiometer data for variations in cloud cover, such that the same reflectance reading would be obtained (and the same N recommendation made) for the same plants regardless of cloud conditions. Readings were taken from morning until night over 11 days with a range of sky conditions (sunny, overcast, partly cloudy). Data from clear days were used to estimate the theoretical expected spectral global radiation incident on a horizontal surface. The ICI was calculated as the ratio between the actual spectral global radiation and the corresponding theoretical global radiation. Analysis of the ICI for each band showed that the influence of cloudiness was different for each band. Thus, the cloud effect could not be compensated by the use of a band ratio or vegetation index.

【 授权许可】

CC BY-NC