Estimation of Actual Crop Coefficients Using Remotely Sensed Vegetation Indices and Soil Water Balance Modelled Data

Isabel Pôças,Paula Paredes,Teresa Paço,Mário Cunha,Luís Pereira

doi:10.3390/rs70302373

Isabel Pôças, Paula Paredes + Show 3 more

Open Access

https://doi.org/10.3390/rs70302373

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Journal: Remote sensing	Publication Date: Feb 27, 2015
Citations: 63	License type: CC BY 4.0

Affiliation: University of Lisbon, University of Porto

Abstract

A new procedure is proposed for estimating actual basal crop coefficients from vegetation indices (Kcb VI) considering a density coefficient (Kd) and a crop coefficient for bare soil. Kd is computed using the fraction of ground cover by vegetation (fc VI), which is also estimated from vegetation indices derived from remote sensing. A combined approach for estimating actual crop coefficients from vegetation indices (Kc VI) is also proposed by integrating the Kcb VI with the soil evaporation coefficient (Ke) derived from the soil water balance model SIMDualKc. Results for maize, barley and an olive orchard have shown that the approaches for estimating both fc VI and Kcb VI compared well with results obtained using the SIMDualKc model after calibration with ground observation data. For the crops studied, the correlation coefficients relative to comparing the actual Kcb VI and Kc VI with actual Kcb and Kc obtained with SIMDualKc were larger than 0.73 and 0.71, respectively. The corresponding regression coefficients were close to 1.0. The methodology herein presented and discussed allowed for obtaining information for the whole crop season, including periods when vegetation cover is incomplete, as the initial and development stages. Results show that the proposed methods are adequate for supporting irrigation management.

Highlights

The accurate estimation of crop water requirements plays an important role in the improvement of crops water use and irrigation performance
Considering the advances and limitations discussed above, the need to represent actual rather than potential crop and evapotranspiration conditions for irrigation management purposes, the main objectives of this study are: (i) developing and testing a new equation for estimating actual Kcb based on vegetation indices (VI) and considering the stress coefficient Ks and the density coefficient Kd computed with the fraction of ground cover fc estimated with VI; (ii) developing and testing a combined approach for estimation of the actual Kc using the VI-based Kcb and the evaporation coefficient Ke obtained with a daily soil water balance model; and (iii) testing the adequacy of the approach to different crop types, namely maize, barley, and an olive orchard
The results obtained indicate a better performance of Soil Adjusted Vegetation Index (SAVI) for the computation of the fraction of ground cover for the incomplete cover crop, olive, and of the Normalized Difference Vegetation Index (NDVI) for the annual crops, maize and barley

Summary

Introduction

The accurate estimation of crop water requirements plays an important role in the improvement of crops water use and irrigation performance. This issue is relevant considering the need for intensification of irrigated agriculture and increased water scarcity in several regions of the world. Crop evapotranspiration may be computed directly from ground observations using a combination equation such as the Penman-Monteith equation [2,3]. This approach is more demanding than the Kc-ETo approach and is not used for operational purposes but limited to research.

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