The effect of pixel heterogeneity for remote sensing based retrievals of evapotranspiration in a semi-arid tree-grass ecosystem

Many satellite missions rely on modeling approaches to acquire global or regional evapotranspiration (ET) products. However, a current challenge in ET modeling lies in dealing with sub-pixel heterogeneity, as models often assume homogeneous conditions at the pixel level. This is particularly an issu...

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Bibliographic Details
Published in:Remote sensing of environment 2021-07, Vol.260, p.112440, Article 112440
Main Authors: Burchard-Levine, Vicente, Nieto, Héctor, Riaño, David, Migliavacca, Mirco, El-Madany, Tarek S., Guzinski, Radoslaw, Carrara, Arnaud, Martín, M. Pilar
Format: Article
Language:English
Subjects:
Aerodynamics
Airborne imagery
Aridity
Energy balance
Environment models
Evapotranspiration
Fluxes
Grasses
Heterogeneity
Hyperspectral imaging
Image resolution
Land cover
Land surface temperature
Land use
Latent heat flux
Pixels
Remote sensing
Satellites
Sensible heat flux
Sentinels for evapotranspiration
Spatial discrimination
Spatial resolution
Surface energy balance
Surface roughness
Tree-grass ecosystems
Turbulent fluxes
Uncertainty
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Summary:Many satellite missions rely on modeling approaches to acquire global or regional evapotranspiration (ET) products. However, a current challenge in ET modeling lies in dealing with sub-pixel heterogeneity, as models often assume homogeneous conditions at the pixel level. This is particularly an issue for heterogeneous landscapes, such as tree-grass ecosystems (TGE). In these areas, while appearing homogeneous at larger spatial scales pertaining to a single land cover type, the separation of the spectral signals of the main landscape features (e.g. trees and grasses) may not be achieved at the conventional satellite sensor resolution (e.g. 10–1000 m). This leads to important heterogeneity within the pixel grid that may not be accounted for in traditional modeling frameworks. This study examined the effect of pixel heterogeneity on ET simulations over a complex TGE in central Spain. High resolution hyperspectral imagery from five airborne campaigns forced the two-source energy balance (TSEB) model at 1.5–1000 m spatial resolutions. Along with this, the sharpened (20 m) and original (1000 m) Sentinels for Evapotranspiration (Sen-ET) products were evaluated over the study site for 2017. Results indicated that TSEB accurately simulated ET (RMSD: ~60 W/m2) when the pixel scale was able to robustly discriminate between grass and tree pixels (
ISSN:0034-4257
1879-0704
DOI:10.1016/j.rse.2021.112440