Field scale partitioning of Landsat land surface temperature into soil and canopy components for evapotranspiration assessment using a two-source energy balance model

Authors: CAMMALIERI, C - University Of Milan; Anderson, Martha; BAMBACH, N - Department Of Land, Air, And Water; McElrone, Andrew; Knipper, Kyle; Roby, Matthew; Kustas, William

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2024
Publication Date: 10/19/2024
Citation: Cammalieri, C., Anderson, M.C., Bambach, N., Mcelrone, A.J., Knipper, K.R., Roby, M.C., Kustas, W.P. 2024. Field scale partitioning of Landsat land surface temperature into soil and canopy components for evapotranspiration assessment using a two-source energy balance model. Irrigation Science. https://doi.org/10.1007/s00271-024-00976-w.
DOI: https://doi.org/10.1007/s00271-024-00976-w

Interpretive Summary: The temperature of the land surface, which can be measured from satellites equipped with thermal infrared imaging sensors, provides valuable information about the moisture status of the crops and soil, and the rate at which the crops are consuming available water in the soil profile. Healthy crops and wet soils tend to be cooler, due to evaporative cooling, than are stressed crops and dry soils. This paper describes a simple method for estimating characteristic temperatures of the soil and vegetation from a set of satellite temperature measurements collected across the field, which will typically be coarse enough in resolution to reflect a mixture of both components. This ability to partition satellite temperatures into soil and vegetation temperatures provides a means to more accurately and robustly estimate water used beneficially by the crops (through transpiration) and water lost non-beneficially through soil evaporation beneath the crops and in the interrow. The method is demonstrated over several California vineyards and almond and olive orchards, and the utility for irrigation management in these types of structured woody perennial systems is discussed.

Technical Abstract: Application of the two-source energy balance (TSEB) model on satellite data requires the definition of canopy (Tc) and soil (Ts) temperatures for the partitioning of the latent heat flux into transpiration (T) and evaporation (E) components. In this study, we evaluate the possibility of directly separating the satellite land-surface temperature (LST) into soil and canopy components, removing the need to adopt the iterative solution currently used in the TSEB approach. The method exploits contextual information at field scale, under the assumption that the field is homogeneous and characterized by spatially uniform Tc and Ts values. The approach was tested on a set of fields with typical Mediterranean crops in California, and it was compared against the outcomes of two other standard versions of TSEB, as well as in-situ flux measurements. Overall, the proposed partitioning approach performs similarly to the standard TSEB models (mean absolute difference, MAD, in the order of 60 W m-2 for turbulent fluxes), with only a slight tendency to overestimate transpiration. Differences in transpiration are mostly driven by divergences in modelled Tc (MAD between 2 and 3 °C), whereas differences in Ts are more limited (MAD between 1 and 2 °C). The main discrepancies were observed over low canopy coverage conditions (fractional cover lower than 35%), where small changes in Ts resulted in large differences in Tc. Despite this drawback, the results show that the method is a suitable alternative for a more straightforward operational field-scale application of the TSEB.