Evaporative Fluxes and Surface Soil Moisture Retrievals in a Mediterranean Setting from Sentinel-3 and the “Simplified Triangle”

George P Petropoulos,Dionissios Hristopulos,Toby Nahum Carlson,Ionut Sandric

doi:10.3390/rs12193192

Abstract

Earth Observation (EO) makes it possible to obtain information on key parameters characterizing interactions among Earth’s system components, such as evaporative fraction (EF) and surface soil moisture (SSM). Notably, techniques utilizing EO data of land surface temperature (Ts) and vegetation index (VI) have shown promise in this regard. The present study investigates, for the first time, the accuracy of one such technique, known as the “simplified triangle”, using Sentinel-3 EO data, acquired for 44 days in 2018 at three savannah FLUXNET sites in Spain. The technique was found to be able to predict both EF and SSM with reasonable accuracy when compared to collocated ground measurements. Comparisons performed for all days together showed relatively low Root Mean square Difference (RMSD) for both EF (0.191) and SSM (0.012 cm3 cm−3) and good correlation coefficients (R) of 0.721 and 0.577, respectively. Both EF and SSM were also largely in agreement with land cover and seasonal variability. The present study comprises the first detailed assessment of the “simplified triangle”, in this case, using Sentinel-3 data and in a Mediterranean setting. Findings, albeit preliminary, are of significant value regarding the use of the investigated technique as a tool of environmental management, and towards ongoing, worldwide efforts aiming at developing operationally relevant products based on the Ts/VI feature space and EO data based on new satellites such as Sentinel-3.

Highlights

Earth’s natural processes and the relationships between soil-vegetation and the atmosphere components of the Earth system are topics of great importance for numerous disciplines covering a range of practical applications and research [1,2,3,4]
This work aimed at evaluating the ability of the “simplified triangle” inversion technique to estimate Evaporative fraction and Surface Soil Moisture from European Space Agency (ESA)’s Sentinel-3 Earth Observation (EO) data in a typical savannah ecosystem in the Mediterranean region
The results obtained based on a series of statistical metrics suggested that the technique is, in most cases, able to predict the evaporative fraction (EF) and surface soil moisture (SSM) with satisfactory accuracy

Summary

Introduction

Earth’s natural processes and the relationships between soil-vegetation and the atmosphere components of the Earth system are topics of great importance for numerous disciplines covering a range of practical applications and research [1,2,3,4]. For example, suggest that the Mediterranean will be subject to severe climate change, including increased temperatures and reduced precipitation [6] In this context, the accurate monitoring of parameters such as evaporative fraction (i.e., the ratio of instantaneous latent heat flux (LE) to net radiation (Rn)) and surface soil moisture (SSM) is of high priority. The accurate monitoring of parameters such as evaporative fraction (i.e., the ratio of instantaneous latent heat flux (LE) to net radiation (Rn)) and surface soil moisture (SSM) is of high priority Both are essential environmental parameters which play instrumental roles in numerous physical processes, and thereby affect the climate directly or indirectly [7,8,9]. Being able to accurately estimate their changes in both the time and spatial domains is undoubtedly of prime interest for many applications in numerous disciplines [10,11]

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