Toward a High-Resolution Monitoring of Continental Surface Water Extent and Dynamics, at Global Scale: from GIEMS (Global Inundation Extent from Multi-Satellites) to SWOT (Surface Water Ocean Topography)
Toward a High-Resolution Monitoring of Continental Surface Water Extent and Dynamics, at Global Scale: from GIEMS (Global Inundation Extent from Multi- Satellites) to SWOT (Surface Water Ocean Topography)
Catherine Prigent 0 1 2 3
Dennis P. Lettenmaier 0 1 2 3
Filipe Aires 0 1 2 3
Fabrice Papa 0 1 2 3
0 Laboratoire d'Etude en Ge ́ophysique et Oce ́anographie Spatiales, IRD , 18, avenue Edouard Belin, 31401 Toulouse , France
1 Estellus , 93, Boulevard de Se ́bastopol, 75002 Paris , France
2 Department of Geography, University of California , 1255 Bunche Hall, Box 951524, Los Angeles, CA 90095 , USA
3 Indo-French Cell for Water Sciences, IRD-IISc Joint International Laboratory, Indian Institute of Science , C V Raman Ave, Bangaluru, Karnataka 560012 , India
Up to now, high-resolution mapping of surface water extent from satellites has only been available for a few regions, over limited time periods. The extension of the temporal and spatial coverage was difficult, due to the limitation of the remote sensing technique [e.g., the interaction of the radiation with vegetation or cloud for visible observations or the temporal sampling with the synthetic aperture radar (SAR)]. The advantages and the limitations of the various satellite techniques are reviewed. The need to have a global and consistent estimate of the water surfaces over long time periods triggered the development of a multi-satellite methodology to obtain consistent surface water all over the globe, regardless of the environments. The Global Inundation Extent from Multisatellites (GIEMS) combines the complementary strengths of satellite observations from the visible to the microwave, to produce a low-resolution monthly dataset (0:25 0:25 ) of surface water extent and dynamics. Downscaling algorithms are now developed and applied to GIEMS, using high-spatial-resolution information from visible, near-infrared, and synthetic aperture radar (SAR) satellite images, or from digital elevation models. Preliminary products are available down to 500-m spatial resolution. This work bridges the gaps and prepares for the future NASA/CNES Surface Water Ocean Topography (SWOT) mission to be launched in 2020. SWOT will delineate surface water extent estimates and their water storage with an unprecedented spatial resolution and accuracy, thanks to a SAR CNRS, Laboratoire d'Etude du Rayonnement et de la Matie`re en Astrophysique et Atmosphe`res (LERMA), Observatoire de Paris, 61, avenue de l'Observatoire, 75014 Paris, France
-
in an interferometry mode. When available, the SWOT data will be adopted to downscale
GIEMS, to produce a long time series of water surfaces at global scale, consistent with the
SWOT observations.
Satellite remote sensing
1 Introduction
Terrestrial surface waters amount to less than 1 % of the total Earth water and cover less
than 6 % of the ice-free continents at any time (Shiklomanov 1993). However, they are the
source of most ( 2/3) of water consumed by humans (UN-Water 2007) and have a large
impact on the biodiversity and on the biogeochemical and hydrological cycles, along with
a key role on the climate variability. Continental surface waters encompass a very large
variety of environments and circumstances, from exceptionally flooded populated areas
and their related human loss, to strategic rice paddies to feed the populations, tropical
wetlands very rich in biodiversity, or climate-sensitive boreal peat land with their large
methane emission. The definition of wetlands varies according to research foci, and no
overall consensus on the subject exists.
Despite their importance, there is a lack of reliable, continuous, and consistent
information on the inundation extent and dynamics, at both global and regional scales, to satisfy
a large and diverse community of users. Mapping of surface waters involves a wide range of
users, practitioners, and stakeholders. These include water and disaster managers, insurance
companies, hydrologists, ecologists, weather forecasters, or climate modelers. Some
applications require high spatial resolution and temporal sampling with almost real-time
observations, and others will favor global low spatial resolution with long-term objectives.
The potential role of satellite Earth observations for the mapping of surface waters has
been stressed on many occasions, for different applications (e.g., Committee on Earth
Observation Satellites 2013; Global Earth Observations 2013; Convention on Biological
Diversity 2014). There are ongoing efforts to promote the satellite Earth observations for
surface water mapping in these fields (e.g., the Global Monitoring of Environment and
Security project DISASTER or the European Space Agency project GlobWetland I–III),
but all user needs are still far from being satisfied.
Current satellite remote sensing techniques can produce seamless global land cover
maps and distinguish many terrestrial environments, but still struggle to generate accurate
high-spatial-resolutio (...truncated)