Alam, Muhammad Shahinur; Lamb, David; Rahman, Moshiur M

Author(s)

Alam, Muhammad Shahinur

Lamb, David

Rahman, Moshiur M

Publication Date

2018

Abstract

The estimation of actual crop evapotranspiration (ETc) from any given land cover or crop type is important for irrigation water management and agricultural water consumption analysis. The main parameter used for such estimations is the crop coefficient (Kc). Spectral reflectance indices, such as the normalized difference vegetation index (NDVI) and the crop coefficient of a specific crop or pasture canopy are important indicators of 'vigour', namely the photosynthetic activity and rate of biomass accumulation. Measuring both parameters simultaneously, with a view to understanding how they interact, or for creating optical, surrogate indicators of Kc is very difficult because Kc itself is difficult to measure. In this study a portable enclosed chamber was used to measure ETc of a pasture and subsequently calculated Kc from reference evapotranspiration (ETo) data derived from a nearby automatic weather station (AWS). Calibration of the chamber confirms the suitability of the device to measure the amount of water vapour produced by local plant evapotranspiration, producing a calibration factor (C) close to 1 (C=1.02, R2=0.87). The coincident NDVI values were measured using a portable active optical sensor. In a test involving a pasture (Festuca arundinacea var. Dovey) at two different stages of growth in two consecutive growing seasons, the NDVI and crop coefficients were observed to be strongly correlated (R2=0.80 and 0.77, respectively). A polynomial regression (R2=0.84) was found to be the best fit for the combined, multi-temporal Kc-NDVI relationship. The main advantages of this method include the suitability of operating at a smaller scale (<1 m2), in real time and repeatability.

Citation

Computers and Electronics in Agriculture, v.147, p. 12-17

ISSN

1872-7107

0168-1699

Link

https://hdl.handle.net/1959.11/22884

Publisher

Elsevier BV

Title

A refined method for rapidly determining the relationship between canopy NDVI and the pasture evapotranspiration coefficient

Type of document

Journal Article

Entity Type

Publication

Author(s)	Alam, Muhammad Shahinur Lamb, David Rahman, Moshiur M
Publication Date	2018
Abstract	The estimation of actual crop evapotranspiration (ETc) from any given land cover or crop type is important for irrigation water management and agricultural water consumption analysis. The main parameter used for such estimations is the crop coefficient (Kc). Spectral reflectance indices, such as the normalized difference vegetation index (NDVI) and the crop coefficient of a specific crop or pasture canopy are important indicators of 'vigour', namely the photosynthetic activity and rate of biomass accumulation. Measuring both parameters simultaneously, with a view to understanding how they interact, or for creating optical, surrogate indicators of Kc is very difficult because Kc itself is difficult to measure. In this study a portable enclosed chamber was used to measure ETc of a pasture and subsequently calculated Kc from reference evapotranspiration (ETo) data derived from a nearby automatic weather station (AWS). Calibration of the chamber confirms the suitability of the device to measure the amount of water vapour produced by local plant evapotranspiration, producing a calibration factor (C) close to 1 (C=1.02, R2=0.87). The coincident NDVI values were measured using a portable active optical sensor. In a test involving a pasture (Festuca arundinacea var. Dovey) at two different stages of growth in two consecutive growing seasons, the NDVI and crop coefficients were observed to be strongly correlated (R2=0.80 and 0.77, respectively). A polynomial regression (R2=0.84) was found to be the best fit for the combined, multi-temporal Kc-NDVI relationship. The main advantages of this method include the suitability of operating at a smaller scale (<1 m2), in real time and repeatability.
Citation	Computers and Electronics in Agriculture, v.147, p. 12-17
ISSN	1872-7107 0168-1699
Link	https://hdl.handle.net/1959.11/22884
Publisher	Elsevier BV
Title	A refined method for rapidly determining the relationship between canopy NDVI and the pasture evapotranspiration coefficient
Type of document	Journal Article
Entity Type	Publication

A refined method for rapidly determining the relationship between canopy NDVI and the pasture evapotranspiration coefficient

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