Articles | Volume 21, issue 7
Hydrol. Earth Syst. Sci., 21, 3879–3914, 2017

Special issue: Observations and modeling of land surface water and energy...

Hydrol. Earth Syst. Sci., 21, 3879–3914, 2017

Review article 28 Jul 2017

Review article | 28 Jul 2017

The future of Earth observation in hydrology

Matthew F. McCabe1, Matthew Rodell2, Douglas E. Alsdorf3, Diego G. Miralles4, Remko Uijlenhoet5, Wolfgang Wagner6,7, Arko Lucieer8, Rasmus Houborg1, Niko E. C. Verhoest4, Trenton E. Franz9, Jiancheng Shi10, Huilin Gao11, and Eric F. Wood12 Matthew F. McCabe et al.
  • 1Water Desalination and Reuse Center, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
  • 2Hydrological Science Laboratory, Goddard Space Flight Center (GSFC), National Aeronautics and Space Administration (NASA), Greenbelt, Maryland, USA
  • 3Byrd Polar and Climate Research Center, The Ohio State University, Columbus, Ohio, USA
  • 4Laboratory of Hydrology and Water Management, Ghent University, Ghent, Belgium
  • 5Hydrology and Quantitative Water Management Group, Wageningen University, Wageningen, the Netherlands
  • 6Department of Geodesy and Geoinformation, Technische Universität Wien, Vienna, Austria
  • 7Center for Water Resource Systems, Technische Universität Wien, Vienna, Austria
  • 8School of Land and Food, University of Tasmania, Hobart, TAS 7001, Australia
  • 9School of Natural Resources, University of Nebraska-Lincoln, Lincoln, Nebraska 68583, USA
  • 10State Key Laboratory of Remote Sensing Science, Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences and Beijing Normal University, Beijing, China
  • 11Zachry Department of Civil Engineering, Texas A & M University, College Station, Texas 77843, USA
  • 12Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey, USA

Abstract. In just the past 5 years, the field of Earth observation has progressed beyond the offerings of conventional space-agency-based platforms to include a plethora of sensing opportunities afforded by CubeSats, unmanned aerial vehicles (UAVs), and smartphone technologies that are being embraced by both for-profit companies and individual researchers. Over the previous decades, space agency efforts have brought forth well-known and immensely useful satellites such as the Landsat series and the Gravity Research and Climate Experiment (GRACE) system, with costs typically of the order of 1 billion dollars per satellite and with concept-to-launch timelines of the order of 2 decades (for new missions). More recently, the proliferation of smartphones has helped to miniaturize sensors and energy requirements, facilitating advances in the use of CubeSats that can be launched by the dozens, while providing ultra-high (3–5 m) resolution sensing of the Earth on a daily basis. Start-up companies that did not exist a decade ago now operate more satellites in orbit than any space agency, and at costs that are a mere fraction of traditional satellite missions. With these advances come new space-borne measurements, such as real-time high-definition video for tracking air pollution, storm-cell development, flood propagation, precipitation monitoring, or even for constructing digital surfaces using structure-from-motion techniques. Closer to the surface, measurements from small unmanned drones and tethered balloons have mapped snow depths, floods, and estimated evaporation at sub-metre resolutions, pushing back on spatio-temporal constraints and delivering new process insights. At ground level, precipitation has been measured using signal attenuation between antennae mounted on cell phone towers, while the proliferation of mobile devices has enabled citizen scientists to catalogue photos of environmental conditions, estimate daily average temperatures from battery state, and sense other hydrologically important variables such as channel depths using commercially available wireless devices. Global internet access is being pursued via high-altitude balloons, solar planes, and hundreds of planned satellite launches, providing a means to exploit the internet of things as an entirely new measurement domain. Such global access will enable real-time collection of data from billions of smartphones or from remote research platforms. This future will produce petabytes of data that can only be accessed via cloud storage and will require new analytical approaches to interpret. The extent to which today's hydrologic models can usefully ingest such massive data volumes is unclear. Nor is it clear whether this deluge of data will be usefully exploited, either because the measurements are superfluous, inconsistent, not accurate enough, or simply because we lack the capacity to process and analyse them. What is apparent is that the tools and techniques afforded by this array of novel and game-changing sensing platforms present our community with a unique opportunity to develop new insights that advance fundamental aspects of the hydrological sciences. To accomplish this will require more than just an application of the technology: in some cases, it will demand a radical rethink on how we utilize and exploit these new observing systems.

Short summary
We examine the opportunities and challenges that technological advances in Earth observation will present to the hydrological community. From advanced space-based sensors to unmanned aerial vehicles and ground-based distributed networks, these emergent systems are set to revolutionize our understanding and interpretation of hydrological and related processes.