Abstract
Land surface temperature (LST) plays an essential role in developing and applying precision agriculture protocols, especially for calculating crop evapotranspiration (ETc) by surface energy balance (SEB) approaches; and for determining crop water status. However, LST is quite dependent on the meteorological conditions, which can rapidly vary. This variability, together with the limited meterological data acquisition frequency in most weather stations, can lead to the miscalculation of the SEB components, especially relevant when used for irrigation purposes.The present study assessed the temporal dynamic of LST in a very short period of time (20-minutes) through the acquisition of multiple thermal imagery. Additionally, a combination of SEB approach with Eddy Covariance technique was performed for quantifying the effect that LST variations have on the sensible (H) and latent (LE) heat fluxes.Even under steady meteorological conditions, temporal variations in LST of 3.5 and 4.0 K were observed for tree canopy and sunny bare soil surfaces, respectively. These LST oscillations reached values of about 7.8 and 17.9 K for tree canopies and bare soil when heterogeneous meteorological conditions were observed (i.e. cloud presence). Such LST differences translated into H and LE differences of about 26 and 19%, respectively; with variations up to 5 (for H) and 2.7 times (for LE) under fast-varying meteorological conditions.The obtained results suggest the necessity of acquiring thermal imagery when steady meteorological conditions exist or, otherwise, ensuring the collection of instantaneous meteorological data for applying post-processing corrections. This is of importance when incorporating the obtained ETc maps into precision irrigation protocols.
Highlights
An accurate determination of crop evapotranspiration (ETc) is essential for increasing the productivity of irrigated agriculture (Filgueiras et al, 2019; Gong et al, 2019)
DOYs 162–164 exhibited a smooth continuous shape of the Rn,eddy covariance (EC) rates, whereas in DOYs 161 and 167 a less steady time-response was observed with the presence of Rn,EC decline peaks
It was specially relevant for DOY 162, when a Rn,EC decrease of 52% was observed in one hour
Summary
An accurate determination of crop evapotranspiration (ETc) is essential for increasing the productivity of irrigated agriculture (Filgueiras et al, 2019; Gong et al, 2019). The estimation methods are mainly based on models (including energy balance, mass transfer, and the use of crop coefficients, Kc) characterized by different levels of complexity in terms of number of parameters implied for the ETc schematization. Some of these models have been combined with remote sensing (RS) information in order to obtain spatially distributed ETc estimates over wide areas (Paço et al, 2014; Ramírez-Cuesta et al, 2020; Consoli & Vanella 2014a, b)
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