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Title: Trigonometric correction factors renders the fAPAR-NDVI relationship from active optical reflectance sensors insensitive to solar elevation angle
Contributor(s): Rahman, Muhammad Moshiur  (author)orcid ; Lamb, David  (author)orcid 
Publication Date: 2016
DOI: 10.1016/j.compag.2015.11.020
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Abstract: The normalized difference vegetation index (NDVI), derived from ground based or satellite borne, passive sensors is often used to estimate the fraction of absorbed photosynthetically active radiation (fAPAR) of a plant canopy. It is well documented that the measured NDVI from passive sensors is affected by the sun and/or view geometry due to the non-Lambertian properties of plant canopies. Despite this the fAPAR-NDVI relationships are often found to be independent of the solar elevation angle (ᶿs) because the ᶿs-dependent absorption of the Red wavelengths within the canopy, which dominates the fAPAR, cancels out the ᶿs-dependency of the NIR scattering which dominates the NDVI measurement. Active optical sensors (AOS), which have their own illuminating light source measure NDVI (NDVI AOS) without any interference of solar geometry. However as fAPAR of a plant canopy does change with solar elevation angle (ᶿs), the fAPAR-NDVIAOS relationship too changes with varying ᶿs. The objective of this study was to explore a correction factor which can eliminate the ᶿs-dependency in fAPAR-NDVIAOS relationship. Data were collected using LightScout quantum bar and CropCircle™ for Tall fescue ('Festuca arundinacea' var. Fletcher) at ᶿs ranging from 40° to 80°. A ᶿs-dependent vegetation index, NDVI*AOS that introduces simple trigonometric correction factors to the measured Red and NIR irradiance for nadir-viewing active optical sensor provides a fAPAR-NDVI relationship that is independent of ᶿs. When the solar elevation angle is introduced this way into the NDVIAOS the fAPAR can then be calculated from the NDVIAOS for any solar elevation angle within the range of 40-80°.
Publication Type: Journal Article
Source of Publication: Computers and Electronics in Agriculture, v.121, p. 43-47
Publisher: Elsevier BV
Place of Publication: Netherlands
ISSN: 1872-7107
Fields of Research (FoR) 2008: 070105 Agricultural Systems Analysis and Modelling
070103 Agricultural Production Systems Simulation
070302 Agronomy
Fields of Research (FoR) 2020: 300207 Agricultural systems analysis and modelling
300205 Agricultural production systems simulation
300403 Agronomy
Socio-Economic Objective (SEO) 2008: 830403 Native and Residual Pastures
830405 Non-Cereal Crops for Silage/Green Feed
Socio-Economic Objective (SEO) 2020: 100503 Native and residual pastures
100504 Non-cereal crops (non-cereal crops for hay/silage/green feed)
Peer Reviewed: Yes
HERDC Category Description: C1 Refereed Article in a Scholarly Journal
Appears in Collections:Journal Article
School of Science and Technology

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