Exploring the use of Unmanned Aerial Vehicles (UAVs) with the simplified ‘triangle’ technique for soil water content and evaporative fraction retrievals in a Mediterranean setting

ABSTRACT

Information acquired from Unmanned Aerial Vehicles (UAVs) is frequently used nowadays in a variety of disciplines and research fields. The present study explores for the first time the combined use of UAVs with a newly proposed technique for estimating evaporative fraction (EF) and surface soil moisture (SSM). The investigation is performed in a typical Mediterranean setting, a citrus field with flat topography divided in two plots with different irrigation schemes, in Sicily, Italy, at which ground data acquired during an extensive field campaign in July 2019. Reasonable estimates of both EF and surface wetness were produced, with patterns in agreement to vegetation cover fragmentation, topography, and other site-specific characteristics. Validation shows average error of 0.053 for EF and of 0.040 cm³ cm⁻³ for SSM. The results are comparable or better to those reported in analogous studies performed in similar areas. This implies that the investigated approach performs well under the semi-arid conditions characterizing the experimental set up. To our knowledge, this study represents the first evaluation of the combined use of the ‘simplified triangle’ with very high-resolution UAV imagery. As such, the findings are of significance regarding the potential future use of the ‘simplified triangle’ approach particularly with very fine resolution imagery such as that provided by UAV for mapping and monitoring EF and SSM in agricultural and natural ecosystems.

Acknowledgements

Participation of Dr. Petropoulos has been funded by the ENViSIoN-EO Marie Skłodowska-Curie grant (grant No 752094), part of the European Union’s Horizon 2020 research and innovation programme. Part of the present collaborative work was also materialised in the framework of a short Term Scientific Mission (STSM) of the HARMONIOUS Cost Action which financially supported Dr Petropoulos’ visit between 4 to 15 February 2020 to the Department of Engineering of the University of Palermo, Italy. Authors thank also Dr. Mauro Lo Brutto for his help in collecting the GNSS data.

Author contributions

AM, GP, GC, and SM conceived and planned the experiments. AM and FC contributed to the experimental design of the spectroradiometric acquisitions and radiometric calibration of the images. GC, GP and SM coordinated the experiment and provided instrumentations. AM and GD contributed to the GNSS experimental design and processing. GP contributed to the experimental design and management of the soil moisture probes and processed the data. AM processed the flux tower data. SM and FC designed and acquired the UAV images. GPP, AP, TNC, DH and CC contributed to model implementation, results processing and analysis. GPP, AP prepared the original draft of the manuscript. All authors reviewed and edited the final version of the manuscript and contributed to the preparation of the revised manuscript.

Authors’ Initials are defined as follows

George P. Petropoulos (GPP), Antonino Maltese (AM), Toby N. Carlson (TNC), Giuseppe Provenzano (GP), Andrew Pavlides (AP), Giuseppe Ciraolo (GC), Dionissios Hristopulos (DH), Fulvio Capodici (FC), Christos Chalkias (CC), Gino Dardanelli (GD), Salvatore Manfreda (SM).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the FP7 People: Marie-Curie Actions [752094].