UAVs challenge to assess water stress for sustainable agriculture

Agricultural Water Management 153(2015)9–19

Contents lists available at ScienceDirect

Agricultural Water

Management

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /a g w a

t

Review

UAVs challenge to assess water stress for sustainable agriculture

J.Gago a ,∗,C.Douthe b ,R.E.Coopman c ,P.P.Gallego a ,M.Ribas-Carbo b ,J.Flexas b ,J.Escalona b ,H.Medrano b

a

Applied Plant &Soil Biology,Department of Plant Biology and Soil Science,Faculty of Biology,Vigo University,Campus Universitario das Lagoas-Marcosende,36310Vigo,Galicia,Spain b

Research Group on Plant Biology under Mediterranean Conditions,Departament de Biologia,Universitat de les Illes Balears,Carretera de Valldemossa Km 7.5,07122Palma de Mallorca,Illes Balears,Spain c

Laboratorio de Ecofisiología para la Conservación de Bosques,Instituto de Conservación,Biodiversidad y Territorio,Universidad Austral de Chile,Casilla 567,Valdivia,Chile

a r t i c l e

i n f o

Article history:

Received 26May 2014Accepted 21January 2015

Available online 19February 2015

Keywords:UAVs

Remote sensing Water stress

Precision agriculture Multicopters Thermography

a b s t r a c t

Unmanned aerial vehicles (UAVs)present an exciting opportunity to monitor crop fields with high spatial and temporal resolution remote sensing capable of improving water stress management in agriculture.In this study,we reviewed the application of different types of UAVs using different remote sensors and compared their performance with ground-truth plant data.Several reflectance indices,such as NDVI,TCARI/OSAVI and PRInorm obtained from UAVs have shown positive correlations related to water stress indicators such as water potential («)and stomatal conductance (g s ).Nevertheless,they have performed differently in diverse crops;thus,their uses and applications are also discussed in this study.Thermal imagery is also a common remote sensing technology used to assess water stress in plants,via thermal indices (calculated using artificial surfaces as references),estimates of the difference between canopy and air temperature,and even canopy conductance estimates derived from leaf energy balance models.These indices have shown a great potential to determine field stress heterogeneity using unmanned aerial platforms.It has also been proposed that chlorophyll fluorescence could be an even better indicator of plant photosynthesis and water use efficiency under water stress.Therefore,developing systems and methodologies to easily retrieve fluorescence from UAVs should be a priority for the near future.After a decade of work with UAVs,recently emerging technologies have developed more user-friendly aerial platforms,such as the multi-copters,which offer industry,science,and society new opportunities.Their use as high-throughput phenotyping platforms for real field conditions and also for water stress man-agement increasing temporal and resolution scales could improve our capacity to determine important crop traits such as yield or stress tolerance for breeding purposes.

©2015Elsevier B.V.All rights reserved.

Contents 1.Introduction ..........................................................................................................................................102.UAVs applied to precision agriculture................................................................................................................103.

Remote sensing of plant physiology from UAVs .....................................................................................................133.1.Indices based on leaf/canopy reflectance .....................................................................................................143.2.Indices based on leaf/canopy temperature ...................................................................................................163.3.The challenge of measuring leaf chlorophyll fluorescence with UAVs .......................................................................164.UAVs aerial imagery ..................................................................................................................................185.

Future perspectives and concluding remarks ........................................................................................................18Acknowledgements ..................................................................................................................................18References ............................................................................................................................................

18

∗Corresponding author.Tel.:+34986812595.E-mail address:xurxogago@ (J.Gago).

/10.1016/j.agwat.2015.01.020

0378-3774/©2015Elsevier B.V.All rights reserved.